Inpainting: Inpainting Binders and Media

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Compiler: Catherine A. Metzger

Hand-Mixed

Aqueous Binding Media

Egg Tempera

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Principal Name

Egg Tempera

The term tempera is derived from the Italian verb temperare, which translates into English as “to moderate, control, or temper.” The English verb “to temper” is defined as “to dilute or soften by the addition of something else (to temper justice with mercy).”

The word connotes that the pigments are tempered by the medium. This could, of course, refer to any paint, but is primarily used to mean a water-born, natural medium, usually egg.

Other Names

Dawson Carr and Mark Leonard define tempera as a water-based paint that can include both egg tempera and glue tempera; they note that glue tempera is sometimes called distemper or Tüchlein . Rutherford J. Gettens and George L. Stout also include casein and gum as kinds of tempera

Herbert Lank sometimes uses the term egg tempera emulsion paint as well as egg tempera paint and tempera paint.

History of Use

1. Industrial (Artistic)
Eggs have been used as artists’ materials since ancient times. Pliny describes the use of egg as a paint medium .

Eggs have two major components: the white (also called albumen) and the yellow or yolk; they can be used both separately and together. For easel paintings, they have most commonly been used separately, the yolk as a paint medium and the white as a varnish.

The preparation of glair from egg white is described in the De Clarea manuscript, a 12th-century copy of a text from the first half of the 11th century . Cennino Cennini writes of the use of egg white for gilding and for painting on parchment . Egg white has also been used as a varnish .

Cennini also mentions whole egg tempera, combining the yolk and the white. These are suggested for painting on walls and can either be made of a whole beaten egg or with the addition of natural latex from the fig tree. To do this, he describes adding clippings from fig shoots to the whole egg and beating the mixture. The laticifer tissue of the common fig, or Ficus carica, secretes latex, a thick, white complex emulsion of resins (terpenoids and phenolic compounds), proteins, acids, carbohydrates, tannins, alkaloids, and minerals (Langenheim 2003, 49). Presumably this would assist the adhesion of the tempera to the wall; Cennini notes that this is particularly useful for preparing plastered walls for oil paint.

Cennini described the technique of painting in egg tempera, writing in the early 15th century but describing traditions established at least 100 years before. His paint medium for use on a wooden panel prepared with a gesso ground uses only the egg yolk.

Although more Italian than Northern egg tempera paintings survive, egg was used throughout Europe. Surviving English examples include the late 14thcentury Wilton Diptych

As the use of drying oils as a paint medium increased in the early 15th century, egg tempera began to be less common. It was rarely used by European artists after the mid-16th century.

In the 20th century, there was renewed interest in egg tempera, which was used by such artists as Andrew Wyeth. Mark Rothko added egg to his oil paints for the Rothko Chapel .

2. Conservation
i. History
According to Mary Kempski, “In the 19th century, there was an upsurge of interest in the techniques of the ‘old masters’ and particularly in all forms of tempera painting, which ultimately encouraged the Nazarene and Pre-Raphaelite movements. It appears that tempera was first introduced in Germany as a retouching medium at this time. Christian Kӧster, painter and restorer with the Boisserée Collection and the Royal Berlin Museum, published a treatise entitled ‘On the Restoration of Old Oil Paintings’ in 1827. In this he described retouching on a white ground or on tempera underlayers with lean oil colours. The tempera was made from egg yolk and mixed with a little vinegar as a preservative. This technique was continued by Jakob Schlesinger, who worked with Kӧster at the Royal Berlin Museum. This method of retouching, however, was not without its critics. Jakob Roux, a painter and university professor in Heidelberg, wrote that egg yolk on its own, as a medium, would not have enough adhesion and suggested the addition of wax. These were the rather experimental beginnings of egg tempera retouching” .

The main tradition of egg tempera retouching thus derives from Germany. However, egg tempera retouching has also been used by conservators trained in non-Germanic traditions. It was often used by Mario Modestini and his studio in the 1950s on paintings in the Samuel H. Kress Collection. Egg tempera and egg tempera with dammar were evaluated (along with dammar alone and PVAc-AYAB) for use as inpainting media by Modestini and Gustav Berger in 1959–60 . Many practitioners in Europe, and to a lesser extent in the United States, continue to use egg tempera today.

As of this writing, egg tempera retouching is primarily associated with the Hamilton Kerr Institute, the conservation training program in the United Kingdom, and with restorations in continental Europe. Students are taught the method that is used on most paintings treated at the Institute .

The institute’s first director, Herbert Lank, has described his method of using egg tempera for retouching, which he learned from Helmut Ruhemann, with whom he apprenticed beginning in 1946 . Ruhemann was the head of paintings conservation at the National Gallery in London from 1934 to 1972.

According to Kempski, “Ruhemann brought the tempera retouching technique from Germany to England at the beginning of the [20th] century. [He] had spent four years at the Kaiser Friedrich Museum, Berlin…Ruhemann gained most of this conservation knowledge from his colleague, William Suhr, who also worked in Berlin and who ultimately became chief restorer at the Detroit Museum of Art. It is most likely that Ruhemann learnt the technique of tempera retouching from him”. Ruhemann was originally trained as an artist at the Academies of Art at Karlsruhe and Munich as well as with Max Liebermann, and in Paris with Maurice Denis . Sebastian Isepp, a contemporary of Ruhemann’s and chief restorer at the Kunsthistorisches Museum in Vienna, also used egg tempera for retouching

ii. Advantages
Egg tempera retouching exploits the characteristics of the medium to create quite convincing reconstructions of losses. Knut Nicolaus sees several advantages to the technique. “Egg tempera retouchings are among those that alter the least. Using egg tempera, one can closely emulate both the coloration and the characteristic structures of an old paint layer. In my opinion, egg tempera retouching is superior to the other techniques available today for retouching Old Masters. It yellows only slightly, is easy to structure, and in overall appearance looks like an old painting” .

Before the development of synthetic resins, restorers’ other options for inpainting media were resins (mastic and dammar), oils, waxes, and gums. Ruhemann was particularly disturbed by discolored retouching (as well as oxidized varnishes). “I found that the copious retouching on many Kaiser Friedrich Museum pictures had been done with ordinary oil paint and had turned into dark blotches, often encroaching on original paint. They were not obvious to the layman because they were concealed by the useful brown umber veil of tinted varnish” . Meanwhile, “watercolors bleached and broke up the varnish film, causing the retouched areas to ‘blanch’ and become white” . When zinc white was used with dammar, a reaction yielded zinc dammarate, also creating a blanched effect.

Egg tempera avoids these problems because, after the protein in the egg denatures, there is very little further chemical or physical alteration in the paint film and its appearance. The pigment is essentially locked within a stable matrix.

The insolubility of egg after denaturing means that it can be easily and cleanly layered and is thus ideal for recreating the layering structure of a painting. This can be more difficult with resins or watercolor; upper layers may re-dissolve underlayers.

The relatively low refractive index of egg (1.346) means that as a paint, it is relatively opaque. The retouching can consist of multiple thin layers and still not be thick and “blobby.”

Egg tempera is a water-based medium that does not expose the conservator to solvents that may cause health problems.

iii. Disadvantages
Preparation of egg tempera materials is more time-consuming than using manufactured media. It takes time to prepare the materials, carry out the retouching, and master the technique. As it is a self-made paint and thus involves working with unbound pigments, the potential for exposure to heavy metals may be greater.

The main drawback to the technique is also one of its greatest advantages: insolubility. If used over areas of original paint, the technique violates a fundamental criterion of modern conservation—reversibility.

Source

1. Physical: Poultry

2. Origin and manufacture: Poultry

3. Manufacturers and vendors: Poultry farmers

Chemical and Physical Properties

1. Chemical classification
The yolk and the white of eggs have different, but related compositions. “Egg yolk is an emulsion consisting of droplets of fatty material suspended and emulsified in a matrix of egg proteins in water” . Egg white is a mixture of proteins in water, with almost no fatty material. The proteinaceous part of each consists of a number of different proteins belonging to the albumin class. (Albumin should not be confused with albumen, a term used to refer to egg white.) These proteins serve as the truly binding part of the medium.

2. Chemical formula/structure
Fresh egg yolk is approximately half water; the remaining half contains roughly twice as many fatty compounds as proteins . Specific proteins found in egg yolk include

• phosphovitin (MW c. 21,000), a composite protein;
• α- and β-lipovitellins, lipoproteins containing phospholipids;
• α-, β-, and γ-livetins .

Egg yolk contains several emulsifiers, including cholesterol and lecithin . “The lecithin is a fatty substance to which has been given the empirical formula [math]\ce{ C42H84NPO9 }[/math] but it differs from most fats in containing nitrogen and phosphorus and in being very hygroscopic” . Yolk also contains trace amounts of phosphorous, manganese, iron, iodine, copper, calcium, and zinc.

The yellow color of the yolk comes from plant pigments known as xanthophylls contained in components of the hens’ feed, such as yellow corn, alfalfa meal, and marigold petals. These plant pigments are considered to be relatively stable, even when cooked [5]. Cennini writes that the yolks of country eggs are redder than those of town eggs . Presumably this is caused by a different diet.

Egg white consists of four alternating layers of thick and thin albumen. Fresh egg white is nearly 90 percent water, the remaining 10 percent being mostly protein. Specific proteins found in egg white include

• ovalbumin (MW c. 45,000), a glycoprotein (i.e., a protein linked to a carbohydrate) (50 percent of the protein in egg white)
• conalbumin (MW c. 85,000), a glycoprotein (15 percent)
• lysozyme (MW c. 17,000), the only non-glycoprotein in egg white .

Egg white also contains niacin, riboflavin, chlorine, magnesium, potassium, sodium, and sulfur.

According to the American Egg Board, “Albumen is more opalescent than truly white. The cloudy appearance comes from carbon dioxide. As the egg ages, carbon dioxide escapes, so the albumen of older eggs is more transparent than that of fresher eggs.” [6]

3. Solubility
According to Mills and White, “The albumins are readily soluble in water and belong to a class known as globular proteins. These are held in a tight ball conformation by internal hydrogen-bonding between adjacent amino acid clusters in such a way that the more polar, hydrophilic groups line the outer surface of the ball and the hydrophobic groups are folded away within. However, these albumins quickly ‘denature’ under the effects of heat and certain reagents, by which it is meant that they become insoluble (as when an egg is boiled.) What happens is that the internal hydrogen bonds rupture and the molecular structure opens up and adopts an open chain-like structure, the overall hydrophilic properties being lost”. Thus, after denaturing, egg proteins are no longer soluble in water.

Preparation and Formulation (Preparing the Medium)

1. Typical application methods
Numerous variations on making and using egg tempera exist. For this entry, the following method described by Herbert Lank—the Lank recipe—will be presented as the basic version:

“The whole egg, except the shell and chalaza (the fibrous strings that hold the yolk sac in position within the shell), is used. The egg is broken into a clean beaker, taking care not to break the yolk. Any fertilized egg, showing a blood spot, is discarded. The chalaza is removed with fine tweezers. The yolk and white are tipped into a bottle, which is then stoppered and shaken vigorously to mix the yolk and egg white together. Unlike in egg tempera painting, the albumen content of the white plays an essential role in the use of egg tempera as a retouching medium.

The egg in the bottle is an emulsion with a high water content. It is now diluted further by the gradual addition of purified water. The water content of every egg is not identical. The addition of up to a maximum of 60 percent water may be required. An excess of water will destroy the emulsion, allowing the constituents to separate and making the medium unusable.

After the addition of the water, the stoppered bottle is again shaken. Foam should not be allowed to form on the surface, as this can hinder the grinding of pigments into the medium. The emulsion will separate out if an excess of water is added. It is therefore advisable to add only the amount of water required to attain a workable viscosity for the medium. .”

This whole egg recipe would have a higher protein-to-fat ratio than the egg yolk tempera described by Cennini. This would change the “feel” of the paint, making it less greasy and may alter the refractive index of the medium.

There are numerous variations on the steps of preparation and ingredients of the medium. This author was taught by Renate Woudhuysen-Keller to whip the white separately, in accordance with the way glair is prepared. According to Woudhuysen-Keller, “Rolf E. Straub describes the characteristics of egg white varnish thusly: “Egg white has a cordlike macromolecular structure, which has to be broken up by beating”. According to Kempski, “Whipping egg white causes denaturation even before dehydration” . The white is beaten to a stiff peak. Separately, as much water in equal volume to the yolk is added to the yolk and lightly blended with a fork. The yolk is then added to the white, and the mixture is allowed to stand in a tall narrow container. The usable medium will collect at the bottom.

Once the medium is prepared, dry pigments are combined with it to create the paint. Lank states that “any permanent pigment can be used for tempera retouching”. As he uses tempera for body paint, the opaque pigments predominate. Doerner warns that “pigments containing sulfur, such as cadmium, vermilion, and artificial ultramarine, when used with an egg emulsion, may decompose by combining with the nitrogen and sulphur compounds in the egg to form hydrogen sulfide”.

The pigments must be ground into the medium, not simply mixed with an inpainting brush. This can be done, in small amounts, on the inpainting palette with a muller. A glass rod, polished to a flat, angled surface on one end, works well for this. Lank notes that “the less dense, transparent pigments are harder to grind into the medium” .

The ratio of medium to pigment is very important. The high pigment ratio that can be achieved with egg tempera is one of the reasons it is effective at mimicking the look of old oil paint. However, too little medium gives a powdery paint, whereas too much can lead to flaking. Different pigments require different amounts of medium; for example, earth pigments usually require more than heavy metal pigments. In addition, as the water content in the egg medium will vary, the ratio must be determined empirically. One can start with roughly equal proportions of medium to pigment. A good test is to paint out a small stroke on the palette, allow it to dry, judge its gloss, and rub lightly with a finger to test its durability.

Once the paint is made, it cannot be allowed to dry on the palette, as it cannot be re-dissolved. Gradual additions of water should be ground in over time.

2. Additives
Knut Nicolaus describes a variation that adds beeswax to the medium to ensure reversibility:

1. To make up the paint, first break a chicken egg, and separate the yolk from the white.

2. Dissolve some bleached beeswax in white spirit, measuring it in the rough proportion of 1:3 to form a wax paste.

3. With a spatula, mix the egg yolk with a pea-sized quantity of the wax paste.

4. Put the egg yolk and wax mixture into a glass, then add the egg white, seal the container, and shake the glass thoroughly.

5. Dilute the mixture with the same quantity of distilled water and a drop of vinegar as a preserve. (1998, 279)

Nicolaus also suggests adding a surfactant such as ox-gall to help the paint adhere to the fill.

David Bull employs the yolk of the egg (separated from the white) with a few drops of toluene as a preservative.

Other modern recipes for egg tempera paint, which may at times have been used for inpainting, may be more or less complicated. To his yolk-only medium, Thompson recommends adding “two or three drops of vinegar or 3 percent acetic acid as a preservative and to make the medium less greasy”. Doerner advises against adding vinegar or phenol because they may cause discoloration of the pigments, but suggests adding a drop of oil of cloves or a small amount of alcohol .

3. Storage/shelf life
The egg medium should be refrigerated when not in use. Even with refrigeration, it will only remain fresh for a few days. One suggestion is not to cover the container too tightly, to prevent buildup of sulfur.

Handling Characteristics

1. Appearance
The aim of egg tempera retouching is to recreate the layering structure of the painting. This is considered to give the most convincing appearance and be convincing over a long period of time. “A clean and unobtrusive retouching is achieved, which, should the upper glazing layer become more transparent, will nevertheless be found acceptable.”

Because it is an emulsion, the paint will undergo several changes in tonality. Lank describes these steps:

1. Changes between the wet mix on the palette and the newly applied paint

2. A darkening of the paint when dry

3. A slight drop in tonality after burnishing

4. A marked enhancement of the colors and a drop in tonality when the paint is saturated with white spirit or varnished

“Once the tempera retouching has been lightly burnished and thinly varnished, it should generally be very slightly lighter and cooler in tonality than the original paint. This allows for a final glazing layer, which will turn the tempera retouching slightly darker and warmer, finally matching the surrounding original paint”

2. Application
As a rule, egg tempera use should be restricted to filled loss areas, as it will become insoluble. As the retouching will later be burnished, soft fills such as wax are not suitable. In general, because of its insolubility and because it is difficult to apply in pinpoint areas, egg tempera is not used on unfilled areas, such as abrasion. The fill should be sealed and the painting varnished; the varnish will also aid in future removal of the tempera inpainting.

In Lank’s procedure, first the fill is toned with a glaze of resin tinted with transparent pigments, such as raw sienna and black; the aim is to imitate a laying-in tone or an aged ground. “Care must be taken to keep the resinous medium to a minimum, as the tempera layer would not be easy to apply on top of a thick resinous surface. This layer should be allowed to dry. Subsequent solvent evaporation can otherwise cause fissures in the tempera paint”. At the Hamilton Kerr Institute, this resin is usually MS2A, which is also used as the varnish. Nicolaus suggests a natural resin varnish.

As described above, egg tempera is used in conjunction with a resin-based glazing medium. This is used as both the first and last layer, between which the egg tempera is sandwiched, and can be used alone on areas of abrasion.The difference in solubility between the resin and the egg is exploited to keep the layers crisp. It should be noted that the resinous medium is seen as being the “weak link” in the inpainting, the part that may lead to later color shifts that may make the inpainting more visible. Therefore, it is generally used sparingly.

The paint is applied by brush. It can be allowed to dry naturally (by evaporation and denaturing) or, as Lank suggests, be dried with a small hand-held hair dryer. Once dry, it is burnished lightly with an agate burnisher. (Nicolaus describes, instead, “polishing the surface lightly with a silk cloth”. It is then thinly varnished. Some practitioners burnish and varnish after each layer of paint is applied, others only after the final layer.

3. Modifications for special applications and effects (“Tricks of the Trade”)
Many practitioners apply egg tempera directly onto the fill, without a resin layer between. In this practice, the egg tempera can only be used for discrete paint losses, and not to replace missing glazes.

Aging Characteristics

1. Chemical process
“The first stage in the drying of egg tempera paint is therefore the evaporation of the water, followed by the denaturing of the egg proteins to a hard waterproof film…The egg fats are largely non-drying in character and, in part at least, survive little changed, perhaps serving to plasticize the paint”

2. Resultant chemical and/or physical alterations
The egg itself is more than 75 percent water; more water may have been added while making the medium, and dry pigment has been added. It is difficult to say what the final water content of the paint may be. Nevertheless, as it dries, the paint loses volume and tension is created in the layer, which may make it brittle and somewhat porous.

3. Impact on appearance, solubility, and removability
The whole-egg medium matrix surrounding the pigment particles is almost equal proportions of denatured protein and non-drying lipids. Thus, in theory, it would be more easily removable than pure egg white varnish. In addition, the inpainting has been sandwiched in between two layers of soluble varnish.

4. Attraction and retention of dirt and grime
Egg tempera retouching should be sealed with varnish to protect it from dirt and grime.

Jean Dommermuth

Submitted October 2006

Aquazol

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Principal Name

AquazolⓇ

Other Names

Poly(2-ethyl-2-oxazoline) (PEOX)

History of Use

1. Industrial
In 1977, the Dow Chemical Company was issued the first in a series of patents for a new polymer, poly(2-ethyl-2-oxazoline), or PEOX (Chamberlin 1977). This tertiary amide polymeric material was found to exhibit some unusual physical and chemical properties (such as solubility with relatively low viscosities in water, thermal and mechanical stability, etc.), suggesting a variety of possible industrial uses. The first comprehensive review of the physical and chemical properties of PEOX was published by Chiu and coworkers (Chiu, Thill, and Fairchok 1986). Among other properties, its refractive index was found to be the same as glass (1.520). PEOX is miscible with a number of common polymeric materials, often giving blends with single glass transition temperatures, and therefore is potentially useful for enhancing the adhesion of various polymer blends to a wider range of substrate materials. PEOX’s glass transition temperature of 55°C,¹ in combination with its water solubility, suggested possible uses, such as in biodegradable heat-seal packaging adhesives.

In the early 1990s, Dow licensed production of the polymer to Polymer Chemistry Innovations, which is producing it on a limited scale under the trade name Aquazol, in molecular weight ranges of 5,000 g/mol; 50,000 g/ mol; 200,000 g/mol; and 500,000 g/mol and labeled as Aquazol 5, 50, 200, and 500 respectively. Aquazol has found uses as a hot-melt adhesive and in some pressure-sensitive adhesives. It has gained acceptance as a greenware binder because of its clean burnout and nonionic nature. Aquazol has been approved by the FDA as an indirect food additive (adhesive).

2. Conservation
In the early 1990s, Richard Wolbers became interested in the potential of Aquazol for certain conservation applications, specifically noting that because Aquazol’s refractive index is virtually the same as glass, it might be useful as a consolidant for flaking reverse glass paintings. In 1994, a paper authored by Richard C. Wolbers, Mary McGinn, and Deborah Duerbeck, titled “Poly(2-ethyl-2-oxazoline): A New Conservation Consolidant,” was presented at the symposium “Painted Wood: History and Conservation” in Williamsburg, Virginia. The paper outlined the polymer’s physical and chemical properties, as well as the results of aging and other tests conducted by the authors. Case studies illustrating the use of Aquazol 50 and/or 500 as a paint-to-wood consolidant were presented, and its potential for other conservation uses—such as replacement gilding or as a binder for water-based inpainting—were suggested.

At the 1995 Paintings Specialty Group presentations (at the 23rd Annual Meeting of AIC in St. Paul, Minnesota), Mark Lewis presented a paper he coauthored with Richard Wolbers titled, “Evaluation of the Suitability of Poly(2-ethyl-2-oxazoline) as a Potential Retouching Medium for Easel Paintings.” The paper covered a continuation of the earlier testing of Aquazol by Wolbers, McGinn, and Duerbeck, focusing more specifically on its light aging characteristics when used as a pigment binder.

Soon thereafter, other formal presentations to the conservation profession began including various uses of Aquazol as an inpainting medium. For example, at the 1996 Annual Meeting of the Western Association for Art Conservation in Las Vegas, Nevada, Chris Stavroudis presented a paper that included his use of pigmented Aquazol 50 bulked with fumed silica for the reversible inpainting of a Jasper Johns encaustic painting.

Aquazol is currently used in conservation for a wide range of treatment procedures in addition to its use as an inpainting medium, including, but not limited to, consolidation of matte or friable paint, treatment of flaking or lifting paint layers, treatment of gilding, as an adhesive, as a component of fill materials, and as an isolating layer or barrier film (see Arslanoglu 2004).

Source

1. Physical
Solid, colorless to light yellow, translucent crystalline granules or pellets. The solid forms of the four molecular weight grades in current production: 5,000; 50,000; 200,000; and 500,000 g/mol; each has a slightly different appearance.

2. Origins and manufacture
The synthetic polymer is prepared by a cationic ring-opening polymerization of the monomer 2-ethyl-2-oxazoline (CAS Number2: 10431-98-8), with methyl tosylate as an initiator.

Figure 1 Polymerization of Aquazol, Courtesy of Mark van Gelder

According to the Materials Safety Data Sheet for Aquazol, the percentage of unpolymerized monomer remaining in the final product is <0.1%. However, according to quoted information from Richard Wolbers (McGinn 2009), he has found that methyl tosylate (or methyl-p-toluenesulfonate) from most suppliers (such as Shanghai Aladdin Chemical Company) comes as a 97% grade, which varies in color from white to pale yellow to brown, and that the discoloration of some Aquazol batches and solutions is due to the residual initiator rather than to any deterioration of the Aquazol polymer itself.

3. Manufacturers and vendors
Dow Chemical Company licensed production of Poly(2-ethyl-2-oxazoline) to Polymer Chemistry Innovations, Inc. in the early 1990s. Polymer Chemistry Innovations³ produces the polymer under the trade name Aquazol. Distributors supplying retail quantities of Aquazol to the conservation community are listed at the end of this chapter.

Chemical and Physical Properties

1. Chemical classification
Tertiary amide polymer resin CAS Number: 25805-17-8

2. Chemical formula/structure
Poly(2-ethyl-2-oxazoline), also known as PEOX.

Figure 2 Chemical structure for Aquazol, Courtesy of Mark van Gelder

3. Solubility
Aquazol is soluble in water, readily soluble in alcohols such as ethanol and methanol and in ketones such as acetone and methyl ethyl ketone, as well as in methylene chloride and propylene glycol. Aquazol is slightly soluble in toluene and n-pentane.

The manufacturer’s Technical Information Sheet states that Aquazol’s pH in aqueous solutions is neutral and that it is stable in weak acids and bases (but strong acids or bases will hydrolyze the amide group).

The manufacturer’s literature also indicates that, as might be expected, the lower molecular weight grades are more flexible and water soluble compared to the higher molecular weight products, which have more “strength.”

Aquazol solutions in solvent mixtures (for example, of water with acetone or with alcohols such as ethanol or isopropanol) have been used in various conservation treatments (see Arslanoglu 2004).

From the Manufacturer’s Technical Information:

n-Pentane	P
Toluene	P
Methyl ethyl ketone	S
Methylene chloride	S
Acetone	S
Propylene glycol	S
Ethanol	S
Methanol	S
Water	S

Source: P = solubility of 2% or less by weight"
Source: S = solubility of 25% or more by weight"

From Chiu, Thill, and Fairchok (1986):

Toluene	P
Ethanol	S
Acetone	S
Isopropanol	N
Arcosolv PM/1-Methoxy-2-Propanol	N
Shell Cyclo Sol 100 / Shell Cyclo Sol 53	N
Shell Odorless Mineral Spirits/Shell Sol 71	N
Stoddard solvent/Shell Sol 340 HT	N
Shell Mineral Spirits 145	N
Petroleum Benzine	N
Turpentine	N
Xylene	N

Source: P = solubility of 2% or less by weight"
Source: S = solubility of 25% or more by weight"
Source: N = not tested"

More extensive and precise solubility testing of Aquazol 50, 200, and 500 was done as a graduate student project at the Buffalo State College Art Conservation Program by Dawn Rogala (class of 2006), under the direction of Professor James Hamm. The solubility of Aquazol 200 was subsequently plotted in Teas Chart format at the BSC Art Conservation Program by students in the 2009 class, under the direction of Professor Gregory Dale Smith.

4. Tg (glass transition temperature)
In 1986, Chiu, Thill, and Fairchok reported a Tg value for PEOX of 55oC [~125oF]. Technical information for Aquazol provided by the present manufacturer states, “Glass Temperature: 69–71oC (amorphous)” [~154–159oF]. As noted above, at 50% RH and 74oF, Aquazol achieves an equilibrium moisture content of ~5–8% by weight. This moisture content acts as a plasticizer and apparently lowers the Tg closer to the 55oC figure. Like most polymers, the glass transition temperatures of the lower molecular weight (MW) Aquazols exhibit lower Tgs than the higher MWs. The lower MW Aquazols are also more water soluble and hydrophilic, which have a slightly greater effect on lowering their glass transition temperatures.

5. Molecular weights
The polymer is presently produced by Polymer Chemistry Innovations in four molecular weight ranges: Aquazol 5 (5,000); Aquazol 50 (50,000); Aquazol 200 (200,000); and Aquazol 500 (500,000). These are weight average molecular weights (g/mol), with a polydispersity range of 3–4. Polymer Chemistry Innovations has also custom-made some other molecular weights and forms of Aquazol (such as low molecular weight copolymers) for specific industrial purposes.

6. Refractive index
nD = 1.520 + 0.001 (Chiu, Thill, and Fairchok 1986; Polymer Chemistry Innovations’ Technical Information Sheet 2001). Note that this is similar to the refractive index for common glass of ~1.529.

7. Brittleness and flexibility
Aquazol’s water solubility makes its flexibility and other strength characteristics subject to ambient relative humidity conditions, but even at very low RH values it exhibits Young’s modulus⁴ characteristics for an extremely plastic material. Yield stresses and strains do decrease slightly at low percentage RH levels, but even at 8% RH, Aquazol 500 has an elongation to break (eB) of 380% (Wolbers, McGinn, and Duerbeck 1994). By comparison, hide glue has an elongation to break of only 2–3% at 8% RH. According to the manufacturer’s data, Aquazol in granular form at 50% RH and 74oF achieves and maintains an equilibrium moisture content of ~6% by weight (in about 10 days). According to Richard Wolbers, this moisture content will act as a plasticizer even after the rest of the original carrier solvent or solvents have evaporated (phone conversation, June 2002).

RH	% Elongation to Yield	Yield Stress (kg/m)	% Elongation to Break	Breaking Stress (kg/m)
8%	44.62	380	53.57
33%	25	40.17	450	43.10
73%	50	17.85	550	26.78

Tensile strength data for Aquazol 500 conditioned at various RHs" (Wolbers, McGinn, and Duerbeck 1994)"

8. Specific gravity/density
The product’s MSDS sheet gives a value of 1.14 (water=1).

Preparation and Formulation

1. Typical application methods
Paints can be prepared using the various molecular weight grades of Aquazol as a binder in a range of solvents or solvent combinations (including water), as well as with a very wide range of solution and pigment concentrations, creating an extensive spectrum of possible paint characteristics. Inpainting formulations using Aquazol can be tailored to visually imitate many types of painted surfaces, from matte to glossy and from thin glazes to thick pastes.

Julie Arslanoglu (2004) conducted an overview of responses to a survey about how conservators are using Aquazol. In the section on Aquazol as an inpainting medium, the following typical formulations are discussed: Most commonly, concentrated stock solutions of Aquazol 50 or 200 in water are diluted as necessary and then mixed with dry pigments, or added to watercolors or gouache tube colors. Aqueous stock solutions are usually made up quite thick initially (and later diluted as needed for use) for each of the molecular weights of Aquazol at approximately the following concentrations:

• ~67% wt./vol. for Aquazol 50
• ~33% wt./vol. for Aquazol 200
• ~18–20% wt./vol. for Aquazol 500

More concentrated aqueous solutions than those above, as well as blends of the different molecular weights, have also been used for inpainting particular types of surfaces, for example, a 40–50% solution of equal parts Aquazol 200 and Aquazol 500 (used for inpainting gouache and enamel paint on paper).

Aquazol has also been used as an inpainting medium in solutions of alcohol (usually ethanol or isopropanol), acetone, and in mixtures of water:alcohol and water:acetone, such as in the following examples:

• 10% Aquazol 200 in ethanol (faster drying than in water).
• 10% Aquazol 200 in 95% water and 5% ethanol (reduces surface tension).
• Aquazol 50 in 1:1 or in 80:20 water:ethanol (applied with a nebulizer to imitate very chalky gouache).

Diluting Aquazol with a mixture of 10–40% acetone in water (which Jim Bernstein refers to as “water extra dry”) reduces surface tension as well as modifying characteristics such as drying time and final surface sheen.

2. Additives
No specific additives are required to use Aquazol as an inpainting medium. However, Aquazol is compatible with a wide variety of possible additives to modify its working properties or other desired characteristics. Adding a small amount of a secondary solvent to a solution of Aquazol can improve its handling properties over those in just the primary solvent alone. For example:

• Adding some ethanol or acetone to a water-based solution will reduce surface tension and viscosity, thus improving wetting and flow. A very small amount of Kodak Photo-FloⓇ can also be added to aqueous solutions to improve wetting (reduce “beading up”) on some surfaces.

• Adding some aliphatic solvent, such as naphtha, to a primarily alcohol-based solution might be used to extend the working time, and reduce the overall polarity of the carrier solvent mixture, if necessary.

Aquazol is compatible with many polymers, including PVAc and wax. It can be bulked with fumed silica or clay for gap filling or as a substitute for traditional bole or gesso (see below under “Modifications for special applications and effects/Tricks of the Trade”).

3. Storage/shelf life
Given the general stability of Aquazol, the manufacturer considers the shelf life to be essentially infinite. The manufacturer’s Technical Information Sheet states that Aquazol has a “Degradation Onset of > 380°C (TGA in air),” indicating stability under normal conditions. However, the product must be kept tightly sealed because it will absorb ambient moisture and a variety of other volatile materials in the immediate environment. Aquazol in granular form kept at 50% RH and 74oF achieves an equilibrium moisture content of ~5% water by weight.

The survey and subsequent article by Julie Arslanoglu (2004) concerning the use of Aquazol in conservation practice includes some additional information related to Aquazol’s shelf life. Aquazol’s synthetic PEOX polymer does not support mold growth in either aqueous or other solvent solutions, and solutions have been stored for many years without evidence of mold growth, as long as the containers remain uncontaminated by other sources. Some conservators have observed cold flow (i.e., gradual “slumping” in the container) of the lower molecular weight grades (Aquazol 50 and sometimes Aquazol 200) in their studios over time under typical storage conditions.

As mentioned above, the polymerization initiator, methyl tosylate (or methyl-p-toluenesulfonate), presently used in the manufacture of Aquazol, is supplied as a 97% grade, which varies in color from white to pale yellow to brown. According to Richard Wolbers, any perceived discoloration of Aquazol batches and solutions is due to this residual catalyst rather than to any deterioration of the Aquazol polymer itself.

Handling Characteristics

1. Appearance
Aquazol is supplied as translucent, colorless to light yellow granules or pellets. Yellowish or brownish color variations have been observed in some batches of Aquazol resin (Arslanoglu 2004), but the manufacturer considers these to be within the specification limits for the product (which is not designed for use as a conservation material). The mixing of yellowish or brownish Aquazol solutions with light inpainting colors may have an undesired effect on their appearance.

The lower molecular weight grades of Aquazol (i.e., Aquazol 50) tend to wet pigments better than the higher molecular weight grades. Solutions or mixtures using the higher molecular weight Aquazol 500 have a tendency toward drying with a glossy sheen (which can be either an advantage or disadvantage, depending on the final results desired). Films of Aquazol 500 are flexible, but can form a skin that may be prone to peeling, scaling, or scratching.

The absorbency of the surface being inpainted to the solution of Aquazol being used needs to be taken into account, so that the support does not draw off too much of the carrier solvent(s) or binder. The Aquazol paint should be viscous enough so that the inpainting remains appropriately saturated.

2. Application
Since Aquazol-based inpainting formulations can be created in a wide array of pigment/binder ratios, viscosities, and dilutions, ranging from water-thin glazes to stiff opaque pastes, a similarly broad range of appropriate application techniques can potentially be employed, including brush, spray, palette knife, roller, nebulizer, syringe, etc.

Some typical formulations used by conservators are discussed above under Preparation and Formulation, “Typical Application Methods.”

Conservators responding to Julie Arslanoglu’s survey described the Aquazolbased paints they used as having characteristics like a fuller-bodied opaque gouache, with sheen, or as having an “oil paint consistency.” In practical terms, a 10% solution in deionized water of any of the available molecular weights produces a working solution of dissolved Aquazol resin having more or less familiar viscosities, binding characteristics, and film forming properties.

A 10–15% solution of Aquazol 50 or Aquazol 200 in water can be sprayed or airbrushed, because even relatively concentrated aqueous solutions of the higher molecular weight grades of Aquazol generally have much lower viscosities at similar concentrations than many other water-soluble polymers.

Drying time will vary depending on ambient humidity and temperature levels, but can be modified by the use of carrier solvents, or combinations of solvents, having different evaporation rates—for example, combining various amounts of ethanol or acetone with aqueous solutions.
3. Modifications for special applications and effects (“Tricks of the Trade”)

Julie Arslanoglu’s article contains a great deal of information and examples of how conservators have used Aquazol in a variety of specific applications (2004).

• Aquazol can be used for reversible inpainting of surfaces with high wax content (or other particular solvent sensitivities)—for example, Chris Stavroudis’ use of watercolor in Aquazol 50 bulked with fumed silica for inpainting of a Jasper Johns encaustic painting (1996); and Carolyn Tomkiewicz’s use of Aquazol 200 mixed with watercolors for inpainting losses in a contemporary oil painting having a high wax content in the original paint (1999) (20 grams of Aquazol 50 in 30 grams of water, bulked with fumed Silica makes a translucent solution with a wax-like appearance).

• Aquazol can be useful for safely inpainting acrylic paintings, since it does not fuse to, swell, or solubilize the original paint the way typical solvent-based inpainting resins might.

• Jim Bernstein has observed that the different molecular weight grades of Aquazol, when mixed with the same pigment, often exhibit characteristics of binding media having different effective refractive indices. It appears that the difference in molecular size of the different weight grades optically saturates the pigment in different ways or to different extents (the lower molecular weight grades saturating the pigments more than the higher molecular weight grades). The variations in final appearance can be quite dramatic, akin to differences in saturation that the pigment might exhibit in oil versus aqueous media. This characteristic of Aquazol can be exploited—with pigments such as raw umber or ultramarine, for example—to render similar pigment to binder ratios either pale and light or dark and saturated in appearance.

• The addition of 20% Aquazol 500 to a watercolor palette improves the glaze quality of the paint. The paint remains transparent and reversible, but it can be particularly useful for glazing abraded paint surfaces.

• Inpainting with Aquazol in water can be done over the top of or in between other solvent-based inpainting or varnish layers, with much less tendency to disrupt the underlying layer(s). For example, inpainting using Aquazol in water was layered with Regalrez in Shellsol to inpaint scratches in multiple layers of acrylic emulsion glazes.

• Aquazol films cast from solutions containing water will probably retain about 5% moisture content by weight within the dried polymer matrix, apparently even in a fairly low humidity environment. The retained water acts as a plasticizer and lowers somewhat the effective glass transition temperature of the dried Aquazol. The lower molecular weight grades of Aquazol may be slightly more hygroscopic and/or have their physical properties more affected by the retained moisture content. Wolbers makes use of this in applications where the strength of higher molecular weight is desired along with added plasticity. For example, he might add 10% water to a solution of Aquazol 500 in isopropyl alcohol for this reason (personal communication, June 2002).

• The surface to be inpainted can be pre-desiccated by blowing air on it. The inpainting dries more quickly, with a richer color that does not have the same tendency to blanch, as might be the case if one was just using a faster evaporating solvent.

• Aquazol 500 has been used as a substitute for hide glue in making gesso putty, and in bole for conservation gilding. The gesso putty made with Aquazol has a number of qualities that differ from traditional gesso; for example, it can be tooled with heat, but it is more plastic-like and is not really carvable. Furniture conservator Chris Shelton developed a method of using bole made with 10–20% Aquazol 500 in alcohol for gilding. It dries quickly and is burnishable. It is compatible with traditional water gilding in that it is hygroscopic, but delivered and reversible in solvents other than water.

Aging Characteristics

1. Chemical process
The 1994 paper by Wolbers, McGinn, and Duerbeck (1998) outlined the results of various accelerated aging tests the authors had conducted on poly(2- ethyl-2-oxazoline). Films of Aquazol cast from 20% solutions in deionized water were exposed to accelerated light aging in a Weatherometer for the equivalent of approximately 24 years of natural aging under normal museum conditions (i.e., exposure under light sources that produce irradiances in UV wavelengths of 75 mW/m2 or less). Properties of unaged and artificially light aged samples were compared using a variety of test methods, including Size Exclusion Chromatography (SEC) (to determine molecular weights); pH measurements (to determine initial pH and whether aging produced any ionizable functional groups on the polymers); Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA) (to determine heat stability); resolubilization rates of cast films in various solvents; viscosity measurements (to determine molecular weight /polymer size changes); Infrared Spectroscopy (FTIR) (to determine whether oxidation or delamination, etc., had resulted in any gross chemical changes after light aging); color measurements; and Tensile Strength Tests.

The light aging tests on cast films of Aquazol 50 and 500 showed virtually no changes in color, FTIR spectra, pH of solutions, or resolubility after aging. The polymer also appeared to be thermally very stable.

Drops in molecular weight after light aging of Aquazol were suggested by both lowered solution viscosities and by shifts in SEC elution times.

2. Resultant chemical and/or physical alterations
Controlled test results seem to indicate that decreases in molecular weight, rather than cross-linking or any gross chemical alterations, are the main result of artificial light aging in the Aquazol polymer.⁵ Although chain scission is preferable to cross-linking, especially in terms of reversibility in conservation applications, some eventual loss of particular mechanical properties related to polymer size might gradually occur in some situations.

3. Impact on appearance, solubility, and removability
No yellowing, discoloration, or other significant changes in appearance were indicated by accelerated light aging tests of cast films (equivalent to 24 years of standard museum lighting exposure) conducted by Wolbers, McGinn, and Duerbeck.⁶

Resolubility testing of Aquazol 50 and 500 after artificial light aging (also conducted by Wolbers, McGinn, and Duerbeck) revealed that aged films remained essentially resoluble in the same solvents they were soluble in initially.

Mark Lewis and Richard Wolbers evaluated the potential for changes in resolubility of the Aquazol polymer mixed with pigments after accelerated light aging (equivalent to ~30 years of museum light level exposure) using FTIR spectra and SEC determinations of molecular weight (Lewis 1995). When resolubilized in plain water, experimental results with some samples suggested that metallic ions associated with several of the tested pigments may form typical organometallic complexes with the polymer. Adding a small amount of the chelating agent EDTA to the resolubilizing water (to de-complex possible pigment-binder interactions) eliminated the initially observed apparent increases in molecular weight of the Aquazol binder/ pigment combinations after artificial aging. Based on these findings, adding ~1/2% EDTA, ammonium citrate, or a similar chelating agent to water being used to remove Aquazol-based inpainting may increase the ease of resolubility of the inpainting in water.

4. Attraction and retention of dirt and grime According to the manufacturer’s Technical Information Sheet, PEOX’s glass transition temperature is 69–71°C (~154–159°F). Since this second order Tg is well above any normal room temperature range, dried Aquazol films should not tend to attract or retain dirt and grime due to cold flow or thermal softening at room temperature. (By way of reference, Aquazol’s Tg of 69–71°C is in the same range as Dammar resin [67–75°C]).

The Tg for ParaloidⓇ B-72 is 40oC (104oF)]. Because Aquazol films are water soluble and hygroscopic, however, their softness and vulnerability to imbibing foreign particles will certainly increase under conditions of high ambient relative humidity. Aquazol in granular form kept at 50% RH and 74°F achieves an equilibrium moisture content of ~5% by weight in about 2 weeks. Even at very low RH values, Aquazol is an extremely plastic material.

5. Theoretical lifetime As noted above, testing by Wolbers, McGinn, and Duerbeck revealed that cast films of Aquazol 50 and 500 did not discolor and remained essentially resoluble in the same solvents they were soluble in initially after an accelerated aging exposure equivalent to 24 years of standard museum lighting. The polymer also appeared to be thermally very stable and showed virtually no changes in IR spectra or pH of solutions after that amount of accelerated aging. Aquazol’s sensitivity to relative humidity might shorten its effective useful lifetime in excessively damp, humid, or unstable RH environments.

Some conservators have voiced concerns about the potential for cold flow (“creep”) of the lower molecular weight grades of Aquazol (mostly Aquazol 50), based on observations of slumping of the raw material form in the container, as supplied. However, Richard Wolbers theorizes that when Aquazol is mixed with pigments for inpainting, a stiffer and more mechanically stable matrix may be formed that would reduce the potential for such “creep” in practice.

Health and Safety

1. Aquazol has been reviewed in accordance with section 311 and 312 of SARA Title III (the Superfund Amendments and Reauthorization Act)⁷ and found not to be in any hazard class.
2. No adverse health effects are known or expected for eye, skin, ingestion, or inhalation exposure, although use of standard protective procedures (appropriate gloves, goggles, dust respirator, etc.) is always advisable. Chronic exposure information is not available. Aquazol has been approved by the FDA as an indirect food additive. The MSDS toxicological information states, “Oral LD50 (rat): 3980 mg/Kg.”
3. Decomposition begins at 300°C, which may generate toxic fumes, including nitrogen oxides, carbon monoxide, and carbon dioxide. Autoignition temperature is >400°C.

Disposal

Dispose of in a manner consistent with federal, state, and local regulations. As of 4/15/2002, Aquazol is not regulated for transport under DOT, IMO, or IAAO regulations. Ecological information is not available.

Mark van Gelder

Submitted February 2010

Wax

Hand-Mixed Pigmented Wax

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The use of wax as a surface coating has been extensively researched by Carole Abercauph in Volume I of the Painting Conservation Catalog: Varnishes and Surface Coatings (1997, 201–209). A great deal of information specific to the use of hand-mixed wax is identical to that found in that publication and will not be repeated here. The reader is invited to refer to this volume for supplemental information.

This segment will focus on the use of synthetic waxes, which are the most commonly used waxes for inpainting.

Principal Name

Beeswax, paraffin, carnauba, microcrystalline wax, Multiwax, Be Square, Petronuba- C, Polywax, Victory Wax, polyethylene wax, Bareco wax, Bareco polywax, petrolatum wax, Cosmolloid, mineral wax

History of Use

1. Industrial
In addition to being used extensively in coatings and polishes, synthetic wax is used in an array of industries. Microcrystalline, for example, is used to generate such products as candles, adhesives, corrugated board, cosmetics, and castings. It is also found in the tire and rubber industries, where it is combined with paraffin to create products with greater flexibility, melting point, and opacity.

Microcrystalline wax is essential in the production of petrolatum. Different grades of petrolatum are produced by incorporating oil with wax. The properties of petrolatum are determined by the congealing point (ASTM test D938) and needle penetration depth (ASTM test D1321) of the chosen wax. In an effort to become more environmentally friendly, a hybrid petrolatum is now produced using renewable resources such as vegetable oils and waxes.

2. Conservation
In the early days of Richard Buck at Oberlin (at the Intermuseum Conservation Association), the conservators used crayons as a “quick and easy” method for temporary inpainting of paintings they saw on inspection trips. This eventually led to the idea of manufacturing “crayons” using dry pigments and selected waxes (personal communication from Martin J. Radecki, who worked with Buck in Oberlin).

Microcrystalline and polyethylene waxes are the most commonly used type of wax for inpainting. The wide variety of hardness, molecular weight, color, and refractive index makes wax a versatile material.

In addition to being used as a matting agent in varnishes and as a surface coating, it is also used as a filling and inpainting material. Combined with resin or other grades of waxes and pigments, wax mixtures can be used for filling and inpainting in one single step.

The very low shrinkage coefficient of microcrystalline wax offers advantages in the treatment of large losses and long mechanical cracks, often present in modern paintings. The opacity, tinting capacity, and handling qualities also offer many advantages in the treatment of shallow losses. Wax is also used in the treatment of panel paintings and paintings that have been wax-lined.

The high melting point of polyethylene waxes restricts their use. However, combined with softer waxes, they increase the hardness of mixtures. This can be especially useful for the treatment of works in high traffic areas, such as public art, or when a very durable coating is required, as in the case of an outdoor work.

Source

1. Physical
Synthetic wax is available in granules, pellets, beads, slabs, or liquid bulk.

2. Origin and manufacture
Microcrystalline wax was invented in the late 1930s by Baker Petrolite, Barnsdale, Oklahoma. (See Abercauph 1997 for fabrication process.)

Refining process, i.e. odor removal, bleaching, etc.

Microcrystalline waxes are divided into three categories or types: Type 1: Laminating; Type 2: Coatings; and Type 3: Hardening.

Grade	Melting point	Needle penetration (dmm°)	Properties	Applications
Type 1 Laminating	130-170F / 54.4-76.7C	20-40 dmm	Flexibility, Tacky	Packaging, Adhesives, Cosmetics, Rubber, Candles
Type 2 Coatings	170-185F / 76.7-85C	15-25 dmm	Harder, low tackiness	Adhesives, Packaging, Chewing gum, Inks, Plastics, Rubber
Type 3 Hardening	185-200F / 85-93.3C	5-12 dmm	Very hard, higher viscosity	Adhesives, Inks, Chewing gum, Candles, Speciality

° = digital multimeter"
Source: The International Group, Inc. [7]"

The standards used in the production of microcrystalline wax are the congealing point (ASTM D938), needle penetration depth (ASTM D1321), color (ASTM D6045), and viscosity (ASTM D445).

3. Manufacturers and vendors

• Manufacturers:

• Bareco. Products [8]: STARWAX™, VICTORY™, ULTRAFLEX™, BE SQUARE™ (joined Baker Petrolite under the banner of Baker Hugues)
• The International Group, Inc. [9]
• Crompton Witco

• Retailers:

• Talas [10]
• Conservation Support Systems [11]
• Museum Services Corporation [12]

Chemical and Physical Properties

(See Abercauph 1997 for additional information.)

Wax	Origin	Color	Characteristics	Composition	Melt Temperature	Hardness (Penetration)	Char	Usage	Source	RI
Beesewax	Insect Natural and bleached	Amorphous, slightly tacky (A)		147 F / 64 C 62-65 C (A)	15-20 (A)	Slab BeadⓇ	Convenient for low melting temp. Crystallizes		1.440-1.445
Be Square™ 175 amber (T, C)	Synthetic (T, C)	Amber (T, C)			175-180 F(T) 182-183 F	16-19 (T) 17
Be Square™ 175 black	Synthetic	Black		MW 500 to 800	175 F / 83 C 182 F/83 C	17	Slab		BarecoⓇ - Baker Hughes, Inc.
Be Square™ 185 black	Synthetic	Pale amber		MW 500 to 800	195 F/91 C	10	Bead		BarecoⓇ -Baker Hughes, Inc.
Be Square™ 195 black	Synthetic	White		MW 500 to 800	199 F/93 C	6	Bead		BarecoⓇ -Baker Hughes, Inc.
Carnuba	Natural Palm (A)	Amber Pale yellow to greenish brown (A)	Very hard, brittle, not tacky, lustrous (A)		180-187 F/83 C 181 F/83 C 9C) 83-86 (A)	7, 1-3 at 25 (A)	Flakes	Use sparingly. Makes wax mixtures brittle		1.4540
Cosmolloid H80	Synthetic	White		High MW purified hydrocarbon wax	166-176 F/(T)		Slab	Used extensively in Europe	Astor Corp.
MultiwaxⓇ X-145A	Synthetic	Light amber White-yellow (T)		High MW purified hydrocarbon wax	155 F/68 C, 150-160 (T)	40, 35-45 (T)	Slab		Crompton Witco
MultiwaxⓇ W-445	Synthetic	White		High MW purified hydrocarbon wax	175F/ 79 C, 170-180 F/ C (T), 170 F/C (M)	40, 28, 25-35, (T)	Slab		Crompton Witco
MultiwaxⓇ W-835	Synthetic	White	Very soft and sticky	High MW purified hydrocarbon wax	170 F/77 C, 171-178 F/ C(T), 175 F/C (M)	70, 60-80, (T)	Slab		Crompton Witco
Paraffin	Synthetic (Petroleum)	White	Soft to hard, solid, course, fibrous crystals, oily to dry (A)	High MW purified hydrocarbon wax	F/45-75 C, 44.5-74 (A)	6-40 (A)	Slab
Petronuba-C	Synthetic	Light amber	Hard, with low melting temp.	Synthetic Carnauba	199 F/93 C	7	Bead FlakeⓇ
PolywaxⓇ 500	Synthetic	White		Ethylene polymer MW 500	187 F/85 C	7	Bead		Bareco™ (Bareco poly-ethylene wax is now sold under the name PolywaxⓇ)
PolywaxⓇ 2000	Synthetic	White		Ethylene polymer MW 500	259 F/126 C, 257 F/C (M)	7, 1	Bead	Small % can be added to regular microcrystalline wax to prolong life outdoor coatings	Bareco™ (Bareco poly-ethylene wax is now sold under the name PolywaxⓇ)
Victory™	Synthetic	White		High MW purified hydrocarbon wax	175 F/79 C, 171-178 F/C (T)	26, 26-29 (T)	Slab		Bareco
Victory™ Brown		Brown							BarecoⓇ
ES692, Brown (C)	Synthetic (C)	Brown (C)	Darker and cleaner than Victory (C)		175 F/79 C (C)	26 (C)	Slab (C)

Source: This chart is provided courtesy of James Bernstein, Inpainting Workshop, May 2008.
T: Talas C: Conservation Support Systems M: Museum Services Corporation A: Carole Abercauph, citing from Encyclopedia of Polymers Science and Engineering, Vol.17, 792–93 (John Wiley and Sons, 1989).

Preparation and Formulation

1. Typical application methods
The waxes are selected depending on the nature of treatment. Some waxes can be softened with the simple action of mixing on a palette or in a hand. Others will require the use of a heat source, ranging from a mug warmer to a small hotplate.

The waxes are first mixed together to achieve a uniform mixture. The pigments can then be mixed directly into the wax or in a compatible solvent prior to being incorporated in the wax to obtain a uniform result. Solvents are used to increase malleability and working time.

The wax can be custom-tinted for a specific project or prepared beforehand in a range of colors. It can be rolled in the shape of crayons or in small squares. Caution must be taken not to exceed the melting temperature of the wax. Overheating can cause the wax to become granular. The wax can be softened or melted in a variety of ways, such as directly in your hand, on a piece of Mylar, in disposable aluminum pans, or in round metal containers. Some containers can be used for melting and storage at the same time.

2. Additives
A few drops of slow evaporating solvent can be added to increase drying time.

3. Storage/shelf life
Waxes should be stored in a cool, dry, dust-free environment. Thus stored, the shelf life is nearly infinite.

Handling Characteristics

1. Application

• Unstable cracks
• Large losses where traditional fills might crack
• Shallow losses
• Transparent surfaces

2. Modifications for special applications and effects (“Tricks of the Trade”)

Custom-made crayons are useful for inpainting unstable cracks, i.e., long running mechanical cracks in modern paintings. Pigments are ground into a soft wax such as Microcrystalline X-145A on a heated slab and then rolled into the shape of crayons. A few drops of slow evaporating aliphatic solvent can be added to increase the softness of the crayon. The color of the crayons can be customized to each project. The wax can be mixed on a palette and warmed slightly in your hand before being pressed into the crack. Excess wax can be removed with a dry cotton swab or cloth. The topography of the wax fill can be adjusted to match the surrounding original by burnishing, texturing, or altering the surface (Chris Stavroudis, personal communication July 1, 2008).

Tjanting tools (needles) are used to apply the wax in very fine lines. This rudimentary tool consists of a handle onto which is attached a circular hollow tube-like reservoir that tapers to a needle spout. The hot wax is poured into the reservoir. The tip of the tool is held down to start the flow of the wax and held back to stop it. It is available in different sizes.

Agate and silicone tip brushes can be used to burnish and texture the surface of the wax fills.

Pros and Cons of Microcrystalline Wax:

Pros	Cons
Readily Available	Certain waxes have a low Tg, can attract dirt, and should be varnished
Affordable	Color correction with another inpainting medium might be restrictive because of solubility
Chemically inert, long shelf life	Soluble in many solvents found in varnishes
Useful to fill shallow losses	Hard to wet with water and ethanol
Imparts low sheen	Does not provide a high gloss
Can be buffed to increase glass	Cannot be emulsified
Reversible with mild solvents
Does not shrink
Easy to texture
Compatible with silicone molds to reproduce fine surface topography
Available in a variety of hardness
Can be used as a fill and inpainting materials at once
Can be easily pigmented with dry pigments
Easily portable and usable for in situ treatments (crayons, palette)
Does not require the use of solvents
Chemically inert
Can be softened with the addition of mild solvents
Some waxes produce a hard and non-sticky surface
Odorless
Higher melting point (54-95°C)

Aging Characteristics

For base resin, see Abercauph, 1997.

Health and Safety

For base resin, see Abercauph, 1997.

Waxes are nontoxic materials. Precautions are advised when heating any waxes as serious burns may be inflicted by molten wax. Face and hand protection should be used when handling hot waxes. Burns should be flushed immediately with cold water. Adequate ventilation must be maintained to remove any fumes from solvents added to waxes. All waxes are flammable and must be kept away from furnaces, flames, etc.

Chantal Bernicky

Submitted November 2008

Hand Mixing Pigments in Solvent-Based Binding Media

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Principal Name

Varnish Colors

Other Names

Varnish paints, resin colors, resin paints

History of Use

1. Artistic
Varnish colors can be dated in the literature on painting technique to the mid-18th century. Robert Dossie mentioned mixing pigments with varnish without the addition of oil in his Handmaid to the Arts from 1758 and noted that “(this) art has been greatly improved and extended within these few years….” . Although he referred to shellac as the preferred vehicle for painting largely due to its durability, he stated that mastic with gum anime dissolved in spirit of turpentine could be used for whites and light colors, which would discolor when mixed with the harder resin

The influential manual on painting, gilding, and varnishing by Jean Felix Watin, which was first published in 1772, includes two recipes for varnish as a medium without the addition of oil. The first recipe is based on mastic and sandarac in equal parts and produced a medium noted to saturate colors well and dry quickly. The second, of mastic and turpentine, is said to dry more slowly but could be handled more easily and achieve a greater quality in effect.

Carlyle notes several recommendations in 19th-century artist’s manuals to reduce or eliminate the amount of oil in painting by replacing it with resins. Speed of execution due to its faster drying nature as well as less of a tendency to crack were two of the advantages that some writers noted of painting with varnish instead of oil.

2. Conservation
Perhaps the earliest mention of varnish colors used for restoration was by Pietro Edwards, the Director of Restoration of the Public Pictures for Venice from 1778 until 1819. As mentioned by Partridge in the historical overview of retouching materials in this volume, the reversibility of restoration materials was of primary importance to Edwards. This concern led him to require varnish colors to be used in the restoration of oil paintings—a directive evidenced by the oft-quoted contract for the restoration of Titian’s Assumption of the Virgin, which specified that “the parts to be repainted…shall be executed with varnish, the use of oil being absolutely excluded”

The tendency of oil retouching to darken was cited by some authors as a reason to choose varnish colors. The British manual titled Advice to Proprietors on the Care of Valuable Pictures Painted in Oil with Instructions for Preserving, Cleaning, and Restoring Them When Damaged or Decayed from 1835 notes that “…in restoring colours accidentally removed, it should be done with a vehicle of simple varnish, because of the change in tint which takes place after drying in oil” However, other restorers like Giovanni Bedotti believed resin led to rapid darkening of retouches. In his manual on the restoration of paintings from 1837, he noted that even though varnish colors were widely used in Italy, he followed the opinion more prevalent in France in favor of retouching in oil

In 1855, the Spanish artist and restorer Vincente Polero y Toledo recommended that colors for retouching be ground in mastic. He noted the difficulties in handling such a quick drying paint and recommended that the brush be constantly rewet with turpentine.

Ulisse Forni’s manual from 1866 discusses dammar varnish as a medium for restoration because it could be easily removed without damage to the painting. Although mastic could be substituted, he believed that dammar is superior and noted that it does not yellow or crack. The following year in his own restoration manual, Giovanni Secco-Suardo recognized the tendency for drained oils to discolor and wrote that the majority of (Italian) restorers used pigments mixed with turpentine and tempered with varnish.

At the end of the 19th century, the French painter Oscar Edmond Ris-Paquot mentioned in his book on restoration that varnish was a good medium for small repairs because it changes very little and is quite solid. However, he felt that it was not practicable for large losses because varnish colors dry too fast.

In the early 20th century, Max Doerner stated his preference for retouching in mastic or dammar varnish colors because they could be easily removed without damage to the painting. In addition, he noted their “transparency and saturated effect most closely approach the appearance of oil color,” but they do not discolor to the same degree.

In her review of retouching materials in the 1970s, Emile-M.le wrote that “The use of varnish paint goes right back to the late 18th century…It has always had its fans, though nowadays many of them have replaced natural resin with a synthetic product” Varnish colors continue to be used today, primarily in European countries with a long tradition of their use, such as Italy, Germany, and Spain.

Source

Dammar

1. Physical
Light blond rounded lumps of resin of varying sizes. Dammar crystals tend to have a chalky surface and become transparent/translucent when wet-up. Debris such as dirt and plant material is often found trapped in the resin.

2. Origins and manufacture
Dammar comes from the Dipterocarpus family of angiosperm trees found from India through Southeast Asia. The resin available in the United States and Europe originates primarily from Malaysia and Indonesia. The trunk of the tree is cut with incisions, and the exuded resin forms tears that are gathered after drying.

3. Manufacturers and vendors
Dammar is a common material used in oil painting and varnishing and can be purchased both in crystal form and as a varnish dissolved in solvent. Dammar crystals can be purchased from Kremer Pigments, Talas, Conservation Resources, Conservation Support Systems, among other vendors. Dammar varnish is made by a number of manufacturers of painting materials, including Winsor & Newton. It is typically dissolved in turpentine.

Mastic

1. Physical
Small light to medium honey-colored rounded “tears.” Bits of debris and dirt are sometimes trapped in the crystals.

2. Origins and manufacture
Mastic comes from the Pistacia lentiscus evergreen shrub found throughout the Mediterranean. The highest quality resin has traditionally come from Chios. Mastic tears are produced by incisions cut into the tree and the tears collected after drying.

3. Manufacturers and vendors
Mastic is not as widely commercially available as dammar. It is generally sold in crystal form. The dry resin can be purchased through Kremer Pigments, Conservation Support Systems, and other vendors. Maimeri and Kremer Pigments both make a premade varnish dissolved in turpentine.

Chemical and Physical Properties

Dammar

1. Chemical classification
Triterpenoid resin

2. Chemical formula/structure
Dammar is a complex mixture of triterpenoids and a lesser amount of polymeric material of which the exact components and percentages can vary. The tetracyclic dammarine skeleton series comprises the largest portion of the resin but also present are pentacyclic oleanane, ursane, and hopane derivatives

3. Solubility
Initially soluble in turpentine, xylene. As the resin ages, more polar solvents are required for its removal.

4. Tg
Approximately 39°C

Mastic

1. Chemical classification
Triterpenoid resin

2. Chemical formula/structure
Mastic is a complex mixture of compounds including triterpenoids of the tetracyclic euphane and dammarane skeleton type as well as the pentacyclic oleanane skeleton type. Two bicyclic triterpenoids have been identified in analysis as well.

3. Solubility
Initially soluble in ethanol, acetone, turpentine.

4. Tg Approximately 35°C

Preparation and Formulation

1. Typical preparation
The following procedure is used at the Opificio delle Pietre Dure in Florence, Italy (Irma Passeri, personal communication, 2006): One part mastic resin is dissolved into three parts turpentine. The solvent is then allowed to evaporate until the medium reaches a honey-like consistency. Pigments are prepared by grinding on glass with water and a little ethanol, left to dry, and then stored in containers. The varnish is mixed into a small amount of pigment with a spatula to form a smooth paste. Some colors require more medium than others, but care is taken not to add too much varnish, which would render them too transparent. The varnish colors are set out on a palette, and the solvent is allowed to evaporate off. Xylene and, more recently, ethyl lactate (ethyl 2-hydroxypropionate) with a little isopropanol added to speed drying are used as diluents.

2. Additives
In the past, Canadian balsam has been added to the medium to help the paint form a paste. However, it has fallen out of favor at the Opificio because it becomes too hard and reduces the solubility of the varnish colors.

3. Storage/shelf life
A palette of varnish colors does not have a finite shelf life and will remain resoluble indefinitely. Because the paints are fairly soft, the palette should be covered when not in use to avoid dust.

Handling Characteristics

1. Application
In Florence, varnish colors are applied in a tratteggio technique on a base of watercolor or tempera that has been applied in a flat tone. They can be layered but care must be taken with the amount of diluent used because the underlying strokes can be disturbed.

2. Appearance
Due to their transparency and refractive index, varnish colors can be used to great advantage to simulate an aged oil paint as well as a patina.

3. Modifications for special applications and effects (“Tricks of the Trade”)
More medium or diluent can be added to the mixed colors to adjust their opacity. Maimeri colors enriched with more varnish medium are sometimes used if specific colors are needed that are not available as dry pigments.

Aging Characteristics

1. Chemical process
The precise mechanisms of the aging of mastic and dammar films are complex due to the number of compounds that compose these resins. The aging process is based on autoxidative free radical chain reactions primarily initiated by exposure to ultraviolet light. After the primary autoxidation reactions, thermal processes lead to secondary degradation reactions.

2. Resultant chemical and/or physical alterations
The aging process leads to an increase in molecular weight, the formation of polar degradation products, and the formation of yellow and fluorescent products.

3. Impact on appearance, solubility and removability
The increase in polar degradation products in an aged resin results in the need for more polar solvents to be used in its removal. The formation of yellow chromophores can lead to significant yellowing of the medium over time. Other autoxidative reactions can lead to brittleness, hazing, and loss of gloss.

4. Attraction and retention of dirt and grime
Dammar and mastic resin paints do not seem to preferentially attract or retain dirt and grime.

5. Theoretical lifetime
When used in thin layers and in dark passages, the inpainting should last as long as the varnish in a typical restoration.

Health and Safety

Mastic and dammar dry resins do not present a health hazard. The dust from dammar resin can be a respiratory irritant in high concentrations. The MSDS should be followed for the solvents used to dissolve the resin.

Disposal

There are no special precautions to take if all the solvent has evaporated.

Elise Effmann-Clifford

Submitted July 2006

Hand-Mixed Acrylics

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Although most acrylic resins that are used by painting conservators as varnishes have also been employed as inpainting media, ParaloidⓇ B-72 is the acrylic resin that is most commonly used for inpainting. Therefore, this section has been written based on the author’s knowledge of and experience with B-72. For information regarding principal names, history of use, source, chemical and physical properties, aging characteristics, health and safety factors, and disposal, see Volume 1 of the Painting Conservation Catalog: Varnishes and Surface Coatings and go to[13]

Preparation and Formulation

1. Typical application methods
Paraloid B-72 can be ground with dry pigments for use as an inpainting medium. A typical stock solution is 20 percent B-72 solids (weight/volume) in either xylenes or propylene glycol monomethyl ether (methoxy proxitol) (Arcosolv PMⓇ). The pigments should be ground into this mixture so that each pigment particle is fully dispersed and coated with medium. This can be accomplished either directly on the palette with a small spatula or in larger batches using a mortar and pestle. The paint can be diluted with the solvent used in the preparation of the stock solution to create a more matte appearance. To increase glossiness, more stock solution can be added or a stock solution with a higher concentration of resin can be used.

2. Additives
Additives are not commonly used because the level of glossiness can be modified by adjusting the type and amount of diluent used.

3. Storage/shelf life
Paraloid B-72 is a Class A material, as rated by the standards established by Robert L. Feller . This means it remains stable for perhaps 200 years if stored and used in a museum environment.

Handling Characteristics

1. Appearance
Paraloid B-72 has a tendency to have a fairly matte, unsaturated appearance. This can be adjusted by adding more medium or by using a medium with a higher concentration of resin. It can have a grayish cast, especially when mixed with dark pigments.

2. Modifications for special applications and effects (“Tricks of the Trade”)

• It is important to saturate the pigments fully to avoid graying and muddiness. Dark pigments will require more medium.
• High chroma pigments can be used to help compensate for Paraloid B-72’s tendency toward grayness.
• Keep pigments, brushes, and medium clean to aid in achieving the darkest darks and whitest whites.
• To prevent muddiness, it is often beneficial to build up numerous transparent layers to create opacity.

Jim Bernstein recommends the following three diluent solutions:

1. To create a more matte finish:

Heptane 70 ml

Toluene 30 ml

1. For a slow evaporating diluent:

Petroleum Benzine 45 ml

Isopropanol 30 ml

1-Methoxy, 2-Propanol 10 ml

Shellsol 15 15 ml

Acetone 20 drops

Benzyl Alcohol 5 drops

1. For normal evaporation:

Petroleum Benzine 70 ml

Xylenes 30 ml

Acetone 25 drops

Benzyl Alcohol 5 drops

Bernstein points out that the presence of xylene assists in staying close to the solubility center of most conservation resin paints, and he cautions users not to use a lot of xylenes when inpainting over resoluble low molecular weight varnish.

Joanna Dunn

Submitted February 2010

Hand-Mixed Poly (vinyl acetate) Resins

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Poly (vinyl acetate) (PVAc) resins have been employed in artists’ paint since the 1930s (Clark and Ives 1935). Restorers have also employed them for inpainting. PVAc resins have been in use both to formulate paints in the studio and in ready prepared form from colormen. Their main use in conservation has been in the formulation of a medium by dissolving the resin. Progressive thinning of the solution with ethylene glycol monoethyl ether or cellosolve acetate results in a versatile vehicle capable of a wide range of matte and gloss finishes. Alternatively, the solution may be thinned with alcohol with a few drops of ethylene glycol to increase drying time. Cohesive, adhesive paints may be formulated with a medium containing less than 5 percent solids, although 10 percent is required to imitate oil paints. The refractive index of PVAc (c. 1.46-7) requires it to be glazed with resins of higher RI to imitate richly bound oil paints.

In many respects, poly (vinyl acetate) works and appears like whole egg tempera, although it may not hold textures as easily as an egg. Compared with many of the resins we use in conservation, the lower molecular weight PVAcs are notoriously low in Tg and creep, which may be an issue for some environments or applications. PVAcs of varying sizes may be mixed to achieve the wetting properties and firmness desired. For more information on poly (vinyl acetate) resins, see Gettens and Stout’s Painting Materials: A Short Encyclopedia ; the table in UNESCO, The Conservation of Cultural Property ; Mastering Inpainting Workshop Manual by James Bernstein and Debra Evans; and the chapter on PVAc in Volume I of the Painting Conservation Catalog: Varnishes and Surface Coatings (Painting Specialty Group 1998 [14])

One of the most commonly employed PVAc resins in inpainting today is MowilithⓇ 20, which closely approximates the molecular weight and properties of Palmer CementⓇ, or Vinylite AYABⓇ, formerly a favorite for inpainting formulations. Mixing 1 part AYAAⓇ with 1 part AYACⓇ can also result in a similar molecular weight resin. The author is familiar with the use of Mowilith 20.

Principal Name

Mowilith 20

Other Names

Lascaux Medium for Retouching., Berger’s PVA Inpainting Medium.

History of Use

1. Industrial
See the varnish volume of the PSG catalog.

2. Conservation
Mowilith was adopted for use by several conservators as a substitute for PVAc AYABⓇ after production of that resin, also sold as Palmer Cement, was discontinued.

Source

1. Physical
Mowilith is available as a translucent resin or dissolved in a solvent (e.g., Ethanol/Acetone or methyl proxitol).

2. Origins and manufacture
See the varnish volume of the PSG Catalog.

3. Manufacturers and vendors
Lascaux Medium for Retouching, Talas Berger’s PVA Inpainting Medium, Kremer Mowilith 20.

Chemical Properties

1. Chemical classification
Vinyl Acetate

For its chemical formula and structure, solubility, and Tg, see the varnish volume of the PSG Catalog.

Preparation and Formulation

1. Typical application methods
Mowilith is generally prepared as a solution in either ethanol, a mixture of ethanol and acetone, ethanol with cellosolve or cellosolve acetate, or in propylene glycol monomethyl ether (ArcosolvⓇ). The solutions are generally made to be of a viscosity resembling the paint to be emulated in the retouching. Typical formulations range from 8 percent to 30 percent solids. The solubilized resin is mixed with dry pigments, often directly on the palette. Additional resin or diluent can be added to the dried colors to achieve the desired level of gloss. At the 1990 IIC conference in Brussels, Gustav Berger discussed the use of PVAc as an inpainting material, with a reference to substituting Mowilith for PVAc AYAB.

2. Additives
Because the gloss and handling properties are readily manipulated by the type and amount of diluent utilized, additives are not commonly used.

3. Storage/shelf life
Experimental tests of PVAc have shown it to be a very stable (Class A) material. Mowilith will fuse into a solid block, which must be shattered into smaller pieces to make it dissolve more quickly in the diluent.

Handling Characteristics

1. Appearance
Depending on the ratio of solvent to resin, Mowilith can have characteristics ranging from a matte scumble to a rich resinous glaze. Altering the amount of pigment in the mix can result in effects from opaque films to spare dispersions.

2. Application
The most common application method is with small inpainting brushes. The medium can also be thinned with solvent and applied as a spray coat to seal underlayers.

3. Modifications for special applications and effects (“Tricks of the Trade”)
If Mowilith is diluted in pure propylene glycol monomethyl ether, it can be manipulated for a longer time, allowing blending and glazing effects. The use of ethyl alcohol as the solvent makes it dry more quickly and allows the conservator to keep the color more matte and each brushstroke distinct. Jim Bernstein recommends the following solvent mixture:

Ethanol 95 ml

Diacetone Alcohol 5 ml

Acetone 15 drops

Benzyl Alcohol 5 drops

Gustav Berger’s publication describes various handling characteristics to achieve specific ends, such as final glazes, cracks, and the creation of patina using watercolor or varnish colors over the PVAc.

Catherine A. Metzger

Submitted May 2004

Proprietary

Aqueous Binding Media

The author for this chapter on watercolors uses the SchminckeⓇ line of products and thus has written the entry based on experience and knowledge of Schmincke. Although there are numerous manufacturers of watercolors, as the material properties of watercolors will remain consistently those of pigments mixed in water-soluble vegetable gum, the entry stands pars pro toto for all watercolors. It should be noted that each product line will have differing pigments, pigment-to-gum ratios, and lightfastness, etc.; practitioners should acquaint themselves with the variant handling of the manufacturer’s line before investing in a complete set of paints. In addition to researching each manufacturer’s information, other sources may also be useful. One such online source is Handprint [15], a single artist’s site based on his personal tests, observations, and biases solely as a user of watercolors.

Watercolors (Plant Gum)

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Principal Name

Schmincke watercolors

Other Names

Schmincke HoradamⓇ Aquarell, HoradamⓇ Watercolors, Schmincke AkademieⓇ Aquarell

History of Use

1. Industrial/Artistic
Founded in 1881 by two chemist-colormen, H. Schmincke and J. Horadam, the Schmincke factory originally produced natural-resin oil colors for artists. Josef Horadam developed the watercolor line of products and received his first Prussian patent in 1892 for “Horadam Patent-Aquarellfarben.” Although Schmincke does not specify its research methods, the company states that it continues to research and develop artists’ materials, striving for the highest standards of quality and service, including consumer outreach through its Internet site [16].

2. Conservation
Pigments in a gum binder have long been available to artists, the earliest restorers, and modern conservators. By way of documenting the use of watercolors in the early eras of modern conservation, Morton Bradley in his Treatment of Pictures noted, “A water emulsion of poly (vinyl acetate) may be added to water-color paints for use over a resin coating.” The 1987 completion of the conservation treatment of Diego Rivera’s Detroit Industry included the decision to use watercolors for inpainting due to the compatibility with the original surface, ease of removability, and lack of toxicity . Depending on the surface to be inpainted, watercolors are most often used alone or as a preparatory layer for glazes or other inpainting media With this great range of versatility, watercolor has proven to be a useful tool in conservation.

Source

1. Physical
Schmincke watercolors are available in ready-to-use 5ml, 12ml, and 15ml tubes, or in half or full pans.

2. Origins and manufacture
Schmincke follows a traditional liquid pouring of watercolors in pans, which is carried out sequentially four times using special machinery. Company literature states that after each layer, the pans are placed in drying chambers to dry at constant temperature for 2–6 weeks, requiring a total production time of 3–5 months for a single pan. This unique process enables the company to use the same formula for both pan and tube colors—and enables the user to fill pans with tube colors when necessary. Schmincke watercolors conform to ASTM D-4236 (Schmincke n.d.), which is a mandatory U.S. health labeling standard (Gottsegen, personal communication, 2009).

3. Manufacturers and vendors
Schmincke watercolors, Horadam Aquarell, Horadam watercolors, and Schmincke Akademie Aquarell are manufactured by H. Schmincke & Co. and are distributed by artists’ supply stores. [Although the ASTM International’s subcommittee on artist’s materials recommends using brands that conform with ASTM D-5067—the Standard Specification for Artists’ Transparent Watercolors —it cannot be confirmed, as of this writing, whether the manufacturer Schmincke conforms to this ASTM standard.]

Chemical and Physical Properties

1. Chemical classification
Pigments are bound in a non-crystalline plant-based gum. The plant gum is composed of salts of organic acids built of sugar units with Ca, Mg, and K

2. Chemical formula/structure
Kordofan gum arabic with pigments, extenders, additives, and water. The listed pH values for the watercolors are pH 5–6.5 at 50% concentration and 20°C.

Shades 223, 224, 225, 226, 227, 228, 347, 348, 349, and 350 contain Cadmium pigments. Shades 487, 488, 499, 509, 510, 533, and 535 contain Cobalt pigments. Shades 209, 212, 530, 536, 221, and 229 contain Nickel pigments. It is known that different pigments require different amounts of gum to function well so exact formulas vary, but Schmincke watercolors are known for having a high pigment-to-binder ratio.

3. Solubility
Soluble in water and miscible in all proportions.

4. Tg
Not available

5. Pigment and content labeling
Names of individual colors in the Schmincke Horadam (and other manufacturers’) watercolor lines are often not indicative of the pigments or mixture of pigments used in individual watercolor paints. Minimally, the manufacturer should provide the Pigment Index information for the colors present (e.g., PY 154 or PG 36). The conservator should obtain the technical product literature available from the manufacturer for the most complete listing of watercolors available by a manufacturer, the actual pigments or mixture of pigments present in each color, and some indication of lightfastness (LF) rating (with the caveat that a paint seller is in the business of selling paints, so almost all pigments are going to have a somewhat acceptable LF rating, according to the maker).

The conservator should know the content and permanence of each color used in the palette. The manufacturer naming may be misleading. For instance, Schmincke provides a color #786, Charcoal Grey. Referral to the product literature indicates that the paint contains no charcoal; it is, in fact, Lamp Black PBK 7. The paint is fine for the conservator to use if he or she understands that it is Lamp Black, but it will not produce any of the special effects that a true Charcoal Black will provide.

Also, the manufacturer may provide some colors for artist interest, but not all pigments will be suitable for conservation use.

Watercolor White Pigment Caveat

Conservation scientist Robert Feller established as early as 1955 that retouchings containing Zinc White (Zinc Oxide PW 4) deteriorated prematurely, causing chalking (whitening/break-up) of inpaints in resin paints (PVAcs, Methacrylates, etc.). If watercolor underpainting is subsequently glazed with resin colors and resin varnish (as it often is in traditional easel painting restoration) and zinc oxide is present in the underpainting, this bodes poorly for the stability of underlying glazes. Chinese White (Zinc Oxide White), although present in many watercolor paint sets, should never be used when resin glazing or varnish is to follow. Zinc White may be considered for use if applied as a standalone application where the white color is not to be mixed with other colors or coated (Bernstein, personal communication, 2010). For further information on Zinc Oxide, refer to Artists’ Pigments: A Handbook of Their History and Characteristics, Volume 1

Preparation and Formulation

1. Typical application methods
Application is most typically by a wet to damp brush (although airbrush has been used).

2. Additives
Schmincke watercolors contain ox gall, glycerin, sugar syrup, and dextrin. According to Dr. Müller, a representative of H. Schmincke & Co., they do not contain paraformaldehyde (personal communication, 2004), an ingredient in some watercolor preservatives that may be of concern, as noted by Rossol

3. Storage/shelf life
The shelf life of tubes is three years; for pans, more than five years.

Handling Characteristics

1. Appearance
The form is pasty, the color depends on ingredients used but is uniform, the odor is slightly aromatic, and the flow properties are excellent. In addition to rating colors for lightfastness (stars) [that does not correlate with ASTM D-5067 ], Schmincke also rates colors for glazing/opacity properties (squares) and for staining properties (triangles)—symbols noted on package labels—along with color index number and color name.

2. Application
Application techniques vary from washes to layering, from the vertical hatch strokes of tratteggio (rigatino) to the contour interweaving of colors (cromatica astrazione or cromatica selezione) to pointillist style.

Traditionally, watercolor is a fundamentally transparent medium, used to achieve transparent effects. The thin applications of color are made luminous by the bouncing of light off the underlying white paper or chalk/gesso. While some pigments in watercolor are opaque, there are limitations of watercolor imitating full-bodied, pigment-rich paints, such as acrylic dispersion colors or silkscreen printing inks. For these, pigments in AquazolⓇ Or gouache may offer more of the body and the desired, densely pigmented look of certain paint structures.

3. Modifications for special applications and effects (“Tricks of the Trade”)

i. Addition of gum arabic to increase transparency .

ii. Addition of AquapastoⓇ, a Winsor and Newton tube formulation of gum arabic thickened with silica, to mimic texture/brushwork. Aquapasto and gum arabic solutions, in general, darken with age and so should be used with caution. Addition of gum arabic or Photo-floⓇ to aid in adhesion to nonabsorbent surfaces (Elyse Klein, personal communication, 2004).

iii. Especially good for adding fine cracks on top of PVAc or MSA inpainting, adding a bit of “dirt” quieting abrasions before varnishing (Joyce Hill Stoner, personal communication, 2004).

iv. For transparent glaze effects, seal watercolor base with varnish then use diluted MaimeriⓇ or Gamblin Conservation Colors (pigments in LaropalⓇ A81) as a glaze (Heller, personal communication, 2004).

v. Add small amounts of either gum arabic or calcium carbonate for gloss and matte respectively. Use only as much water as necessary to keep paint workable and for less value distortion upon drying (Peter Malarkey, personal communication, 2004).

vi. Silicates, available in many shapes and sizes, are among the clearest particles (glass-like) and are better matting agents than calcium carbonate (chalk), which imparts milky whiteness/turbidity to colors Note that caution should be taken when considering the use of silicates as free silica may be present and pose a health risk.

vii. Use “Water Extra-Dry” (adding some acetone to water) to speed drying and provide greater control of paint application. This also aids in reducing surface tension and pigment dispersion (especially when organic-origin or “greasy” pigments, such as Lamp Black, are present) for improved paint mixtures, particularly when bits of dry pigment are added to proprietary watercolors.

Starting-point formulas are ⁸:

Deionized Water	70 ml
Acetone	30 ml

or

Deionized Water	60 ml
Acetone	40 ml

The exact percentage of acetone to water will depend on:

• The artwork under consideration;
• The application requirements;
• The ambient temperature and humidity;
• The size of the brush being used.

Alternately, adding ethanol to water (“Waternol”) may also break down surface tension and improve wetting. Formulas are as follows:

Deionized Water	75 ml
Ethanol	25 ml

or

To break down surface tension, improve wetting, and reduce the amount of water being used, the formula below is suggested. It also lowers viscosity and improves handling of paint binders such as Aquazol that may be unwieldy in water alone.

Deionized Water	50 ml
Ethanol	50 ml

viii. Use of gum arabic as a medium for grinding watercolors: The conservator may prepare custom watercolor paints for his or her use for access to the fullest range of pigments, producing paints of maximum purity and intensity and in colors not readily or otherwise available commercially. As a cautionary point on gum arabic preparation and usage, do not use traditional ox gall as a wetting agent or certain proprietary gum arabic mediums containing acetic acid as both are pH 5 or below. As preparing gum from dry tears of the resin is very time consuming and difficult (requiring extensive filtration), use only the finest grade prepared gum arabic solution (e.g., Winsor and Newton). Bernstein recommends grinding the pigment in water with some acetone first, then slowly adding the gum arabic solution. Test the paint swatch, allowing it to dry to determine the correct pigment-to-medium ratio.

Bernstein provides the following formula as a starting point:

Winsor and Newton Gum Arabic 96 ml

Glycerin 4 ml

Honey:water (1:3) 5 drops

Golden. Universal dispersant 1-2 drops

(of 10% GUD diluted in water)

Aquazol. 50 solution 2-5 drops

(from 35 gms Aquazol in 65 ml H2O)

ix. Add trace amounts of Titanium Orange (Chrome Orange Titanate), ocher, or cadmium orange to warm light-value colors and to counteract “cold” white, especially when covering dark spots Mohr 2004.

x. Watercolor with the admixture of a small amount of Lascaux 498HVⓇ will make the watercolor more resistant to water but will still allow it to be easily removed with water or saliva and a bit of pressure on the swab. Aquazol 200Ⓡ has also been mixed with watercolor to inpaint a loss on a contemporary oil painting with a high wax content, providing a good gloss match (Tomkiewicz, personal communication, 2004; 1999).

xi. When using watercolor for transparent toning or inpainting on porous modern paint structures (exposed canvas, Color Field Acrylic paintings, etc.): Watercolor should never be used directly on open canvas or porous structures where intractability and irreversibility may be an issue. Watercolors are known to become increasingly insoluble with age; if used directly, they may travel into a painting structure, producing permanent staining and optical alteration of adjacent original paint or support. Exposed canvas, paper, or other cellulosic supports—often disrupted and made more porous due to physical deterioration or damage— need to be relaxed and re-swollen with gradual humidification. The temporarily plasticized fibers/threads/wood particles may then be coaxed, realigned, and brought back into plane to simulate the original or former topography.

Once all fiber manipulation has taken place, a dilute adhesive may be introduced, if appropriate, to consolidate the region. To counteract excessive porosity in a region of disruption and repair, the application of a dilute isolating size is recommended before applying any color.

One of the most benign and effective cellulose isolators prior to inpainting with watercolors is a thin, continuous application of sodium carboxymethylcellulose ether (gum) size. Depending on the artwork and isolation requirements, the conservator may select one or a mixture made from the following stock solutions:

Methocel A4C (mw 41,000 viscosity 400 cps) 3.5% in water

Methocel A15C (mw 63,000 viscosity 1500 cps) 2.5% in water

Methocel A4M (mw 86,000 viscosity 4000 cps) 2.5% in water

Stock solutions need to be diluted with additional water for application. The lower viscosity grades offer greater flow; the higher viscosity grades are more unwieldy to apply but offer more skin-like isolation.

xii. Use of increased air flow or increased warm air flow may aid in applying and working with watercolor: Under typical studio conditions, watercolor paints in water take a few minutes to dry. This can be problematic, as the exact final color of the dried paint may only be observed a few minutes later, slowing down the inpainting process. Drying may be accelerated if freshly applied watercolor retouchings are gently blow-dried with a small portable hair dryer (with the heat setting turned off). If more rapid drying is required and the artwork allows it, blow-drying from a distance with the blower set to mild heat may be employed. In some instances, it is beneficial to “pre-dry” an artwork structure before inpainting with watercolor. The blow dryer may be directed to a place on a stretched canvas (e.g., Color Field painting) to “pre-desiccate” the porous canvas structure. After preparing the canvas in this manner, tiny bits of watercolor in “Water Extra Dry,” applied with a tiny brush, may be applied to the desiccated surface and the color may be placed with little or no wicking or traveling.

xiii. Making watercolors more viscous, controllable, resoluble, or plastic: Watercolors in water by themselves are very fluid and difficult to control. A tiny trace of gum from a sodium carboxymethycellulose solution (e.g., MethocelⓇ A4C) may be introduced into the watercolor. This will extend and distribute the pigment particles further apart, making the paint more viscous, less intense, and less staining—in essence, more controllable. Color and design may be built up with successive applications of paint, each containing less cellulose gum. The cellulose gum also aids in reversibility, enabling future re-swelling and clearing away of aged watercolor retouchings with water.

xiv. In addition to sable rounds and other brushes traditionally used for watercolor painting, the conservator should become acquainted with “Spotters.” Spotters or retouchers are a squatter version of the pointed round sable brush. The shorter hair length and rapid tapering to a point make them very effective in some inpainting instances. The squat brush form prevents the hairs from flopping (as may happen with long haired rounds) and there is less of a belly on the brush, so amounts of paint delivered to the tip may be more controllable. They are particularly effective for slippery surfaces or “spotting” activity, where the color is applied head-on as a dot, rather than laid linearly as a stroke. One consistently excellent version of the spotter is the Winsor and Newton Series 7 Miniature Kolinsky sable. watercolor brush, available in a variety of sizes.

Aging Characteristics

1. Chemical process
Lightfastness tests are conducted on finished colors; colors are rated with a five-star system correlated to the blue wool standard (blue scale 3–3.5 = 1 star least lightfast/less than 20-year lifetime; 3.5–5 = 2 stars limited lightfastness; 5–6 = 3 stars lightfast; 7 = 4 stars good lightfastness 100+ year-lifetime; 8 = 5 stars extremely lightfast). [It should be noted that although the blue wool scale is still commonly used, it might be inaccurate according to the two major lightfastness-testing companies: Atlas Materials Testing and QLab. ].

2. Resultant chemical and/or physical alterations
Fading for fugitive to limited lightfast colors with (extended) exposure to light.

3. Impact on appearance, solubility, and removability
Fading of some colors possible, some colors may stain, colors generally remain soluble in water.

4. Attraction and retention of dirt and grime
Information not available.

5. Theoretical lifetime
This depends on particular pigments’ lightfastness, e.g., a color with five stars has a theoretical lifetime of between 150 and 200 years under “museum conditions” (Müller, personal communication, 2004).

Health and Safety

(See varnish chapter for base resin)

• Flash point: not applicable

• Slight irritant to eyes

• Non-sensitizing

• Moderately/partially biodegradable

• Use general protective and hygiene measures (do not eat, drink, or smoke while using; avoid contact with eyes).

First-aid

• Eye contact: rinse thoroughly with water, seek medical advice if symptoms persist.

• Skin contact: clean with soap and water.

• Inhalation: remove from exposure.

• Ingestion: in case of problems, seek medical advice and show package label.

Hazards

The shades containing Cadmium, Cobalt, or Nickel pigments contain chemicals known to the state of California to cause cancer by means of inhalation.

Disposal

Do not discharge into waterways; retain and dispose of contaminated wash water. Classified as nondangerous goods, the product does not require hazard warning labels in accordance with EC directives. Empty packages may be recycled.

Victoria Ryan

Submitted December 2004

Gouache

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Principal Name

Gouache is a term for opaque watercolors. It therefore describes a visual effect rather than a separate class of materials. Opacity is achieved through adding a higher proportion of pigment than is used in watercolors and sometimes by the addition of an inert substance, such as blanc fixe (CaCO3), that gives the colors opacity. Gouache is gum-bound and remains water-soluble when dry.

Other Names

The term gouache is French, but it derives from the Italian word guazzo, meaning muddy pool or bog, or perhaps guazza, meaning dew or moisture. There is no equivalent English term, “apart from the commercially tainted ‘poster colour’ (which tends in fact to be made of inferior ingredients)”. Gouache may be designated as “Designers’,” “Fine Artists’,” or “Student or Beginner grade.” Designer gouaches are tubes of color, available in a wide range of colors, which are consistent pre-mixed combinations of several different pigments for use where permanence may not be mandatory. In fact, many of the bright colors have “been observed to fade completely in less than a year of exposure to sunlight. “Fine Artist” gouaches come in a more limited range of colors, and the tubes may contain only a single pigment. Student or beginner grade gouache is of more variable quality than these other types, and it may contain inferior pigments, binding agents, and other additives. Products called “Acrylic Gouache” are not true gouache. Although it is matte like gouache, it does not remain water soluble when dry, and the binder is an acrylic resin rather than a gum.

History of Use

1. As an artist’s material
Since gouache is essentially watercolor with the addition of opaque inerts, its history of use is not easy to separate from that of its more transparent cousin. Theophilus, writing in the 12th century, describes the use of gum binders, and there is evidence that it was a common medium in ancient classical painting. It became the dominant pigment binder in Europe during the 14th century, since it was better able than the previously used glair to saturate certain pigments, especially dark blues. The use of exclusively opaque watercolors did not develop until the late 18th century in Europe , although gouache was used for Indian miniature painting before that date. Gouache became increasingly popular in the 19th century due to advances in color chemistry that allowed the development of new opaque inorganic pigments in a much wider range of colors.

2. First conservation use
While the tradition of using watercolor or gouache for restoration may predate the 20th century, its use in previous centuries cannot be confirmed, since pre-20th-century sources describing restorations in aqueous media do not specify whether that medium is tempera, watercolor, gouache, or glair. As late as 1914, an essay by a restorer working in Germany and Latvia described the use of water-based retouching with varnish glazes over it , but it is unclear what the specific medium is. In 1939, an official museum publication in France—Manuel de la Conservation et de la Restauration des Peintures—recommended tempera paint or pigments mixed with rabbit skin glue as the lower layer in a two-part inpainting system , so it is clear that gouache was not the primary aqueous medium in conservation use at the time. However, once gouache became widely available in tubes, during the 1930s, it might have begun to replace handmade tempera and glue colors due to its convenience.

Currently, gouache is a common component in two-part systems of inpainting in which the gouache forms a base layer that is modified by an upper glaze layer. This system, especially popular in Europe, has been taught for many years at the Belgian conservation program at l’Institut Royal du Patrimoine Artistique (IRPA) and is in use in Germany (Tomkiewicz, personal communication). In the United States, Mark Leonard described its use as an inpainting material on an Italian Renaissance painting at the 2003 Yale Symposium “Early Italian Paintings: Approaches to Conservation” , and it was used by Tiarna Doherty in the treatment of an Oudry painting in 2007 (GCI n.d.).

Source

1. Physical
As in transparent watercolor, the historic binder for gouache was cherry gum or gum arabic (also called gum acacia), an exudate of the acacia tree, but neither is a precise term. Cherry gum also included the gums of the apricot, almond, peach, and plum trees. Modern gouache is bound with gum arabic, most commonly derived from the Senegalese acacia.

2. Present-day vendors
In 2009, at least 12 companies offer gouache paints, usually in 15–20 ml metal tubes, although they are sometimes available in pans or bottles. The claims listed below for these paints are extracted from promotional materials and have not been lab tested (for independent information on stability, see “Aging Characteristics” below). Since gouache is more compatible with titanium than zinc (Chinese) white, the companies that carry titanium are noted below.

• Daler-Rowney “Designer’s Gouache”: Available in 87 colors, milled “up to 9 times.” In business since 1783, the company caters to fine artists. The opacifier is calcium carbonate. The company offers both Chinese and Titanium white. The color chart available on their website lists the color index number (but no chemical name of the pigments), four levels of lightfastness, and a cursory opacity rating. (UK)

• Da Vinci: A small company whose high-quality colors all conform to the stringent ASTM D5724 standard. The technical sheet on their website identifies all colors by pigment name, CI name, and CI number and gives a lightfastness rating. The company offers titanium white only (no zinc). (USA)

• Holbein Artists’ Gouache: 90 colors, no opacifiers added. (They also offer an “Acryla” gouache series, which is resin bound and therefore not a true gouache.) They provide a color chart with three levels of lightfastness and the pigment name. They offer zinc white and permanent white, which is titanium dioxide. Their paints adhere to the stringent ASTM D5724 standard (see “Aging Characteristics” below). (Japan)

• M. Graham Gouache (artists’ gouache): This small company catering to fine artists makes 38 gouache colors, mostly based on a single pigment. The binders are gum arabic and honey (added as a plasticizer), which they claim create a smoother finish. No fillers or opacifiers are added. Their website includes a color chart with three levels of lightfast ratings, four levels of opacity ratings, and listings of the chemical name of the pigment and color index number for each pigment. They do not offer zinc white as a gouache pigment (probably because of its instability in gouache); both their Chinese white and titanium white are made with titanium dioxide. (USA)

• Schmincke Horadam (artists’ gouache): No opacifiers added. They offer three grades of gouache; the highest grade for fine artists is available in 48 colors; all but eight are pure pigment (no mixtures). The other grades are designer’s gouache (60 colors) and Academie, a beginner’s grade with 18 colors. They publish their own MSDS and color chart. They claim that all their colors except for madder lake deep (color #12354) meet the ASTM D5724 standard. They offer a permanence rating chart that they claim is more rigorous than the ASTM standard. They use a different opacity rating than the ASTM standard because their definition of opacity is not the same as the ASTM’s. They offer titanium and zinc white. (Germany)

• LeFranc et Bourgeois (Designer’s Gouache): Linel gouache, 40 colors. (France)

• Maimeri: 54 colors. The company offers both titanium and zinc white and supplies a rating chart with two levels of lightfastness and opacity. (Italy)

• Winsor and Newton “Designer’s Gouache”: No opacifiers added, available in 84 colors. They offer extensive technical information about their gouache. Their color charts identify colors by specific pigment name, color index name, and color index number. They assess four levels of lightfastness and also indicate relative opacity, as well as which paints will granulate, stain, or bleed. They offer titanium white and zinc white, but do not recommend titanium white for mixing with other pigments. They suggest using only AA- or A-rated colors if permanence is important. (UK)

• Reeves: Reeves lists sets of 12–24 tube colors on their website, but no materials information is included. (UK)

• Savoir Faire: The company markets “French School Gouache,” but no materials information is included. They also offer Lascaux “Acrylic gouache,” which is not true gouache. (USA)

• Royal Talens extra fine gouache: 60 colors, available in tubes or bottles, two whites offered (no pigment names given), lightfastness chart on website. (Holland)

Chemical and Physical Properties

See watercolor entry (III.B.1.a).

Preparation and Formulation

1. Commercial manufacture
Commercial manufacture of gouache began in the 19th century, with the production of a limited range of colors, including lead white, red lead, chrome yellow, copper oxide green, Naples yellow, and cobalt blue. In 1841, the old-fashioned pan was replaced by metal tubes and by 1851, Winsor and Newton had created “moist watercolors” of thicker consistency that could be stored in tubes. This led to the addition of extra gum binder to these paints, since they were often applied more thickly and would otherwise crack or look too chalky.

Poster color appeared after World War I. Further improvements led Winsor and Newton to introduce their line of gouache in 1937. At present, there are at least twelve companies making it. It is prepared by the same method as watercolor, but it is made more opaque by the addition of greater amounts of pigment or sometimes by the addition of opacifiers. Modern commercial preparations of gouache usually include gum arabic, wheat starch (dextrin), preservatives, thickeners, plasticizers, and wetting agents. Plasticizers may include hydromel or sugar water, and glycerine may be added to keep the paint moist (Mayer, as quoted in Schenck 1994, 17). Opacity is generally achieved by the addition of precipitated chalk, although some higher-quality gouache manufacturers claim that no white is added to boost covering power and that the opacity is due purely to the amount of pigment present in the binder. Cheaper grades may use lithopone (zinc sulfide with barium sulfate and titanium dioxide) as the opacifier. In general, gouache is bound with a slightly higher proportion of gum than watercolors, and its pigments may be less finely ground. Its solubility is the same as that of watercolor; it remains water soluble once dry.

2. Pre-commercial formulation
Before commercial manufacture, gouache was made in the same way as watercolor (see watercolor entry in this catalog, section III.B.1.a.), with the addition of opaque white.

Handling Characteristics

1. Appearance
When dry, gouache appears as a matte opaque layer with little or no impasto. Unlike watercolor, it dries lighter than its color when wet. This is because the chalk additive is translucent when wet but opaque white when dry ; conversely, it darkens appreciably when varnished. It must be also due to the relatively greater amount of pigment in proportion to medium because the higher-grade gouaches do not add opacifiers.

2. Application
Gouache can be applied with the sable brushes used for watercolors, with stiffer bristle brushes if applied more thickly, with a pen, or by airbrush.

3. Modifications for special applications and effects (“Tricks of the Trade”)

• Gloss may be adjusted by adding more gum binder.

• Evenness of tone can be increased by adding glycerine.

• If using gouache in an airbrush where it will be thinned with water, adherence to the substrate can be increased by adding more gum arabic [17].

• To create more texture, manufacturers suggest mixing gouache with Aquapasto medium or other acrylic texture gels, but these materials have not been tested for stability.

• A combination of 70/30 deionized water/acetone aids pigment dispersion for better paint blending, reduces wicking, and speeds drying. This mixture can also be used at 60/40.

• A mixture of 3/1 or 1/1 water/ethanol can be used with gouache to break surface tension, improving wetting. Oxgall or Photo-Flo (Kodak) can also be used for the same purpose.

• Gouache is sometimes used as the lower layer in a two-layer system of inpainting because, since it is opaque and therefore reflects light, it covers well even in thin layers. Therefore, one can more rapidly achieve an opaque underlayer than is possible with various synthetic resin-bound inpainting materials. This can be especially helpful when losses are large. However, when dry, gouache appears more even in tone than when saturated with a varnish or overlying glazes, so care should be taken to get this layer even before applying the overlying glazes. Evenness of tone can be increased by not adding too much water and by selecting those colors rated as most opaque (for example, Schmincke rates its pigments at four levels of opacity). Tones selected should be slightly lighter, cooler, and more intense than the original. Gouache has been described as being appropriate for Early Italian pictures because of the “clean, precise, clarity” of its color. It has been used as an underlayer with a thin layer of varnish applied after inpainting and a final surface glaze of Gamblin or Maimeri Ketonic Colors , where it is reported to be unchanged in tone after 20 years. In a series of Paintings Specialty Group List posts from Jan. 15–18, 2009, most conservators preferred Schmincke Horadam gouache to Winsor and Newton gouache due to greater opacity and less tendency to peel. Jim Bernstein suggests that the peeling in Winsor and Newton gouache may be due to their greater addition of humectants. Other posters reported good results using Holbein gouache. The Calligraphy series from Schmincke Horadam was suggested as good for inpainting modern pictures.

4. Advantages

• Gouache works especially well in inpainting early Italian Renaissance paintings, where it can imitate the tempera paint of the original works. After the gouache is laid down, its tone and gloss can be modified by overlying glazes in a synthetic resin or natural resin medium.

• It remains soluble and thus can easily be removed.

• Old gouache retouching remains in place during varnish removal, provided there is no isolating varnish layer beneath it. Therefore, inpainted areas may not need to be redone, or they may need simply to be adjusted with glazes.

5. Disadvantages

• Because gouache dries lighter than its saturated color, this needs to be taken into account when applying the overlying glaze. Correct color matching can be improved by rolling mineral spirits over the gouache layer to check for its color accuracy when wet up.

• If one doesn’t achieve the correct color in the gouache layer, it is difficult to modify it by painting over it with more gouache because one easily can pick up the already applied layer.

• Gouache is opaque and therefore is not suitable for all applications.

• It sometimes doesn’t adhere well to the underlying surface, causing the gouache to bead up. This problem can be solved by adding a few drops of a surfactant, such as oxgall or Photo-Flo, to your water.

• Gouache is not always compatible with an extremely absorbent fill since the gouache binder may be absorbed by the substrate, causing cracking.

• Not all pigments work well in gouache. For example, zinc white (Chinese white), the main watercolor white pigment, can turn gray in gouache medium if mixed with Prussian blue, and it does not photograph in its true value. This graying has been documented in practice by Carolyn Tomkiewicz Zinc white is also much less opaque than titanium white. Lithopone, an inferior zinc pigment used in student grades, has a history of darkening when exposed to strong light. Some conservators who have had difficulty finding titanium white gouache have mixed Utrecht watercolor titanium white with their gouache colors to achieve a more stable tint.

• The pigments brown madder, bistre, VanDyke brown, chrome yellow, and Hooker’s green are not lightfast in gouache, nor are the violet colors.

Aging Characteristics

1. Chemical/physical alterations

i. Lightfastness

Questions about the stability of gouache are actually questions about the stability of its pigments, since the gouache medium is not protective against degradation by light. Since some gouache colors are not lightfast, it is important to select colors that are rated as permanent. However, evaluating lightfastness is somewhat complex, since many companies have their own rating systems that are different from the current ASTM standard. The current best standard for permanence is the “ASTM D5724 Specification for Gouache Paints.” This is a voluntary standard. Some manufacturers state on their labels that their gouache conforms to ASTM standard D4236, which is the mandatory standard for labeling of chronic health hazards, and it is not a permanence rating. As of this writing, two gouache companies, DaVinci and Holbein, comply with the D5724 standard. This does not mean that other companies’ products are less permanent, but only that they don’t use the ASTM permanence standard as their yardstick.

For example, Schmincke Horadam states that all its colors meet the ASTM D5724 standard except the color madder lake deep (color #12354). They supply their own MSDS, their color chart rates colors for both permanence and opacity, and they feel their permanence ratings are more stringent than the ASTM standard. Winsor and Newton also provides a permanence rating and recommends using only AA- or Arated paints if permanence is important. In the face of so many different standards, a useful rule of thumb might be that the higher-quality gouache manufacturers are more concerned with permanence, and if a company produces permanence charts and other details of testing in their promotional literature, their pigments will be more stable than companies offering no information at all. Note also that some of the names of the gouache colors may not actually reflect the true pigment composition of that color (for example, “ultramarine blue” may not actually be made with the pigment ultramarine). Therefore, the permanence rating is a better way to judge stability than simply relying on the color’s name on the tube. Another source to consult for the stability of individual colors is The Wilcox Guide to the Best Watercolor Paints by Michael Wilcox.

ii. Pigment interactions

Zinc white has been found to become chalky and to discolor in gouache, so most of the makers of high-grade gouache offer a titanium-based white in addition to zinc white. The DaVinci Paint Company offers only titanium white, and M. Graham Company’s two whites, Chinese White and Titanium White, are both made with titanium only.

2. Shelf life
Gouache theoretically remains permanently usable in the tubes if well sealed and not exposed to the air. Paints will not change color, but after many years they may become hard in the tubes.

3. Removability
Gouache remains soluble in water even after drying.

4. Attraction of dirt and grime
Gouache has not been reported to attract dirt and grime.

Health and Safety

1. Storage
Gouache is stable under normal conditions. It should not be exposed to excessive heat for long periods of time. Winsor and Newton lists its gouache as pH 6- and its boiling point at above 100°C. Gouache may coagulate at freezing temperatures (M. Graham and Co. Material Safety Data Sheet).

2. Handling

No special equipment is required. There are no inhalation health risks under normal use. Ingestion may cause irritation to the gastrointestinal system. Avoid prolonged skin contact; wash with soap and water to remove.

Carol Christensen

Submitted January 2009

Plaka (Casein Paint)

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Principal Name

Casein tempera, casein emulsions, casein colour, PlakeⓇ, ShivaⓇ

Other Names

Milk paint, farmer paint, badigeon, casein lime paint, casein fresco, casein gesso

History of Use

1. Industrial
From ancient times, casein, a derivative of milk, has been one of the earliest paint binders and adhesives known. It is probable that casein was used in the cave paintings of southwest France and northeast Spain in 20,000 to 15,000 BCE. Cattle and goats were domesticated for milk, among other uses, in Turkey and other Near East sites from 10,000 to 6,600 BCE.

From Gettens and Stout we know that “it has served extensively as a binding medium for cold-water house paints and, to a limited extent, for pictorial painting, both as a binding medium and in the preparation of grounds. Craftsmen of ancient Egypt, Greece, Rome, and China are considered to have used casein”. Hermann Kühn reported in 1966 that he found proteins in samples of Hellenistic wall paintings from Bulgaria, indicating the presence of a casein and lime binder. In ancient Rome, we know from Pliny the Elder’s Historia Naturalis that “… the Romans were familiar with various binders which could be used on adry rendering, e.g., animal glue, gum, egg, honey and milk…” Ancient Hebrew texts mention the use of curd (casein) in house painting and decoration.

Casein or pot cheese was used as an adhesive by woodworkers in the ancient Middle East. Without doubt, it was a joining adhesive in the cabinet work of the Middle Ages. The preparation and use of casein were described as far back as the 12th century by Theophilus Presbyter. . Michelangelo is said to have used a combination of sour milk, oil, and pigments to produce highlight effects on walls. Lime casein was used in many well-preserved 18th-century ceiling paintings in upper Bavaria and Tyrolean peasant houses. They were painted either into still moist fresco plaster or into a lime wash. Many wall and ceiling paintings of that time are these so-called “casein frescoes”.

Commercial preparation of casein paints began around 1900 (CAMEO). Tempera painting, using either egg or casein as a binder, surfaced in the 1920s in the United States, where artists had adopted its use from British and German painters who already had a strong tradition of casein decorative painting from the previous century. Casein paint was imported from Germany to the United States as early as 1928. Ralph Mayer concurs, noting in his handbook that tubes of commercially prepared tempera were highly developed in Germany, where all types were made. According to the artist A. R. Katz, who rediscovered casein in 1927, the artist Ramon Shiva was already using casein in the United States and pioneered in originating a new line of colors that were soon to be sold in art stores everywhere. In 1933, Shiva began to produce “… a high grade commercial version [of casein glue and paint], using an emulsion composed of casein glue plus a very small amount of linseed oil…”. According to their website, the Pelikan company of Germany introduced their first line of Plaka casein colors to the market in 1934.

In the 1930s, Daniel Thompson’s The Practice of Tempera Painting and a translation of Max Doerner’s The Materials of the Artist were very influential to a generation of American artists exploring the rediscovery of medieval and Renaissance techniques of tempera and fresco painting. The revival of casein painting took hold roughly from 1930 through 1950. For many WPA projects executed from 1935 until 1943, artists used egg and casein tempera in studies for murals because these media were durable, permanent, fast drying, and resulted in a “look” that approximated fresco. Dispersions of synthetic polymer emulsions replaced casein as a paint medium in the early 1950s in the United States because they possessed most of the advantages and none of the drawbacks of casein.

2. Conservation
The casein paint used in conservation is sold under the trade name Plaka. It is commercially manufactured by the German company Pelikan. It is currently the only casein paint reported for use as an inpainting medium, for underpainting of fills, and as a toned fill material. Perhaps because of its long tradition as a paint binder and adhesive in cabinetmaking in Europe, Plaka casein colors are currently used more commonly by European painting conservators than by their North American counterparts.

Source

1. Physical
Commercially manufactured artists’ grade casein paint is sold in tubes or small jars ready to be diluted with water for application.

2. Original and manufacture
In general, we know from Gettens and Stout that the binder “casein is prepared from skimmed milk by heating it at 34.5° to 35°C and adding hydrochloric acid till the mixture reaches a pH of 4.8. It is then allowed to settle and, after separation from the supernatant liquid, is washed with hydrochloric acid, also with a pH of 4.8. Casein so prepared is technically pure, and is a snow white, slightly hygroscopic powder...” To make a casein paint, the casein powder is mixed with water and alkalis forming a colloidal solution to which the pigments are added. For best quality results, the alkalis of choice would be ammonium compounds such as ammonium carbonate. Commercial caseins are often prepared with potash or soda. In traditional paints used for wall paintings, the alkali’s source would have been slaked lime when the desired product was a coarser casein paint. Some commercial preparations, such as Shiva, add a small amount of linseed oil in their preparation, perhaps to enhance its flexibility and emulsifying properties.

3. Manufacturers and vendors
Plaka is produced in Germany by the company Pelikan and can be found through various suppliers of art materials in North America. The manufacturers of Shiva, Grumbacher, and Permanent Pigments have also been making casein colors, but their use as an inpainting medium by conservators has not been reported.

Chemical and Physical Properties

1. Chemical classification
The significant ingredient of Plaka colors is casein, which is an organic compound belonging to the class of proteins, grouped with one of the more complex subdivisions, the phosphoproteins. It consists of carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus. Like all proteins, it is amphoteric, i.e., it functions both as an acid and a base. It has, however, decided acid properties and exists in milk as calcium caseinate, a salt of calcium.

2. Chemical formula/structure
The definition of casein, according to Wikipedia, states:

Casein consists of a fairly high number of proline peptides which do not interact. There are no disulfide bridges. As a result, it has relatively little secondary structure or tertiary structure. Because of this, it cannot denature. It is relatively hydrophobic, making it poorly soluble in water. It is found in milk as a suspension of particles called casein micelles, which show some resemblance with surfactant-type micellae in a sense that the hydrophilic parts reside at the surface. The caseins in the micelles are held together by calcium ions and hydrophobic interactions.

3. Solubility
Casein paint, which is considered a tempera, is an aqueous paint system made by dispersing pigments in an emulsion. As an emulsion, tempera always contains a mixture of aqueous and non-aqueous binders. When initially working with wet casein paint, it is soluble in water. It remains partially soluble shortly after and is not waterproof until fully cured. However, in certain types of thinner applications, it may be removable with warm water.

4. Tg
At room temperature, the dried paint film is brittle and is not recommended for inpainting on stretched canvas or on other flexible supports.

Preparation and Formula

1. Typical application methods
Plaka is removed from the small jars in which it is sold using a microspatula or other suitable tool, and transferred onto a palette for mixing. Before application, it is recommended that the paint brush be loaded with water and the colors be mixed thoroughly and thinned to the desired consistency.

2. Additives
Although Plaka colors are available in a variety of hues, dry pigments can be added to widen the spectrum of colors as needed.

3. Storage/shelf life
It has been observed by conservators that 5- to 10-year-old Plaka colors whose water content has evaporated, leaving a thickened paste paint, can be thinned successfully with water, provided they are not completely hardened. For best results, jars should be stored with the caps screwed on tightly in closed plastic bags. Completely hardened paints cannot be reconstituted for use.

According to Gettens and Stout writing in 1942, it was generally difficult to keep casein in tubes without the paint hardening and crumbling (9). Glycerine may be added in some commercial preparations to keep the paint moist. However, this additive could make them more susceptible to mold growth. Sheila Ross, a Shiva employee, stated in an article in 1975 that the early tubes of Shiva casein paints had an uncertain shelf life caused by hardening or separation of the pigment and binder, but that by the1930s those problems had been resolved. Certain casein paints, such as those used by decorative wall and theater set painters, have a limited shelf life in larger quantities and can putrefy. This leads one to believe that Plaka may have preservatives or small amounts of linseed oil in it.

Handling Characteristics

1. Appearance
Plaka colors are opaque colors, water-soluble while wet, which behave very much like egg tempera or gouache colors. They have more body than either paint and enough for slight impasto techniques. However, thicker applications are not recommended since they will crack and may not dry properly. Casein paints are smooth and more workable than acrylics. As they have a very strong covering power, they maintain their opacity in thin applications. Similar to a gouache, they dry to a slightly lighter shade and darken considerably when varnished. In very dilute applications, they can appear as watercolors without the brilliance. They are completely matte when dried and can be buffed with a dry cotton swab to a dull sheen, making them very suitable for conservation of murals and fresco-like surfaces.

2. Application
Plaka colors are completely water-soluble when taken from the jar. However, they dry quickly on the palette and can sometimes be reconstituted when color mixing during the same inpainting session. They also dry quickly upon application to the fill surface. As a result, they are best suited for shorter strokes executed in thinner applications.

3. Modifications for special applications and effects (“Tricks of the Trade”)
Although casein is reported to be irreversible and therefore unacceptable as an inpainting medium, several conservators describe Plaka colors’ unique properties as useful for certain types of inpainting, underpainting, and texturing of fills. They are ideal for inpainting techniques using pointillist and short hatch-strokes as they dry very quickly. Some conservators have reported Plaka to be particularly helpful on fresco projects. During a recent treatment of a fresco in the United States, the Italian fresco conservator Giovanni Cabras suggested that some fresco conservators in his native country prefer using Plaka because its body and sheen upon drying are more aesthetically compatible to the surface of a fresco than any other inpainting medium. Cabras and his colleagues also believe that when used in dilute concentrations, it can be removed easily and is ideal for toning back pinpoint losses in frescoes by diluting it very thinly as a watercolor.

Also in this context for larger filled losses, one can carefully integrate the whiteness of the fill by slowly adding small, light-handed touches of a neutral beige color rather than color matching. This allows the original paint to be the protagonist of color so that the inpainted fill doesn’t become heavy. The technique is similar to working with watercolor: one would use the lightness of the non-original intonaco fills for the lighter colors. Only when there are darker areas to be inpainted would a little white be added to the palette for the needed opacity. Other American conservators feel that Plaka colors are difficult to color match when using mixtures containing white because of their color shift upon drying. However, compensation for this shift can be made when mixing the color on the palette.

Some conservators have reported the use of casein for underpainting and texturing fills followed by a more traditional, reversible inpainting palette. Since Plaka has some body and dries insoluble in water or solvents, it is useful for building up texture on a smooth fill, provided the fill material is removable, thereby isolating the Plaka in reversible adjacent layers.

London conservator Valentine Walsh reports that she has used Plaka as a fill material for small losses in copper panels since it remains in place when any excess is cleared with warm water or carved away with a scalpel. She notes that it can be applied very thinly and can be easily matched to any ground color. It should be applied very carefully, only in the loss and not over surrounding original paint layers since it may not be reversible.

Walsh has also used Plaka for retouching small losses on frames and other gilding. In this case, the conservator matched the bole color or general tonality of the gilding. Plaka comes in a variety of colors, including metallic colors, although no conservators reported their use.

Aging Characteristics

1. Chemical process
In casein paint, calcium and similar multivalent alkalis create cross-links, forming an insoluble product. Certain commercial formulations contain small amounts of linseed oil, which oxidizes and polymerizes, forming cross-links. This further contributes to the paint’s insolubility over time (for more details, see section III.B.2.a on drained oils as an inpainting medium).

2. Resultant chemical and/or physical alterations
Casein paint generally becomes a hard and brittle film upon aging and therefore is not recommended for use on flexible substrates such as stretched canvas. It is better suited for conservation of wall paintings and fragments thereof that have been mounted to rigid supports.

3. Impact on appearance, solubility, and removability
Because of the unpredictability on the issue of insolubility, it is generally recommended that inpainting with Plaka be limited to areas of fills. Theoretically, casein reacts as a weak acid; when fully cured, it is insoluble in water, alcohol, and other neutral organic solvents and is soluble in the carbonates and hydroxides of the alkali and alkaline earth metals and in ammonia. Although theoretically casein colors become waterproof within 24 hours of initial application, some conservators observe solubility using light moisture for much longer. Plaka colors used in very dilute concentrations can be easily removed. The addition of glycerine for flexibility in some commercial preparations keeps the paint moist, but destroys the insolubility of casein in water. Although casein paints are chemically miscible with resins and oils, it is not recommended because they can darken considerably and become even harder to remove.

4. Attraction and retention of dirt and grime
Casein paints are matte when dried and, depending on the atmosphere in which the paintings are housed, will retain dirt and grime more readily than traditional varnished inpainting materials. Surfaces of dried paint that have been buffed with a dry cotton swab producing a dull sheen will mitigate the ability for retention of atmospheric dirt.

5. Theoretical lifetime
In a good environment that is well-suited for most paintings collections (generally speaking, 68°-72°F +/- 2° and 45%-55% RH), casein inpainting should be able to withstand the aging process with no appreciable visual shift or loss of structural integrity.

Health and Safety

Casein can support mold growth if applied in thicker layers if glycerine is present in the formulation or if casein paints are applied in damp environments.

Health and Safety

There are no specific standards for disposal of the medium in Plaka, although certain colors may contain heavy metal-containing pigments requiring specific guidelines for their disposal.

Lisa Leto-Fulton

Submitted June 2008

Inks

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Principal Name

Higgins Waterproof; FW Waterproof Drawing Ink; Luma Brilliant Concentrated Watercolors; Winsor & Newton Ink; Pelikan Drawing Ink, Waterproof

History of Use

1. Industrial
Since antiquity.

2. Conservation
The author has used inks since 1985. It is not known how long they have been in use for inpainting.

Source

1. Physical
There are different sources, depending on color.

1. Manufacturers and vendors
Higgins: Sanford, Bellwood IL (Newell Company) FW: Steig Products Luma: Daler-Rowney, Jamesburg, NJ Winsor & Newton: London HA3 5RH England Pelikan: D-3000, Hanover 1, Germany

Preparation and Formulation

1. Typical application methods
As packaged by manufacturer.

2. Additives
As supplied by manufacturer.

3. Storage/shelf life
Depends on brand and storage methods. The tighter the seal after opening, the longer the inks remain liquid and viable for use.

Handling Characteristics

[Note: The inks are used as a base coat before subsequent retouching. Inks provide a good initial color for further inpainting because they penetrate the fill material without adding another distinct layer, and there are no discreet pigment particles to affect the texture of the retouching.]

1. Appearance
Straight from the bottle, the inks can be quite intense. This quality can be a benefit or a hindrance depending on the color to be matched. Also, the inks can appear shiny depending on the manufacturer and the inclusion of shellac. The sheen disappears with the application of the subsequent retouching layer.

2. Application
First the loss is filled with white gesso and textured to match the surrounding area. The inks then are applied in a manner similar to watercolor painting, i.e., the white ground may be used as a factor in the color mixture. Inks may be mixed together in simple, limited combinations to achieve colors other than those directly obtainable from the bottles. Too much mixing results in a muddy color.

3. Modifications for special applications and effects (“Tricks of the Trade”)
For a light color, the ink may be diluted with water. For dark colors, the ink may be used directly from the bottle, followed by a thin glaze or scumble to achieve the final match. In general, if the desired color cannot be matched with the ink, it is better to keep the inks a little lighter and cooler.

Preparatory ink applications are especially useful for inpainting surfaces with little to no impasto, such as 14th- to 16th-century panels where the paint layer is extremely thin but the color is intense. This method works especially well with blacks when India ink is followed with a warm glaze.

Inks used as a base coat can speed up the total inpainting process. As a preparatory step, their application suggests the final appearance of the painting while still leaving room for modification. The ink layer can be transparent or opaque, depending on the individual painting and desired effect. For example, if the ground or ground color is part of the final effect, the inks may be applied transparently, as in a watercolor. For a richer, more intense color, an opaque application may be preferable. Typically, inks are applied prior to the application of the isolating varnish, for varnish may block the penetration of the ink into the fill. Varnish may be applied around the edges of the loss/fill prior to ink application as a precaution. The author has never had a problem with ink stains at the edges of the loss.

Inks also may be used late in the inpainting process, such as in the reconstruction of rigging in a ship or to reproduce fine cracks.

Typically, a brush is used for the application of inks. Brush size depends on the size of the loss and what is meant to be reconstructed.

Aging Characteristics

1. Impact on appearance, solubility, and removability
Inks can be easily removed with moisture and the fill material.

2. Attraction and retention of dirt and grime
The inks are an underlayer and not susceptible to dirt and grime.

3. Theoretical lifetime
Changes have not been detected through glazes and scumbles in the subsequent retouching layer. Lightfastness or changing of color has not been detected in 25 years.

Health and Safety

Inks are very safe to use.

Eric Gordon

Submitted April 2004

Oil

Drained Oil

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Principal Name

Drained oil, extracted oil, leeched oil; variant: oil-resin color

History of Use

1. Artistic
In the 19th century, some artists’ manuals advised placing oil paint onto blotter paper or another absorbent surface as a method to draw out the excess oil often encountered in commercially produced paints. This procedure is written about at least as early as 1858 in A. Ducrot’s La peinture à l’huile et au pastel apprises sans maître, in which unsized paper or wood is recommended for this purpose. In 1881, in A Course of Lessons in Landscape Painting in Oils, Alfred Grace remarked that too much oil would lead to “the dead, muddy, leathery look in your painting which is so disagreeable” and went on to propose extracting the excess oil on blotting paper. Philip Gilbert Hamerton, in his 1882 book titled The Graphic Arts, noted that a fellow artist “…like Sir Frederic Leighton…objects to oily colours, and extracts superfluous oil by squeezing the pigment upon blotting-paper” The chemist Sir Arthur H. Church in The Chemistry of Paints and Painting also recommended the practice and further stated that a clean block of Plaster of Paris was the best surface for drawing excess oil out of the paint. In 1891, the academic painter Jehan George Vibert, remarking on the common belief that too much oil led to darkening, wrote that “many artists, convinced of this excess, have adopted the custom of leaving their colours some minutes on blotting paper before using them”.

In addition to minimizing certain perceived defects, the technique of oil extraction was also used to modify the paint’s handling properties and appearance. By the late 19th century, particularly with the advent of Impressionism, many artists used this method to obtain paint that was leaner, more easily impasted, and dried faster. When asked why he put his paints onto blotting paper, Claude Monet responded that he believed there was too much oil in commercial paints and that he was interested in achieving a more matte surface. Edgar Degas was known to draw out excess oil before diluting with turpentine to produce matte washes of paint in a technique called peinture à l’essence ; Fletcher and DeSantis 1989, 257). Pierre Puvis de Chevanne as well was observed by a former student to drain his oils on blotter paper to create his fresco-like surfaces.

2. Conservation
When using oil paint for retouching, extracting excess medium is a logical attempt to address the disadvantages of oil paint while still retaining the advantages. In the late 19th century, Giovanni Secco-Suardo remarked on the practice in his manual Il Restauratore dei Dipinti that some restorers extracted oil on absorbent paper and diluted the paints with turpentine as a way to prevent the darkening and deadening of the colors after drying. Although this practice helped to some degree, he noted that the discoloration would still occur over time. For this reason, he said that the majority of restorers used pigments mixed with turpentine and tempered with varnish.

In the 20th century, drained oils have been included in overviews of restoration materials techniques, such as those of Emile-Mȃle and Nicolaus , often with the caveat that they are known to discolor over time. Although drained oils have largely fallen out of use in favor of more stable alternatives, their facile handling properties and rich saturation have ensured their continued usage by some conservators today, both in America and abroad.

Source

1. Physical
Commercially produced artists’ grade oil paint sold in tubes.

2. Origins and Manufacture
The colors are typically high-quality paints consisting of finely divided pigments bound with linseed and/or safflower oils. Safflower oil⁹ tends to dry more slowly but yellows less than linseed oil and is frequently the medium of lighter colors and white.

3. Manufacturers and vendors
Winsor & Newton and Schmincke are two companies with a reputation for a high degree of purity and consistency of materials.

Chemical and Physical Properties

1. Chemical classification
Drying oils, such as linseed and safflower oil, consist primarily of triglycerides, which are the esters of glycerol with fatty acids. A high proportion of fatty acids in the triglycerides must be unsaturated to provide sufficient reactivity to allow for the oxidation and polymerization processes required for drying. The triglycerides in drying oils typically consist of polyunsaturated linoleic and linolenic acids, in combination with other species including oleic, palmitic, and stearic acids.

2. Chemical formula/structure

Figure 3 Chemical structure for Oil, Courtesy of Elise Effman-Clifford

R, R’, R”= fatty acid chains

Fatty acids found in linseed oil:

Linoleic. HOOC (CH₂)₇ CH=CHCH₂CH=CH(CH₂)₄CH₃

Linolenic HOOC (CH₂)₇(CH=CHCH₂)₃CH₃

Oleic HOOC (CH₂)₇CH=CH(CH₂)₇CH₃

Palmitic HOOC (CH₂)₁₄CH₃

Stearic HOOC (CH₂)₁₆CH₃

3. Solubility
The solubility of drying oil decreases over time as the cross-linkage of triglyceride molecules occurs. Solubility in alcohols and acetone is increased by the addition of dammar or mastic varnish to the medium.

Preparation and Formulation

1. Typical preparation methods
Oil paint is squeezed out from the tube onto blotter or filter paper and allowed to sit for several days to pull out excess oil. Even after a few hours, a ring of oil will be noticeable on the paper. Turpentine and xylene are both possible diluents.

2. Additives
Natural or synthetic resin varnishes are typically added to increase the gloss and solubility.

3. Storage/shelf life
Oil paints will dry out in their tubes over time. Once squeezed onto a blotter palette, a skin will form after several days. This can be pierced to access fresh paint.

Handling Characteristics

1. Appearance
Saturated colors and deep blacks are possible due to the fine dispersion of the pigments in commercial artists’ oil paints and the refractive index of the medium. The fine particle size also contributes to a high degree of transparency that is particularly conducive to glazing. When used in the final stage in a layered retouching system, drained oils can convincingly imitate the patina of an aged oil paint. Drained oils are not a stable inpainting material. When used thickly and opaquely or in light areas, a noticeable color shift will occur over time.

2. Application
Due to their transparency and saturation, drained oils are most commonly used as a final thin glaze over another lighter and more opaque underlayer. Usually the underpaint is water-based like gouache or tempera, although other retouching media, such as pigments in poly (vinyl acetate) or Paraloid. B-72, could be used as well. Drained oils are known for being easy to work with because they dry more slowly and have more fluid handling properties than water-based and synthetic retouching materials. Some practitioners use the medium directly, without a base layer.

Aging Characteristics

1. Chemical process
The initial oxidation and polymerization that converts the liquid paint into a solid film is a complex process resulting from a series of free radical chain reactions. In addition to reactions that result in cross-linking of triglyceride molecules, other oxidation and hydrolysis reactions occur, which result in low-molecular weight degradation products.

2. Resultant chemical and/or physical alterations
Drying oils yellow over time due to the accumulation of chromophores as part of the aging process. This yellowing contributes to the color shift often observed in oil paints. Because the extraction of oil on blotter paper only removes excess medium, drained oils are still oil paints and will polymerize and yellow.

3. Impact on appearance, solubility, and removability
Drained oils are reversible when isolated from the painting surface by varnish or another retouching medium. Solubility is further increased when a resin varnish is added to the paint. Discoloration, however, is a significant issue in considering the use of drained oils. Essentially, there are two main views about their use in conservation. Some conservators believe that the inherent instability of the medium and the availability of more stable alternatives are reasons enough to preclude their use in any restoration. Numerous instances can be cited where the injudicious application of oil retouching has resulted in noticeable alterations.

Other conservators note that when drained oils are used sparingly and mixed with varnish for use as thin glazes in dark and/or richly saturate areas, the resulting discoloration observed is comparable to a natural resin varnish. In conversations with some museum conservators who have paintings in their collections that have been restored using this technique in moderation, many note that there actually has been little if any noticeable alteration after twenty years.

4. Attraction and retention of dirt and grime
There is no evidence that drained oils preferentially attract dirt or hold grime.

5. Theoretical lifetime
When used sparingly as a glaze over a stable underpaint, the retouching should last as long as the natural resin varnish.

Health and Safety

Refer to the Paintings Specialty Group’s Painting Conservation Catalog, Volume 1: Varnishes and Surface Coatings (1998) for added resin [see https://conservationwiki.com/index.php Website].

There are no specific health and safety concerns with linseed or safflower oil. The general concerns about hazardous pigments and solvents apply.

Disposal

There are no specific regulations on disposal.

Elise Effmann-Clifford

Submitted February 2010

Solvent-Based Resins

Low Molecular Weight (LMW) Resins

Maimeri Restauro Varnish Colours

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1. Principal name
Maimeri Restauro Varnish Colours

2. Other names
Maimeri, Varnish colors

3. History of use

i. Industrial

Maimeri Restauro Varnish Colours were developed expressly for use by conservators and restorers. (The author is not aware of any documented use by artists, although there is some discussion of experimentation with the Varnish Colours on various artist message boards.)

ii. Conservation

Maimeri Restauro Varnish Colours were introduced in c. 1950 by the Maimeri Gruppo in Italy (Maimeri, personal communication, 2008). Developed exclusively as conservation/restoration paints, they were likely developed as a commercial (ready-made) alternative for drained oil paints and “hand-mixed” resin/varnish colors, which at the time were the most commonly used media for retouching. The use of the Varnish Colours spread quickly from Italy to conservators and museums in other countries. The Instituto Centrale del Restauro appears to have been key in promulgating the use of the Maimeri Varnish Colours.

4. Source

i. Physical

Maimeri Restauro Varnish Colours are currently available as 20ml tubes in a range of 33 colors.

ii. Origins and manufacture

Maimeri Restauro Varnish Colors are a proprietary product manufactured by Maimeri Gruppo of Milano, Italy. Maimeri was founded in 1923 by Italian Impressionist painter Gianni Maimeri. The Restauro line was developed in c. 1950 specifically for the restoration/conservation profession.

iii. Manufacturers and vendors

Maimeri Restauro Varnish Colors are manufactured exclusively by the Maimeri Gruppo of Milano, Italy. They were officially introduced in the United States in 1981 by the Charvoz-Carsen Corporation (no longer in business) in partnership with Maimeri Gruppo. However, numerous museums and conservators had already been using the Varnish Colours for some time, and several U.S. art supply stores already carried them. They are currently available from a number of conservation suppliers and art stores.

5. Chemical and physical properties

i. Chemical classification

Proprietary mixture containing primarily a natural resin (mastic), pigment, and solvent.

ii. Chemical formula/structure

According to Maimeri Gruppo, the Varnish Colors are a mixture of “pure, authentic, lightfast pigments mixed with mastic resin and refined hydrocarbon solvents” with the mastic coming “exclusively from ” . Analyses conducted at the Canadian Conservation Institute (CCI) in 1989 and at the National Gallery of Art, Washington, D.C. in 2000 both confirm the presence of gum mastic. Mastic is a triterpenoid resin derived from the sap of a tree, Pistacia Lentiscus; it has a varied and complex composition based on a structure composed of six isoprene units (see the Paintings Specialty Group’s Painting Conservation Catalog, Volume 1: Varnishes and Surface Coatings). The 1989 analysis conducted at CCI revealed that the solvent was likely a-pinene (a purer form of oil of turpentine). However, a 2000 Safety Data Sheet (the European equivalent of MSDS) states that the solvent mixture contains Petroleum Naphtha (CAS # 64742-82-1, a hydrosulfurized heavy naphtha aliphatic solvent) and Solvesso 100. (CAS # 64742-95- 6, a 97 percent aromatic solvent composed primarily of C9-10 dialkyl and trialkyl-benzenes). Based on these findings, it seems likely that the solvent mixture has changed over time.

It is important to note that several Maimeri colors are actually composed of a mixture of pigments, i.e., Naples Yellow consists of a mixture of zinc oxide, an arylide yellow, and synthetic iron oxide; Titanium White is actually a mixture of titanium dioxide and zinc oxide. Currently the label on each tube lists both the pigment name and the Color Index Name (2 letters and several numbers) of all individual pigments contained within that color. (Older tubes may not have this information; it is provided on the Maimeri website.) In addition, synthetic pigments have replaced some of the pigments initially used, i.e., Madder Lake Deep—a rose madder—has been replaced by Permanent Madder Deep—an anthraquinone lake. (Note: The CI name, PR83, for the anthraquinone lake designates a natural anthraquinone, which is only marginally more lightfast than madder). Several of the pigments used have mixed or poor lightfast ratings. These include Permanent Carmine (ASTM IV); Permanent Madder Deep (ASTM IV for one pigment); Green Lake (WG V for one pigment); Brown Madder (ASTM IV for one pigment); and Vandyke Brown (ASTM V for one pigment) (ASTM rating as given in Wilcox 2000).

iii. Solubility

The Varnish Colors are initially soluble in a range of solvents including low aromatic mineral spirits, xylenes, toluene, isopropanol, 1-methoxy 2-propanol (e.g., ArcosolvⓇ PM), and various mixtures of solvents. (A small degree of polarity or small fraction of aromatics is needed for full solubility.)

iv. Tg

While the Tg of these proprietary paints has not been provided by the manufacturer, the Tg of mastic is –34.7˚C (see volume I of the PSG catalog, Varnishes and Surface Coatings). The Tg of Maimeri Restauro Varnish Colors may be expected to be similar.

6. Preparation and formulation

i. Typical application methods

Maimeri may be used alone or, as is more common, applied over an initial layer of inpainting (often opaque and lighter/cooler), such as watercolor, tempera, or gouache. Current practice at the Istituto Centrale per il Restauro (ICR) is to first tone the fill with watercolors, apply a spray varnish, and then do final toning with the Varnish Colours. Several of the colors are quite transparent. Each tube carries a symbol on its label designating the transparency of that color. The fine grind, good dispersion, and transparency of the Varnish Colours make them particularly well-suited for glazing and building up layers of glaze.

ii. Additives

The 1989 analysis at CCI found the presence of various stabilizers: aluminum soaps, silica, clay, and wax. A 2003 study also found the addition of calcium carbonate, an extender, in some of the Colors.

iii. Storage/shelf life

Tubes of paint should be stored in a cool, dry area. Because the colors are in aluminum tubes, there is no specific need to store them in the dark. Shelf life will depend on how often the tubes are opened and how tightly they are resealed.

7. Handling characteristics

i. Appearance

Upon drying, the colors have a semi-gloss appearance. One significant advantage of the Varnish Colors is that there is no color change from wet to dry. The gloss of individual colors varies such that there is no consistent level of gloss within the set of colors. The Varnish Colours can be valuable when trying to match dark, transparent aged oil films.

ii. Application

The colors are generally applied using a small inpainting brush in small dots or strokes. Faster evaporating solvents will produce a slightly more matte appearance. Adding additional mastic resin will produce more glossy colors.

iii. Modifications for special applications and effects (“Tricks of the Trade”)

The colors can be mixed with additional resin to create very transparent glazes.

8. Aging characteristics

i. Chemical process

Two considerations determine the aging characteristics of Maimeri Restauro Varnish Colours: the aging of the mastic resin and the long-term stability of the pigments. The aging of mastic resin is a complex autoxidation process. Basically, it proceeds quickly via radical chain reactions that proceed both in light and dark environments, resulting in yellowing and a loss of transparency. . Feller et al. noted that mastic dissolved in turpentine and spread into a film begins to oxidize rapidly. Pigments age via photodegradation processes most often resulting in fading and/or in some cases darkening or chromatic changes.

ii. Resultant chemical and/or physical alterations

(see below)

iii. Impact on appearance, solubility, and removability

Only a few studies have looked specifically at the long-term aging of Maimeri Restauro Varnish Colours. All found that there are significant changes to the appearance, solubility, and removability of the Varnish Colours—in some cases after only 405 hours of accelerated aging, which corresponds to only a few years under typical museum lighting conditions.

Most of the Varnish Colours tested exhibited color changes during artificial aging primarily due to degradation of the resin. Ultramarine and ivory black underwent significant color changes: the ultramarine increased in both lightness and chroma, with a shift from reddish blue to a greenish blue; ivory black decreased in lightness. With more prolonged aging, many other colors also showed changes: the yellow ochre increased in lightness and decreased in chroma, with a slight shift from a reddish yellow towards a more greenish yellow; the alizarin decreased in lightness. Viridian showed a decrease in lightness and an increase in chroma. Titanium white shifted toward the yellow. Only the cadmium yellow demonstrated some color stability. Cerulean blue, ultramarine, yellow ochre, and green earth were found to be only moderately light-fast, while the alizarin reds (Permanent Carmine and Permanent Madder Deep) border on low stability.

One of the primary concerns in using Maimeri varnish colours is the yellowing of the colors over time, due to aging of the mastic resin. A number of conservators report using only the darker colors, where discoloration is thought to be less problematic. However, as shown in testing by de la Rie et al., darker colors may lighten. Artificial aging in both light and dark conditions produced chromatic alterations in the Varnish Colours tested. The lighter Varnish Colours, in particular the white, showed marked yellowing. Those paints that contain high binder absorption pigments, such as black, browns, and other earth pigments, showed a more marked tendency to change.

After artificial aging, thin films of the Varnish Colours became extremely matte, and many had fine cracks and were flaking. Isolating the Varnish Colours with an acrylic varnish helps to stabilize changes in gloss. The inclusion of zinc oxide in the Titanium White has an unfavorable effect on aging, resulting in degradation and interlayer chalking, visible as whitening of retouching layers containing some white.

Maimeri Restauro Colours rapidly become insoluble in non-polar solvents. Interestingly, this effect was diminished in ivory black. In addition, the Varnish Colours were the only retouching paints tested that also changed solubility in the dark. Varnishing with an acrylic was found to positively impact the solvent removability of the Varnish Colours.

iv. Attraction and retention of dirt and grime

Similar to mastic.

v. Theoretical lifetime

Similar to that of natural resin varnishes, the degree and onset of perceptible yellowing and degradation will vary depending on environmental conditions, etc. (not a Feller Class A material).

9. Health and safety
Mastic resin presents no acute health hazards. However, the solvents used both in manufacture of the paints and during inpainting may pose health risks. Use with adequate ventilation and avoid contact with skin and eyes. Keep away from heat and flame.

10. Disposal
Dispose of in accordance with local regulations.

Maimeri Restauro Ketonic Resin Colours

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1. Principal name
Maimeri Restauro Ketonic Resin Colours

2. Other names
Maimeri Ketone Colors

3. History of use

i. Industrial

Not applicable. Maimeri Restauro Ketonic Resin Colours were developed expressly for use by conservators and restorers.

ii. Conservation

Maimeri Restauro Ketonic Resin Colours were introduced in c. 1998 by the Maimeri Gruppo in Italy (Maimeri, personal communication, 2008). According to Maimeri, this new line of colors, developed exclusively as conservation/restoration paints, was introduced in response to “recent demands of scientific research into the conservation of works of art” for use with modern synthetic varnishes [18]. Some have suggested that they may have been developed partially in response to the discontinuation of the Lefranc & Bourgeois/ Charbonnel colors (Hamm, personal communication, 2008).

4. Source

i. Physical

Maimeri Restauro Ketonic Resin Colours are available as 40ml tubes in a range of 20 colors.

ii. Origins and manufacture

Maimeri Restauro Ketonic Resin Colours are a proprietary product manufactured by Maimeri Gruppo of Milano, Italy. Maimeri was founded in 1923 by Italian Impressionist painter Gianni Maimeri. The Restauro Ketonic Colours line was developed in c.1998 specifically for the restoration/conservation profession.

iii. Manufacturers and vendors

Maimeri Restauro Ketonic Resin Colours are manufactured exclusively by the Maimeri Gruppo of Milano, Italy. They are currently available from a number of conservation suppliers and art supply stores.

5. Chemical and physical properties

i. Chemical classification

A proprietary mixture containing primarily a ketone resin (polycyclohexanone), pigment, and solvent.

ii. Chemical formula/structure

According to Maimeri Gruppo, the Varnish Colours are a mixture of “lightfast tested pigments with ketonic resin and selected hydrocarbon solvents” [19]. Maimeri states that the resin used is not a Laropal ketone (Maimeri, personal communication, 2008). Analysis conducted at the Museum of Fine Arts, Boston, in 2008 confirme the resin to be a polycyclohexanone with additional absorption bands that probably correspond to plasticizers and/or other additives. According to Maimeri’s head chemist, the Ketonic Resin Colours are made with a Cyclohexanone condensation product (Reifsnyder, personal communication, 2008). The 2003 Safety Data Sheet (the European equivalent of MSDS) states that the solvent mixture contains Naphtha Petroleum (CAS # 64742-82-1, a white spirit) and 1,2,4 Trimethylbenzene (CAS # 95-63-6, an aromatic isolated from the C9 hydrocarbon fraction).

As with the Varnish Colours, each tube’s label gives both the pigment name and Color Index number (two letters and several numbers) of all the pigments the color contains. (This information is also available on the Maimeri website) Several colors contain a mix of pigments, i.e., Payne’s Grey is composed of bone black and ultramarine. Also, as with the Varnish Colours, Titanium White contains a mixture of titanium dioxide and zinc oxide.

iii. Solubility

The Ketonic Colours are initially soluble in a wide range of solvents including petroleum benzine, white spirits, xylenes, isopropanol, 1-methoxy 2 propanol, and mixtures of solvents. They will become slightly less soluble over time in non-polar solvents. Maimeri states that the Ketonic and Varnish colors can be mixed and thinned using the same solvents.

iv. Tg

While the precise Tg of these proprietary paints is not provided by the manufacturer, the Tg of Laropal K80 (a polycyclohexanone) has been given as 42˚C. The Tg of Maimeri Restauro Ketonic Colours may be expected to be similar.

6. Preparation and formulation

i. Typical application methods

Maimeri is usually used alone, particularly on modern/contemporary and unvarnished works. However, it may be used in combination with an initial underlying layer of inpainting, such as watercolor, gouache, etc. Most of the colors have good opacity.

ii. Additives

No additives are substantiated, although the brittle nature of the resin suggests that plasticizers may have been added to counteract brittleness. Preliminary analysis found absorption bands that probably correspond to plasticizers or other types of additives.

iii. Storage/shelf life

Tubes of paint should be stored in a cool, dry area. Because the colors are in aluminum tubes, there is no specific need to store them in the dark. Shelf life will depend on how often the tubes are opened and how tightly they are resealed.

7. Handling characteristics

i. Appearance

Upon drying, the colors have a matte appearance. There is little color change from wet to dry.

ii. Application

The Ketonic Resin Colours are generally applied using a small inpainting brush in small dots or strokes. Faster evaporating solvents will produce a more matte appearance. Adding additional resin will increase gloss and produce more transparent colors.

iii. Modifications for special applications and effects (“Tricks of the Trade”)

The Ketonic Colours can be mixed with Maimeri Varnish Colours. They can also be used in conjunction with Gamblin Conservation Colors.

8. Aging characteristics

i. Chemical process

The chief path of degradation of polycyclohexanone resin is photochemically initiated autoxidation. There is no induction period, i.e., aging starts immediately.

ii. Resultant chemical and/or physical alterations

(see below)

iii. Impact on appearance, solubility, and removability

Very few aging studies have looked at the Maimeri Ketonic Colours. One study did find chromatic alteration of the Ultramarine Blue Ketonic Colour in dark aging and chromatic alteration of the Titanium White and Ultramarine Blue colors in light aging. In addition, changes in solubility are observed for the Ketonic Colours tested. Ketone resin films are hard and brittle. Ketone resins yellow less quickly than natural resins. Although they are initially more stable than natural resin films, autoxidation results in a rapid change in solubility, resulting in the need for more polar solvent mixtures for removal. Ketone resins are prone to yellowing in the absence of light, have a tendency to bloom and/or haze, and develop matte areas due to microscopic wrinkling.

iv. Attraction and retention of dirt and grime

Ketonic Colours are not excessively prone to attract dirt or grime.

v. Theoretical lifetime

Similar to that of a polycyclohexanone varnish (not a Feller Class A material).

9. Health and safety
Ketone resin presents minimal health hazards; however, contact with skin and eyes may cause irritation. The solvents used in the manufacture of the paints and during inpainting may pose health risks; use with adequate ventilation and avoid contact with skin and eyes. Keep away from heat and flame.

10. Disposal
Dispose of in accordance with local regulations.

Charlotte Seifen Ameringer

Submitted October 2008

Robert Gamblin Conservation Colors

1. Development and formulation
Robert Gamblin Conservation Colors are a commercially prepared palette of 44 pigments ground in a urea-aldehyde resin. During the 1990s, a collaboration among conservation scientists, conservators, and a commercial artists’ materials manufacturer produced an inpainting material that was designed to exhibit photochemical stability, lightfastness, and reversibility. It would also have working properties suitable for use with a wide array of painting styles and techniques. In addition, the low molecular weight resin would require mild solvents, making the paints safe to use.

Development of the product was detailed in a paper written by Mark Leonard, Jill Whitten, Robert Gamblin, and E. Ren. de la Rie delivered at the IIC conference in Melbourne. The collaborative team determined to develop an inpainting material that exploited the superior pigment wetting qualities of low molecular weight resins and the consistent pigment dispersion produced by industrial milling. The absence of a commercially available inpainting product that incorporated recent resin research prompted inquiries in search of a specialized paint manufacturer. By 1994, Gamblin Artists Colors Co. had agreed to produce a new inpainting material that would utilize a new low molecular weight (LMW) resin and commercially prepared pigments.

Data generated at the National Gallery of Art in Washington D.C. suggested that aldehyde resins manufactured by BASF showed good working qualities and exhibited photochemical stability. The aldehyde LMW resins exhibited more desirable paint medium qualities than other hydrocarbon LMW resins (e.g., ArkonⓇ P-90, RegalrezⓇ 1094) that were already being used for varnishes because their slight polarity permitted better pigment wetting. The resins’ high refractive index would produce good color saturation. An aldehyde resin, LaropalⓇ A-81, was identified as a readily available suitable resin. Twenty colors, selected for trial using results from a survey of conservators’ inpainting practices, were manufactured by Gamblin and distributed to conservators for use and evaluation.

Gamblin Artists Colors Co. began supplying a palette of 36 colors using Laropal A-81 binder and three-roll milling in May 2000. In July 2009, 10 new colors were introduced, bringing the palette up to 44 colors. (Two new colors were substitutions: Manganese Blue replaced the original Manganese Blue Hue, and Transparent Earth Orange replaced the original Mars Yellow. In addition, the original Transparent Mars Red was renamed Transparent Earth Brown.) In 2010, Gamblin acquired an electric muller that permits cost-effective production of paint in very small quantities. Specialized, rare, and hazardous colors (e.g., lead white, vermilion, and azurite) can be mixed into the Laropal A-81 resin to make custom inpainting colors. About 25–50g of conservator-supplied, powdered dry pigment is needed to manufacture a single jar. Robert Gamblin Conservation Colors are dissolved in a petroleum distillate mixture and are supplied in 15 ml jars. The medium for the colors, Galdehyde Resin Solution, is Laropal A-81 resin in petroleum distillate solution and is supplied in 4 fluid ounce bottles.

All pigments “are rated lightfastness I (excellent lightfastness)”. , with light-stable modern substitutes used for fugitive colors such as Indian Yellow, Alizarin Crimson, and Brown Madder. Gamblin’s Color Chart lists the Color Index name for each pigment. No additives are present except in modern organic pigments that contain “alumina hydrate to properly adjust tinting strength for better working properties&rdquo. [20]

The Gamblin Conservation Colors performed well in aging tests. They retained their original film gloss, except for titanium white, which became more matte. Aged paint films appeared as “smooth uniform surfaces with no signs of cracking or flaking”.

Aging tests carried out on a small test palette of seven colors milled with Laropal A-81 medium without the addition of a hindered amine light stabilizer (HALS) found that the colors’ solvent removability performance was comparable to the behavior of other synthetic resin inpainting media (e.g., Paraloid B-72, LeFranc & Bourgeois “Charbonnel Restoration Colours,” Bocour “Magna” and Golden “Polyvinyl Acetate Conservation Paint”. Additional tests on a preliminary light-stabilized palette showed that the color quality in some (e.g., Indian yellow, cobalt blue, and ultramarine blue) was substantially light stabilized when HALS inhibitor (Tinuvin 292, Ciba 1%) was added whereas other colors (yellow ochre, burnt umber, raw umber, raw sienna, permanent alizarin, and Indian red) showed only slight improvement. Other colors (chrome oxide green, viridian, titanium white, ivory black, burnt sienna, cadmium yellow light and medium, and cadmium red light and medium) showed no change. Likewise, the HALS (Tinuvin 292, Ciba 1%) additive improved solvent removability of some paint film colors (cadmium yellow light) but had no effect on others (titanium white and ultramarine blue). These findings led investigators to conclude that “Laropal A-81 paints appear stable enough to be used without the addition of a stabilizer such as Tinuvin 292”. The study further noted that the accelerated aging tests had been carried out in an environment that simulated daylight through window glass without ultraviolet filters. The paints could be expected to perform better in circumstances that included ultraviolet filtration.

2. Handling characteristics
i. Appearance
Robert Gamblin Conservation Colors have “handling and optical properties comparable to those of natural resin paints and are particularly suitable for use in glazes and where relatively high colour saturation is required”. The desire in formulating these products was to “enhance working properties while maintaining the permanence of the materials”.

The paints, supplied in 15 ml jars, are intentionally lean and dry matte. Most conservators who initially tested the colors responded positively to survey questions and found them easy to learn to use. The paints were noted as having “good covering power, versatility in the achievement of a variety of effects, little change in colour upon drying, usefulness for both glazing and scumbling and ease in editing with a silk cloth”. The few negative responses appeared to emanate from professionals who had mastered inpainting with conservatormade retouching materials.

In practice, this author has found that Gamblin Colors can become glossy when additional unaltered Galdehyde Resin Solution is used. The glossy inpainting can also have some perceived thickness where the retouching appears too high. This can be remedied by limiting the quantity of or diluting the supplied Galdehyde Resin Solution. Alternately, custom-made solution made with a few beads of Laropal A-81 in isopropanol can be used as added medium (Whitten, personal communication, November 26, 2008).

The palette includes a number of transparent and semi-transparent colors. Four transparent earth colors—Transparent Earth Brown, Transparent Earth Orange, Transparent Earth Red, and Transparent Earth Yellow—and Greenish Umber are especially useful for inpainting traditional oil paintings. Rich glazes are readily produced using these colors. Lamp black, so often useful to create saturated dark colors, was added in 2009.

Jim Bernstein likes to lay out the colors as shown in the following table.:

Gamblin Conservation Color Palette in Aldehyde Resin Laropal A-81 (BASFⓇ) (James Bernstein 2007)

Titanium White	Titanium White	Indian Yellow	Hansa Yellow Medium	Cadmium Yellow Light	Cadmium Yellow Medium	Cadmium Orange	Cadmium Red Medium-Light	Cadmium Red Medium	Quinacridone Red	Alizarin Permanent
Extender White (Chalk)		Chrome Titanate Orange					Yellow Ochre	Raw Sienna	Venetian Red	Dioxazine Purple
Manganese Blue Hue (Pthalo)	Chromium Oxide Green								Indian Red	Cobalt Violet
Cobalt Blue	Cobalt Green								Transparent Earth Yellow	Transparent Earth Orange
Prussian Blue	Viridian Green								Brown Madder Alizarin Permanent	Transparent Earth Red
Pthalo Blue	Pthalo Green								Burnt Sienna	Transparent Brown (Charbonnel) Lefranc-Bourgeois
Ultramarine Blue									Burnt Umber	Raw Umber
									Ivory (Bone) Black	Spinel Black

ii. Application
The use of Gamblin colors for a variety of inpainting projects is described by Jill Dunkerton in her article titled “Retouching with Gamblin Conservation Colours” in Mixing and Matching: Approaches to Retouching Paintings. As explained in the clear text and shown in the illuminating images, the colors have proved useful for inpainting both tempera and oil paintings on panel and on canvas. The colors’ fine quality permits their use for inpainting while employing binocular magnification. Specific pigment mixtures that Dunkerton finds especially useful are included in the article. Dunkerton practices strict “palette hygiene”; she maintains a separate palette exclusively for “translucent glazing” colors.

Robert Gamblin Conservation Colors can be used straight from the jar as supplied to produce a smooth matte surface. In practice, the paints used straight from the jar are gummy and difficult to handle (Whitten, personal conversation, November 26, 2008). More commonly, conservators remove the paints from the jar and allow them to dry out before re-dissolving them for use.

The pigment particle size is consistent, resulting in even color application with a high degree of saturation. The colors shift slightly on drying but change almost imperceptibly when used with additional medium or varnish.

Diluents: When the test panels were sent for evaluation in 1997, conservators were habitually using more polar and aromatic solvents than needed. Laropal A-81 requires a hydrocarbon solvent that is 35–40% aromatic or an oxygenated solvent such as alcohol or acetone. Mineral spirits mixtures that contain 35–40% aromatics can be used. Isopropanol is a good solvent that is less toxic to the user. A dilute (1:4) mixture of isopropanol in mineral spirits (15% aromatic) that lengthens working time can be useful. Arcosolv—also known as methyl proxitol, 1-methoxy-2-propanol, propylene glycol monomethyl ether—can be used but is polar and swells resins. Arcosolv has an evaporation rate similar to xylene but gives the sense of more working time due to its resin-swelling capacity. Slower evaporating mixtures increase the likelihood of re-dissolving underlying inpaint, so faster evaporating mixtures are useful when working on top of a layer of retouching.

iii. Modifications for special applications and effects (“Tricks of the Trade”)
Because these paints contain a resin that was designed to handle like natural resins, special effects and techniques, such as rubbing with powdered resin and polishing with a silk cloth, can be achieved.

The finely ground and evenly dispersed pigments produce very consistent brushstrokes. Fine details, such as eyelashes, ship rigging, and single brushstrokes, can be accomplished using Gamblin Conservation Colors. A fast evaporating solvent such as acetone is useful for these purposes as it avoids disturbing the inpainting underneath. Inpainting done in this manner produces an unblended or dry brush appearance. An acetone diluent can be used to create very fine brushstrokes that are also very matte.

Blending inpainting can be accomplished when Arcosolv is used as the solvent. Although Arcosolv evaporates quickly, it swells Laropal A-81 resin, giving the sense of more working time. However, using Arcosolv can also increase the likelihood of disturbing a lower layer of inpainting.

The addition of a few grains of powdered pigment can alter the texture to mimic the appearance of coarse or hand-ground colors. Added dry pigment can also be used to make the inpaint leaner and more matte.

iv. Tips on Use
Packaging: The supplied pigment and resin separate in their jars. For ease of use, the paints should be kept soft by adding a few drops of solvent (acetone or isopropanol) to the jars. According to Whitten, “Gloss matching and tinting strength are improved if you do not stir the paints. Use a swab stick to reach in and pull out the pigment paste and leave the resin in the jar. A small vial of resin and diluent can be placed on your palette for matching the gloss as you work. The colors are more useful on matte surfaces if the resin is not stirred in” (personal communication, November 26, 2008).

Some colors, especially cadmiums, dry out and may fall off a palette. To avoid losing paint cakes, place a drop or two of the resin solution underneath the color that has been withdrawn from the jar.

Diluents: The supplied resin solution (Galdehyde Resin Solution) initially resists the Arcosolv but is easily blended with a little extra mixing.

Manipulation of solvents for use on top of other layers follows the same paradigms as for other inpainting media. To avoid disturbing a lower layer of dammar, Paraloid B-72, RegalrezⓇ 1094, or Laropal A-81 varnishes, isopropanol is an appropriate solvent.

3. Health and safety
There are no special warnings for the dry resin, which has no travel restrictions and no flash point. Health and safety recommendations for the resin itself can be accessed at their website.

• Health: Exposure and first aid procedures should be determined by the solvent(s) used.

• Disposal: The paints should be allowed to dry out prior to disposal. Pigment content of some colors may determine special disposal requirements.

Note: the color chart included with this volume is a photographic reproduction of paint-outs. It was executed and provided by Gamblin Conservation Colors.

Sian Jones

Submitted June 2010

Polymeric Resins: Golden PVA

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Principal Name

Golden PVA Colors™

Other Names

Often referred to as PVA paints or, more correctly, as PVAc (to distinguish the poly (vinyl acetate) medium from polyvinyl alcohols).

History of Use

1. Industrial
While there is extensive use of PVAc resins in industry as early as 1930, Golden PVA Colors are specifically formulated for use by conservators and have no industrial or fine-arts related uses. (See Varnish catalog for base resin history of use.)

2. Conservation
Golden PVA Colors were formulated and marketed by Golden Artist Colors, Inc. in 1999 in response to conservators’ expressed need to have a commercially available PVAc-based inpainting medium. Prior to 1999, PVAc paints for inpainting were hand-made by conservators.

Source

1. Physical
Golden PVA Colors come in 1 oz. containers and are pre-mixed with ethanol, ¹⁰ PVAc resin, and one of 29 pigments.

2. Origins and Manufacture
Golden PVA Colors are available in 29 colors in addition to extender resin (see the paint-outs included with this volume). All colors are single pigments mixed with a very high pigment-to-resin ratio into PVAc resin dissolved in ethanol and mulled to a viscous consistency. Golden Artist Colors, Inc. has a long history of working with conservators and artists and is willing to make additional colors or paints upon request.

3. Manufacturers and vendors
Golden PVA Colors are a proprietary product manufactured exclusively by Golden Artist Colors, Inc. in New Berlin, New York. Vendors include most suppliers of conservation materials, including Talas, Conservation Resources, and Kremer.

Chemical and Physical Properties

1. Chemical classification
Base resin is 100 percent poly (vinyl acetate), thermoplastic solution polymer. Solution is a 1:1 ratio of AYAA and AYAC, dissolved in ethanol. ¹¹

2. Chemical formula/structure
(See varnish catalog for a more thorough description of base resin.) AYAA, and AYAC PVAc used in Golden PVA Colors are formed by free radical polymerization of vinyl acetate monomers. Resins are sold to paint manufacturers already polymerized in small beads that can be resolubilized in alcohols and mixed with pigments. The Golden Artist Colors, Inc. acquires PVAc resins from a variety of industrial sources; however, the average molecular weight of resins is 83,000 atomic mass units (amu) for AYAA and 12,800 amu for AYAC.

3. Solubility
PVAc resins are soluble in ethanol, and paint films remain soluble in ethanol after drying. Golden PVA Colors are also soluble in methanol, glycol ethers, ketones, and acetates. Golden PVA Colors are insoluble in glycols, hydrocarbons, propanol and higher alcohols, and water.

4. Tg
ACAA softens at 97ÅãC, AYAC at 71ÅãC; the Tg of paint is approximately 84ÅãC, depending on the pigment-to-binder ratio.

Preparation and Formulation

1. Typical preparation methods
Paints are manufactured and distributed in 1 oz. (30ml) jars. Paint is a viscous liquid in the jars. However, small amounts are usually taken from the storage containers and placed on a glass or ceramic palette to dry. Working with wet paints directly from storage jars is very difficult and often results in a thick, stringy, and difficult-to-match paint, therefore indirect application is recommended. A thin wash/layering application is generally most effective. Multiple layers can be built up quickly when rapidly drying solvents are used. It is possible, however, to resolubilize and pick up lower layers when building up colors, so isolating with varnish can often be useful.

2. Additives
Golden PVA Colors are composed of only PVAc resin, pure single pigments, and ethanol. Once dried on a palette, the paints can be easily resolubilized.

3. Storage/shelf life
Paint in jars can dry out if stored for a long time, but are easily resolubilized through the addition of ethanol. No special storage is necessary for jars or dry palettes.

Handling Characteristics

1. Appearance
Paint from the storage jar is a thick, viscous, intensely colored material. When dried on a palette, the paint is extremely hard and may appear somewhat matte to very glossy, depending on the colorant. The refractive index of base resin is 1.4665 (at 20ÅãC), making it somewhat similar to other acrylics and somewhat dissimilar to aged linseed oil. Depending on the amount of medium and solvent used, Golden PVA Colors dry to a matte through glossy appearance, although they tend toward the glossy end of the spectrum. Paint diluted with fast-evaporating solvents will often appear matte, while slow-evaporating solvents will result in a glossier sheen. Additional medium can be mixed with the paint to bring up a matte area of inpainting to the sheen of surrounding glossy paint without having to add additional varnish to the surface. Alternatively, paint from storage jars can be drained on a piece of FomeCor or absorbent board to achieve a very matte effect. The nature of the resin means that dark colors such as black or brown can often appear somewhat grey, dull, or milky in contrast to oil paint; however, according to Laura Hartman, the addition of Kremer dyes and/or dry pigments can create a more saturated appearance to these colors (personal communication, 2009).

2. Application
Paint dissolved in ethanol dries very quickly, making Golden PVA Colors good for delicate, thin layers of application. Working time can be extended by using slower evaporating solvents or solvent mixtures. The dried paint film is generally very durable, with excellent resistance to acids/alkalis, water, and ultraviolet rays. Film formation requires a minimum temperature of 9ÅãC; however, dried films can withstand freezing temperatures. Use of clean solvent seems to be more essential with Golden PVA Colors than with other inpainting choices, as the paint seems inclined to “cloud” easily. Meticulously clean solvent and judicious use of white seems to prevent this problem.

3. Modifications for special applications and effects (“Tricks of the Trade”)
Golden PVA Colors are very versatile and either can be thinned with solvent and mixed with additional medium for glazing effects or used at a thicker consistency to reproduce brushstrokes or trails of paint. The viscous nature of PVAc allows it to accept additives such as microballoons, ground glass, or additional pigments easily. It is an excellent choice for areas of inpainting requiring texture and bulk. One of the strengths of PVAc is that it is soluble in solvents completely different than those required for MSA colors and most varnishes. This property allows conservators to interlayer different inpainting systems without picking up previous layers. In addition, if conservators are unhappy with a session of inpainting, they can often remove the layer of PVAc media from a varnished or MSA inpainted passage without disturbing the lower paint or varnish (Brian Baade, personal communication, 2009). Golden PVA Colors’ greatest limitation is that a highly saturated black is difficult to match as it often appears cloudy or milky by comparison to the surrounding paint. The Quinacridone Gold color can be mixed with or layered over inpainting to give the appearance of an aged oil paint.

Aging Characteristics

1. Chemical process
PVAc resins are among the most stable available to conservators. Combined with high-quality, light-stable pigments, Golden PVA Colors should be expected to have very few visible or chemical changes. The base PVAc resin has shown little tendency to cross-link over time or in the presence of atmospheric pollutants, and chemical changes appear relatively minor.

2. Resultant chemical and/or physical alterations
PVAc can lose the appearance of saturation over time. However, given the high pigment-to-binder ratios in Golden PVA Colors and the usual thin layers of application, loss of saturation should be of less concern than the “graying” associated with some varnishes or surface coatings.

3. Impact on appearance, solubility, and removability
PVAc paints remain soluble throughout their lifetime, with few reports of reversibility problems associated with aging. If original paint is vulnerable to ethanol and inpainting still needs to be removed, toluene has also been reported to remove dried and aged PVAc films with success and less “stress” to the original paint (Joyce Hill Stoner, personal communication, 2009). A list of lightfastness, permanence, and opacity/transparency values for each color is available from the manufacturer.

4. Attraction and retention of dirt and grime
PVAc resins can remain somewhat tacky and soft, particularly in the presence of high temperatures and humidity. Golden PVA Colors are often applied under a final varnish coat of another material, so the attraction and retention of dirt and grime is much less problematic under these circumstances. Even in the presence of high temperatures and humidity however, retention of dirt and grime on thinly applied areas of inpainting is only a minor concern.

5. Theoretical lifetime
PVAc is a Class A material, so aging will be determined by the presence and behavior of any additives and the lightfastness of the pigments; however, inpainting is generally expected to age at a different rate than the original painting, regardless of inpainting material chosen.

Health and Safety

Golden PVA Colors are generally a very safe inpainting option for conservators. PVAc resin has few known health risks and, depending on the solvent used, provides a system that can be used in a public space with minimal ventilation. According to the MSDS that accompanies the paints, “Vapor may cause drowsiness and irritation of the respiratory tract. May cause nasal discomfort and discharge, coughing, possible chest pain.” As with any inpainting system, some pigments carry special handling/safety warnings.

Disposal

Brushes and palettes can be cleaned up using ethanol on paper towels or cotton. When the ethanol evaporates, the towels can be thrown in the regular trash, or if the pigments contain heavy metals such as cadmium, placed in marked containers for special pick-up. Empty containers of paint may be left to evaporate and dry in a fume hood and then placed in the regular trash if they contain non-toxic pigments, or marked for special disposal if they contain toxic pigments.

Tatiana Ausema

Submitted July 2009

Acrylics

Bocour Magna

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Principal Name

Bocour Magna

Other Names

“An acrylic resin formulated for artist’s use” [on tube].

History of Use

1. Industrial
Bocour Magna was developed by the American paint makers Leonard Bocour and Sam Golden in the late 1940s and marketed as “the first new painting medium in 500 years.” Bocour and Golden kept the pigment concentration in Magna deliberately high, so that the paint could be thinned with considerable amounts of solvent and still produce a saturated, intense color.

Roy Lichtenstein used it almost exclusively. It was also used by Kenneth Noland, Morris Louis, and others. A Robert Motherwell painting at the Metropolitan Museum of Art has the lettering “painted with Bocour Magna, do not clean with turpentine.” The artists liked its solubility in turpentine, its tinting strength, and the fact that it could be mixed with oil paints (Crook and Learner 2000, 25–27).

2. Conservation
The author has been using Magna for inpainting since 1969. She first made a palette of it on a plate of glass to use during a summer work project in Colonial Williamsburg. According to Robert Feller, it is a “true lacquer” paint, meaning it will always go back into solution and never polymerize. The author’s oldest Magna palette is still soluble in xylene.

Louis Pomerantz made a presentation on the use of Magna as his preferred inpainting medium in 1976 at AIC Dearborn in a panel organized by Peter Michaels (1976, 134).

Source

1. Physical
Bocour and Golden purchased the resin from Rohm and Haas.

2. Origins and Manufacture
Bocour made Magna beginning in the late 1940s. Bocour later sold Bocour Artist Colors, Inc. to Zipatone of Chicago, but they ceased making Magna paint in the early 1990s. Golden Artist Colors now produces a mineral spirit-borne acrylic paint called MSA Color, which is said to be similar to the original Magna, according to Crook and Learner, but Magna requires at least some xylene to go into solution, and MSA generally does not.

3. Manufacturers and vendors
It is no longer available; it used to be sold by Arthur Brown in New York City. Many people have stockpiled it.

Chemical and Physical Properties

1. Chemical classification
Acrylic resin

2. Chemical formula/structure
The Conservation & Art Material Encyclopedia Online (CAMEO) notes, “A brand name for a series of acrylic paints prepared from pigments dispersed in n-butyl methacrylate resins and diluted with turpentine, mineral spirits, xylenes, and toluene. The paints dry rapidly to a hard, matte, non-yellowing film.”

3. Solubility
Magna is soluble in xylenes and toluene, and it is said to be soluble in turpentine. Some colors are slowly soluble in petroleum benzene.

4. Tg
The Tg was unavailable at the time this volume was published.

Preparation and Formulation

1. Typical preparation methods
The author squeezes it from the tube out into a porcelain or glass palette. A dropper can be used to drip xylene onto it to soften it. It can be mixed on a temporary palette of foam board.

2. Additives
To increase gloss, add Paraloid. B-72 to the paints on the palette. This is generally needed for the dark colors but not for the lights. It can be drained on palettes of foam board to make it more matte.

3. Storage/shelf life
The author’s 1969 paints are still good. The tubes dry up but can be cut open and xylenes dropped onto them to make them usable.

Handling Characteristics

1. Appearance
Bocour Magna paints are not as glossy as PVAc or Gamblin colors. They are useful for inpainting tempera paintings because they dry matte. Bocour Magna paints are transparent, which can make it difficult to build up opacity. It is best to use them to glaze other media, applied more opaquely if opacity is required.

2. Application
As mentioned, Bocour Magna paints can be drained on foam board palettes to make them more matte. Paraloid B-72 in xylenes can be added to make them glossier.

The paint is readily soluble in itself so it must be applied in dots or tiny stripes that are allowed to dry before subsequent layers are added. It cannot be applied wet on wet. They are good for glazing on top of watercolor or tempera underpainting. They are readily portable, and the author has never found them to vary over the years.

Jim Bernstein recommends the following three diluent solutions:

1. To create a more matte finish:

Heptane	70 ml
Tolene	30 ml

2. For a slow evaporating diluent:

Petroleum Benzine	45 ml
Isopropanol	30 ml
1-Methoxy, 2-Propanol	10 ml
Shellsol 15	15 ml
Acetone	20 drops
Benzyl Alcohol	5 drops

3. For normal evaporation:

Petroleum Benzine	70 ml
Xylene	30 ml
Acetone	25 drops
Benzyl Alcohol	5 drops

Bernstein points out that the presence of xylene assists in staying close to the solubility center of most conservation resin paints, and he cautions users not to use a lot of xylenes when inpainting over resoluble low molecular weight varnish.

3. Modifications for special applications and effects (“Tricks of the Trade”)

Aging Characteristics

1. Chemical process
Dr. Feller said in 1970 that they do not polymerize or oxidize, etc., and remain soluble (personal communication, 1970). This appears to be true.

2. Resultant chemical and/or physical alterations
Bocour Magna inpainting on paintings treated 25 years ago by the author has not shown changes.

3. Impact on appearance, solubility, and removability
Very satisfactory.

4. Attraction and retention of dirt and grime
A painting the author treated 25 years ago was returned because it had been subjected to life with a heavy smoker. The Magna retouches absorbed more of the nicotine yellow than the surrounding Paraloid B-72 varnish and had preferentially discolored. It was all readily removable and replaceable.

5. Theoretical lifetime
The author has witnessed 40 years of Bocour Magna holding up well in normal conditions.

Health and Safety

(see varnish chapter for base resin)

The main problem with Magna is that it requires xylene as the solvent.

Disposal

As with other paint materials, follow local and federal disposal guidelines.

Joyce Hill Stoner

Submitted October 2003

Charbonnel

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Principal Name

Charbonnel restoration colors

Other Names

LeFranc and Bourgeois restoration colors; Charbonnel Colori per il restauro

History of Use

Charbonnel, originally LeFranc and Bourgeois, were intended from their creation for use in conservation/restoration. This line of paints was developed by LeFranc and Bourgeois in 1983 for painting restorers who wished to avoid the natural resins used in Maimeri formulation. The product was transferred to Charbonnel, which manufactured it until the late 1990s, after which it ceased being made.

Source

1. Physical
The manufacturer states that the paints are composed of pigments ground in acrylic and ketone resin binder, but analytical tests did not detect a significant ketone component (see below.)

2. Origins and Manufacture
The Lefranc and Bourgeois literature states:

“This medium…contains as much ketonic resin as acrylic resin (butyl methacrylate), dispersed in a heavy mineral spirit. The inclusion of ketonic resin allows for a high pigment content in these colors (mostly around 30% but sometimes up to 60% pigment)…the pigments used in this range are all used in our ranges of Artists’ Colors…The mineral pigments are basically oxides (Titanium, Zinc, Iron, Cobalt, Chrome), Cadmium selenides and sulfo-selenides, Cobalt aluminate and complex silicate of sodium and aluminum with sulfur. The organic pigments are essentially copper phthalocynine, azo and stable diazo, nickel azo, naphthol, quinacridone, thioindigo and alizarin. (Lefranc & Bourgeois, undated product information sheet).”

Colors for use in restoration; transferred to Charbonnel; discontinued.

3. Manufacturers and vendors
Not manufactured at present; still available from some conservation specialty vendors.

Chemical and Physical Properties

1. Chemical classification
Acrylic resin paint

2. Chemical formula/structure
Infrared spectra and nuclear magnetic resonance spectra performed by Dr. Crandall of Indiana University in 1984, together with reference spectra of B-67, identified polymethacrylate as the major component. The spectra generated did not show a significant influence of ketonic resin, if it is present. Dr. Feller ran tests the same year with similar results.

3. Solubility
Tests were carried out at Indiana University in 1984 with three sets of paintouts: one set was placed in dry heat at 70ÅãC for 54 days; another was placed face-up in a north-facing window; and a third was kept as a control in a dry drawer. Some of the dry-heat-aged colors became less readily soluble in petroleum benzine and heptane, with these solvents causing blanching. Solubility in VM&P Naphtha was slightly reduced, but xylene and toluene remained effective solutes and did not cause blanching. The daylight-exposed samples showed no changes in solubility.

4. Tg
The resin is assumed to have a Tg similar to the Tg of B-67, 50ÅãC, although paint-outs at 70ÅãC for 45 days did not deform, presumably due to the presence of pigment stiffening the paint.

Preparation and Formulation

1. Typical preparation methods
The vendors of these colors suggest in their catalogs that solubility in alcohol makes them ideal for inpainting. However, the relatively high polarity of alcohol makes it, in fact, a poor inpainting choice. Although the colors dissolve slowly in alcohol, the methacrylate binder is more soluble in aromatics or, when fresh, mineral spirits. To inpaint with these colors after they have dried out, mineral spirits with aromatics added are required. If the inpainter wishes to avoid the aromatic solvents, mineral spirit mixtures with 25 percent acetone work well.

Jim Bernstein likes the following solvent mixture:

Petroleum Benzine	70 ml
Xylenes	30 ml
Acetone	25 drops
Benzyl Alcohol	5 drops

He adds that the presence of xylene assists in staying close to the solubility center of most conservation resin paints. He notes, however, that conservators should avoid using too much xylene when inpainting on top of resoluble low molecular weight (LMW) varnish (e.g., RegalrezⓇ 1094.)

2. Additives
The authors do not use additives.

3. Storage/shelf life
When the Charbonnel retouching colors are stored at room temperature in their tubes with the tops tightly secured, they have a long shelf life. Although they dry out slowly in these conditions, tubes can last 25 years or longer showing only a moderate loss in working properties. If the colors do dry out, they can be reconstituted in mineral spirit mixtures containing either aromatics or acetone.

Handling Characteristics

1. Appearance
When the colors are first squeezed from their tubes, they have the paste-like consistency of any tube paint. When initially applied they appear glossy, but as the diluent evaporates, they dry quite matte. After the colors dry and are brought to the gloss of the surrounding paint by applying varnish, the resaturated color is usually slightly darker than the initially applied color.

2. Application
The Charbonnel retouching colors work like most other inpainting colors, in that they are usually applied with small brushes in a diluted form. They can be squeezed from the tubes in small dabs onto a palette and mixed by taking a little from each. When applied to the painting, they can be opaque or translucent depending on the pigments in the mixture or the thickness of application. Additional acrylic medium can be added to increase translucency and gloss.

To build up layers, either to make the application more opaque or to mimic the layer structure of the painting, an application of retouch can be varnished with a thin layer of PVAc in ethanol. This PVAc layer prevents the layer below from becoming disrupted by newer applications on top as long as its diluent is predominately aliphatic.

3. Modifications for special applications and effects (“Tricks of the Trade”)
Used straight from the tube and only slightly diluted, the colors have enough body to be helpful in hand texturing fills. They are particularly useful in applying a canvas texture to the narrow fills of a tear. A problem often encountered with texturing by hand is that the texture turns out too high. Because the Charbonnel texture shrinks appreciably on drying, this tendency is often overcome.

Aging Characteristics

1. Chemical process
Due to the inclusion of pigments, the cross-linking properties of the butyl methacrylate are mitigated (Dr. Feller, personal communication, 1984) and the paints should remain stable for a very long period (sufficient for use as an inpainting material).

2. Resultant chemical and/or physical alterations
In the twenty-five years since their introduction, no adverse chemical or physical alterations due to aging have been reported.

3. Impact on appearance, solubility, and removability
A slight matte appearance can develop over time if the paints are used straight from the tube, without added medium, and are not varnished or coated following use. The acrylic resin Paraloid. B-67 will yellow slightly with age, so it is possible these paints may also show a very slight yellowing.

4. Attraction and retention of dirt and grime
If the inpainted areas are not coated with varnish or some other resin, they may attract airborne grime due to the relative softness of the butyl methacrylate medium and the slightly rough surface.

5. Theoretical lifetime
More than 50 years.

Health and Safety

See Varnish volume of the PSG Catalog for base resins.

Disposal

As with any paints, the material is best disposed of as a dry film, after the solvent has evaporated.

Catherine A. Metzger and Michael Swicklik

Submitted January 2010

Golden MSA Conservation Paints

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Principal Name

Mineral Spirit AcrylicⓇ Conservation Paints

Other Names

MSA paints, MSA Colors, Mineral Spirit Acrylics. The term MagnaⓇ has also been used to refer to MSA Conservation paints. Although similar in formula, Magna was produced by a different (but related) manufacturer (Bocour Artist Colors, Inc.) and is described elsewhere in this volume.

History of Use

1. Industrial
MSA colors are produced exclusively for conservators and artists, however, the poly n- butyl methacrylate binder is used industrially (see Rohm & Haas product literature for more details).

2. Conservation
MSA Conservation Paints were first introduced to the art materials market by Golden Artist Colors, Inc. in the early 1980s as a custom product. They were reintroduced to the conservation field in 1994 as the successor of Magna colors after conservators suggested that they could be useful to the field.

Source

1. Physical
MSA Conservation Paints are composed of poly n-butyl methacrylate binder, pigments, and a thickener/rheology modifier (see “Chemical Classification,” below, for more details). The manufacturer provides 57 colors; in addition, custom colors are available upon request (see “Appearance,” below, for an example). The paints are sold in both one- and four-ounce glass jars with metal twist-off lids.

2. Origins and Manufacture
MSA Conservation Paints are manufactured exclusively by:

Golden Artist Colors, Inc.

188 Bell Road

New Berlin, NY 13411

Phone: (607) 847-6154

Toll Free: (800) 959-6543

Fax: (607) 847-6767

[http://www.goldenpaints.com Website}

The acrylic binder is manufactured by:

Rohm & Haas Company, a subsidiary of Dow Chemical Company

100 Independence Mall West

Philadelphia, PA 19106-2399

Phone: (215) 592-3000

Fax: (215) 592-3377

Website

The thickeners/rheology modifier, called Thixcin. R, is manufactured by:

Elementis Specialties, Inc.

P.O. Box 700

Wyckoffs Mill Road

Hightstown, NJ 08520

Phone: (609) 443-2000

Fax: (609) 443-2422/2201

Website

3. Manufacturers and vendors
Golden MSA Conservation Paints are distributed by:

Conservation Support Systems

Santa Barbara, California

Website

New York Central

Website

Talas

New York

Website

The Italian Art Store

Morristown, New Jersey

Website

Chemical and Physical Properties

1. Chemical classification
The poly n-butyl methacrylate binder is supplied by Rohm and Haas Company as 40% solids in 54% mineral spirits (Stoddard Solvent, which is typically 15–20% aromatic) and 6% Aromatic 150 (high flash aromatic naphtha, type II, aromatic 150, which is typically 98% aromatic). The residual acrylic monomers from the polymerization of the binder comprise < 1.0 wt. %. Initiators and chain transfer agents are also added, but the polymer manufacturer did not report further information.

The paint manufacturer adds pigments (see list of pigments under Chemical Process, below) and a thickener/rheology modifier, which is an organic derivative of castor oil (trihydroxystearin) called ThixcinⓇ R, by Elementis Specialties, Inc. No ultraviolet radiation stabilizers, preservatives, or freeze-thaw stabilizers are added by the manufacturer. Since the introduction of MSA paints, no changes have been made to the formulation that affect the application/solubility characteristics.

2. Chemical formula/structure
Please note that the chemical formula for Thixcin, the main additive in the Golden MSA Conservation paints, is proprietary and could not be obtained for this paper. The chemical structure of Poly n-butyl methacrylate follows:

Figure 4 Chemical structure for Aquazol, Elizabeth Jablonski and Matthew Skopek

3. Solubility
The manufacturer recommends using mineral spirits (but not “odorless” or “low odor”) to thin the paints and resolubilize them after drying. However, conservators have found that a solvent with a higher percentage of aromatics (from 10% to 50%) is often needed to re-solubilize them after they are dry and to attain a fluid consistency that flows from the brush easily. Stoner (personal communication, 2008) suggests 80% petroleum benzine and 20% xylenes. Pollak (personal communication, 2008) uses a xylene/benzine mixture, with small amounts of benzyl alcohol and acetone added.

The manufacturer also reports that artists have found that lower layers of MSA paints are sometimes resolubilized under subsequent applications of the paint, during the process of creating a painting. This is undesirable because it inhibits the creative process for the artist. In an ongoing study by the manufacturer concerning the resolubility of certain colors of MSA paints, younger paint films (24 hours old on glass substrates) are slightly more quickly resoluble in Stoddard solvent than older paint films (3–12 years old on laminated cardstock). However, the study also shows that the paint films are even more quickly resoluble in solvents with higher aromatic content than in Stoddard solvent alone. The solvents included in the test are (1:3) Stoddard:xylenes; (1:1) Stoddard:xylenes; and xylenes, neat (Golden Artist Colors, personal communication, 2006). Details of the study can be obtained from the manufacturer.

As a remedy for unintended resolubilization of lower layers by upper layers, the manufacturer recommends that artists apply their product, the waterbased Golden Polymer Varnish, in between layers to act as an isolation layer (Golden MSA 2010). At the time of this research, however, no conservators had reported using this technique.

4. Tg
The glass transition temperature of the poly n-butyl methacrylate binder is 20° C.

Preparation and Formulation

1. Typical preparation methods
Conservators typically remove a small portion of paint from the glass jar packaging, as supplied by the manufacturer, and place it onto a palette. If the paints are not used immediately, they are left to dry on the palette and are resolubilized when needed. Conservators typically apply the paint by brush, but it can also be sprayed (see Application/Modifications for Special Applications and Effects, below, for more information).

2. Additives
See Chemical Classification, above.

3. Storage/shelf life
The manufacturer recommends that the consumer avoid freezing the product. The paint should be applied at temperatures above the Minimum Film Formation Temperature of 48ÅãF/9ÅãC.

The manufacturer does not foresee a limit to the shelf life of the product. Conservators have observed that the solvent can evaporate over time, but that the binder and pigment remain blended and do not separate. The manufacturer recommends keeping the lids on tight to help retain the solvent. It was the empirical observation of one of the authors that different colors dry out in the manufacturer’s packaging faster than other colors. Stored together in an air-tight box, the following colors exhibited varying degrees of solvent retention (although it was acknowledged that some jars were probably more tightly sealed than others and that the purchase dates of each color may have varied):

Quantity of Solvent (Empirical Observation)	Names of Colors in Jars
Retaining the most solvent	titanium white and titanium buff, mars black, dioxazine purple, quinacridone crimson, raw sienna, cadmium orange, yellow medium, and red medium, and cerulean blue
Slightly dry	yellow ochre, burnt sienna, ultramarine blue, cobalt green, and permanent green light
Drier	raw umber and cadmium yellow light
Driest	bone black

Handling Characteristics

1. Appearance
The MSA paints have a matte to satin appearance when applied thin and a satin sheen when applied with a higher impasto. All colors are slightly glossier when wet than when dry. The various colors have different opacities in accordance with the characteristics of each specific pigment, as they would in oil paint. It should also be noted that the materials and texture of the infilling and isolation layer to which the paints are applied may also affect their appearance.

When fresh from the jar, some colors are stringy, although they become workable with the proper solvent, whereas other colors are buttery and can be directly shaped into impasto. Conservators have found that the pigments are finely ground, contributing to the smooth, even consistency when diluted with solvent.

Dried MSA paints are slightly glossier than other inpainting materials, such as Magna and Lefranc & Bourgeois Charbonnel colors, but are still selected by many of the conservators surveyed for this paper for their good match to matte and unvarnished modern paintings, where they do not require gloss adjustment or varnish on top. However, a recent study by Sims et al. , in which a wide variety of inpainting media were tested specifically for matching acrylic emulsion paintings, suggested that achieving a perfect match to acrylic emulsions with solvent-borne acrylics is difficult, although perhaps can be achieved with more experience in using the medium. Sims et al. also noted that the paints are translucent when thinned and were not opaque enough to cover a mark in their test paintings, but suggested that this translucency may be useful in other applications.

One of the authors recently purchased custom colors to match specific areas in a modern painting. In this case, the manufacturer matched the colors of the painting through the use of colorimeter readings. Drawdowns were sent before the finished product to confirm the color match. Using the paint wet from the jars was possible, as they had a more buttery consistency. Used this way they dried to a slightly higher gloss than when applied thin, although likely to a comparable level as would be seen with the buildup of multiple thin layers.

2. Application/Modifications for special applications and effects (“Tricks of the Trade”)

Increasing gloss
The surface sheen of MSA paints can be increased with the addition of varnishes while in the wet state, such as ParaloidⓇ B-72 (Stoner, personal communication, 2008); Paraloid™ B-67 (Pollak 2008); or Winsor & Newton matte or gloss varnish.

Adding varnishes on top of dry MSA paints, either locally or over the entire painting, will also increase gloss. Some conservators find that varnishing is not always necessary, although dammar, Regalrez., MS2A and Golden MSA Varnishes can be sprayed over the surface. Stoner (personal communication, 2008) notes that a thin layer of MS2A is an option and localized application with silk or an inpainting brush can achieve a gloss appropriate for 17th- or 19th-century paintings, although perhaps a glossier inpainting medium should be chosen to begin with for these types of paintings. Pollak (2008) has locally brushed on Paraloid B-72 and B-67. Both Pollak (2008) and van Gelder (personal communication, 2008) have sprayed on 10% concentrations of Paraloid B-72, overall. Conservators have also brushed and sprayed Regalrez overall in 10–15% concentrations.

Matting
The gloss of the MSA paints can be reduced by draining colors on a Fomecore . palette (Stoner 2008). In fact, Stoner (2008) stressed that, “It’s not so much whether they are thickly or thinly applied but how you drain and dilute them before applying.” Pollak (2008) has added fumed silica for matting. It was noted by van Gelder (2008) that the more the paints are diluted with solvent, the less glossy they will appear upon drying.

Spray application
The manufacturer suggests that artists can apply MSA paints by spraying. They suggest that the paints be blended with Golden MSA Varnish in 10% increments to attain the desired color intensity and then diluted with an equal amount of mineral spirits. They recommend using airbrushes without “O-rings” that could react with solvents (Golden MSA Conservation Paints). MacDowell (personal communication, 2009) reported having applied the MSA colors to ceramics by spraying with an airbrush and then sealing with a clear coating for durability.

Adjusting working properties and translucency
Stoner (2008) notes that acrylic gels can also be used over or under the MSA paints for other desired effects. The manufacturer recommends blending MSA paints with Golden MSA Gels and MSA varnishes to adjust consistency and translucence.

Aging Characteristics

1. Chemical process
Over the last 50 years, there has been a significant amount of research on the poly n-butyl methacrylate binder of the MSA paints, and ongoing research continues to advance our understanding on this material. Epley provided a summary of the information available to that date. The research suggests that the resin does have a slight tendency to cross-link and become insoluble, especially under accelerated aging. It is not currently known how the addition of pigments and additives may affect these processes.

2. Resultant chemical and/or physical alterations
Under natural and light-aging, Sims et al. noted a darkening and cooling of the color of Golden MSA Quinacridone Red and a lack of change in the Titanium White. These were the only two colors noted in the study.

The manufacturer has tested the lightfastness of the MSA paints under extreme conditions, while under glass and under direct exposure to outdoor conditions. The lightfastness of the various colors ranges from excellent to fair (a change of zero to eight units on the CE 1976 L*a*b* color difference scale), with the exception of Cadmium Yellow Primrose, which was poor (a change of over 20 units). The following is a table of the results):

MSA Colors - Lightfastness Results
Anthraquinone Blue	4.3	Mars Black	0.26
Bone Black	4.3	Mars Yellow	0.66
Burnt Sienna	0.26	Naphthamide Maroon	3.3
Burnt Umber	0.6	Napthol Red Light	3.1
Burnt Umber Light	0.97	Napthol Red Medium	5.7
Carbon Black	0.53	Nickel Azo Yellow	3.2
Cerulean Blue	0.37	Pthalo Blue G/S	1.4
Chrome Oxide Green	0.28	Pthalo Blue R/S	1.5
Cadmium Orange	7.3/.112	Pthalo Green B/S	0.74
Cadmium Red Dark	3/.37	Pthalo Green Y/S	0.72
Cadmium Red Light	5.6/.33	Pyrrole Red	0.55
Cadmium Red Med	4.5/.37	Quin. Burnt Orange	2.6
Cadmium Yellow Dark	NA/.35	Quin. Crimson	1.9
Cadmium Yellow Light	13.5/.39	Quin. Gold	2.6
Cadmium Yellow Med	11.1/2.1	Quin. Red	2.7
Cad Yellow Primrose	20.3/.4	Quin. Red Light	1.5
Cobalt Blue	0.36	Quin. Violet	2.1
Cobalt Green	0.42	Raw Sienna	0.34
Cobalt Titanate Green	0.67	Raw Umber	0.47
Cobalt Turquoise	1.27	Red Oxide	0.44
Diarylide Yellow	1.3	Titanate Yellow	0.38
Dioxazine Purple	5.3	Ultramarine Blue	1.7
Green Gold	2.9	Vat Orange	1.4
Graphite Gray	0.61	Violet Oxide	0.53
Hansa Yellow Med	6.2	Yellow Ochre	0.54
Hansa Yellow Light	2.25	Yellow Oxide	0.75

Testing followed the protocol of ASTM Test Methods for Lightfastness of Pigments Used in Artists’ Paints (D 4303), Test Method A. Samples are reduced to tints of 40% reflectance and exposed in southern Florida outdoors, under glass, at a 45Åã angle facing the equator. Exposure duration is 3–4 months, for a total radiation dose of 1260 MJ/m2. Samples were measured before and after exposure (specular reflection excluded). In accordance with the CE 1976 L*a*b* color difference equation, color change is stated in terms of total color difference units ΔE*. Changes of up to 4 units are considered excellent to very good, 4–8 units are very good to fair. As a point of reference, a true Alizarin Crimson tested at the same time had a color change of 17.46 units.

Cadmium pigments are not lightfast under the extremely humid conditions of outdoor exposure testing. They have been found to have excellent light fastness when tested under conditions of accelerated exposure with relative humidity controlled to normal levels (50–60%). The second figures (e.g., 7.3/.112) in the table for the cadmium colors represent changes measured after 400 hours of UVA-351 fluorescent lamp, simulated daylight exposure.

Disclaimer: The above information is based on research and testing done by Golden Artist Colors, Inc., and is provided as a basis for understanding the potential uses of the products mentioned. Due to the numerous variables in methods, materials, and conditions of producing art, Golden Artist Colors, Inc. cannot be sure the product will be right for you. Therefore, we urge product users to test each application to ensure all individual project requirements are met. While we believe the above information is accurate, we make no express or implied warranties of merchantability or fitness for a particular purpose, and we shall in no event be liable for any damages (indirect, consequential, or otherwise) that may occur as a result of a product application.

3. Impact on appearance, solubility, and removability

i. Appearance: The color changes in the paints, when tested for lightfastness, as reported by the manufacturer, may not be perceptible to the human eye. However, as stated in the section on Chemical Process above, the poly n-butyl methacrylate resin alone has been shown to crosslink and become insoluble upon accelerated aging; the paint with added pigment and other additives was not tested for solubility and reversibility. Sims et al also noted that the color shift in the MSA Quinacridone Red was very slight.

ii. Solubility: As Feller and others have noted, aging processes do not necessarily inhibit later removal until they have reached a very advanced state. According to Feller, while solubility will be affected, swelling and removal should be possible up to the point that the film has become 90% insoluble. Sims et al. noted that the light-aged samples in their study took longer to solubilize than the naturally aged samples and perhaps this is a result of polymerization upon aging.

iii. RemovabilityNone of the conservators surveyed for this entry reported having to reverse aged MSA paints inpainting. Anecdotal evidence from multiple sources suggests that MagnaⓇ, which was also a homopolymer of pnBMA, remains very easy to reverse at this time.

4. Attraction and retention of dirt and grime
In general, it has been suggested that the relatively low glass transition temperature, molecular weight, and minimum film formation temperatures can cause a solvent-borne acrylic film to remain tacky at room temperature and attract and retain dirt. However, compared with acrylic emulsions, it remains harder and will be less likely to absorb dirt over time. Another factor is that a high pigment load could produce an uneven surface, offering minute places for dirt to lodge.

The development and retention of static charge has long been suggested as another possible drawback, but has only recently been tested: Abbott and Smith showed that MSAs tend to hold a charge at low RH for longer than many other paint mediums, although these charges were found to dissipate after a few hours at most.

Pollak (2008) noted that the dried MSA paints on palettes do not seem to absorb dirt. One of the authors’ observations of thickly applied Magna on paintings dating from the late 1950s showed no current absorption of dirt by the surface. Stoner (2008) reported finding that the 20-year-old Magna inpainting (a product similar to Golden MSA Conservation Paints) on a painting in a home with smokers had preferentially absorbed grime, but was readily removed.

5. Theoretical lifetime
The theoretical lifetime for Golden MSA paints has not been tested. However, paintings created with Magna, a similar product, by artists such as Morris Louis (American, 1912–1962) and Roy Lichtenstein (American, 1923–1997) have been examined by conservators over the years. Ausema (personal communication, 2010) reports that, based on observational study of color field paintings employing Magna, the paint appears to have excellent color fastness and that the binder is very stable even when heavily diluted.

Health and Safety

See the manufacturer’s Materials Safety Data Sheet on Golden MSA Conservation Paints for further details.

Disposal

Disposal of MSA paints primarily pertains to heavy metal-containing proprietary materials. Refer to the disposal rules of the region in which the paints are used.

Elizabeth Jablonski and Matthew Skopek

Submitted December 2003

Acryloid B-72 Resin-Based Inpainting Material

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Conservators began using Acryloid B-72 as an inpainting medium almost as soon as the resin became available to them in the 1960s and 1970s. The hand-ground paints had the same drawbacks as did any hand-made paint. Eventually, conservators sought inpainting colors that offered evenly dispersed pigments in the chemically stable resins they had been using. The production of Acryloid B-72 Color Chips was announced to conservators in 1993. The colors were not made specifically for conservators but came from another application (an urban legend via Scott Blair of Conservation Support Systems suggests that the colors were made for pinball machines). Over ten years later, in 2006, the German company Kremer Pigments, Inc. began making Kremer Retouching Colors specifically for conservators using pigments commercially ground in B-72. This product was a logical addition to Kremer’s offerings, as B-72 had been a more widely used retouching medium in Britain and other parts of Europe. Kremer had been carrying B-72 since 1980 and considered it the most important acrylic resin for “…retouching paint in conservation”. Website

Acryloid B-72 Color Chips

Development and formulation

Acryloid B-72 Color Chips were an early introduction into the commercially prepared inpainting color palettes, but they are not widely embraced by paintings conservators as there have been very few references to the colors in conservation literature. The chips may see more use for conservators of wooden artifacts. The supplier reports that they are popular in Europe where they are used as a filling material as well as for toning or inpainting.

Their production was announced in the January 1993 issue of the WAAC Newsletter in the Technical Exchange pages. According to the announcement:

“Quaker Color in Quakertown, Pennsylvania (215-536-3520) makes pigment dispersions. They currently grind about 30 different pigments (from Ciba Geigy, etc.) in Acryloid B-72 using a differential roll mill, aiming for a 7–8 grind (Hegmen gage) or about 6.4 microns. This is much finer than pigments can be ground dry. These pigment dispersions are sold as dry chips of pigment in varying percentages of B-72. They are soluble in acetone; however, a few drops of toluene will dissolve them more completely, producing transparencies without flecks of pigment. .”

The sole supplier of Acryloid B-72 Color Chips—Conservation Support Systems—explains that

“Acryloid B-72 color chips are made by the dissolving of Acryloid B-72 resin in toluene and then color blended with the finest lightfast pigments on a three roll mill. Once the color is fully blended, the solvent is then evaporated from the processed mixture. The resulting dry material is then crushed, producing color chips that vary in texture from a very coarse powder to chips approx. 1/8”-1/4” in size. Acryloid B-72 color chips have a pigment concentration of approximately 32–38% with the balance being Acryloid B-72 resin (a small percentage of 1–2% of toluene may be present). They are great for inpainting, as a solid colored filling material, making colored marking solutions and much more... ”

The Color Chip palette includes 23 colors, which utilize natural pigment for some colors and organic colorants for others. Conservation Support Systems, the supplier, lists them on its website. In 2009, the supplier reported that the color chips were becoming increasingly difficult to get from their supplier, who was demanding larger quantity minimum orders for repackaging (personal communication, July 21, 2009).

Handling Characteristics

1. Appearance
The Color Chips dissolve into very fine pigment dispersions. The paints have high tinting strengths to produce highly chromatic pure colors. The fine colorant particle size enables thin, transparent washes of color. The large molecule size and relatively low refractive index of the Acryloid B-72 (~1.489) contributes to the perception of poor saturation in the dark colors. However, the stability of the resin promises clear, bright whites and light colors that are unlikely to discolor. The red palette needs supplementing with true reds, such as the cadmium pigments. The transparent colors (e.g., Thioindigoid Red) are useful glazing materials. The blue palette lacks a cerulean color, and the two green colors offered are phthalocyanine greens, which are difficult to use without significant manipulation. The palette may be more useful for modern and contemporary paintings.

2. Application
The Color Chips are easiest to use when a small amount of chips (of a single color) are placed in a storage palette that has pans or wells. The chips can be softened with solvent in the well where they will become workable and then dry out again to become a “cake” of color. They could probably be effectively used as pure colors placed straight on a working palette, but the dry “chip” form needs anchoring on the palette with a little solvent, or solvent and medium. Several colors of dry chips can be dissolved and mixed together for cakes of custom colors.

The paints dry to a satin gloss finish when used without additional medium. Some color shift is apparent when varnish is applied over them, but if the color is matched when wet, it will match again, after varnishing. The surface gloss is especially easy to match when a final application of Acryloid B-72 varnish is used.

3. Modifications for special applications and effects (“Tricks of the Trade”)
The paints can be manipulated in the same manner as other inpainting media. Fast evaporating solvents permit crisp touches of color over another color. Slower evaporating solvents can allow for some blending. Additional medium will make the colors glossier but only as glossy as Acryloid B-72 itself. Additional dry pigment can create a very matte and dry appearance. If the added dry pigment is coarsely ground, the resulting paint will also appear rough textured. (I don’t know about creating impasto with it, but am looking for others who may use it in this manner.)

The Acryloid B-72 Color Chip palette has quite a wide range of transparent synthetic colors that enhance the use of refining inpainting with glazes.

Health and Safety

The paints carry the same warnings as their components. The chosen solvent determines the paint’s handling and disposal requirements. Some pigments that are inherently toxic carry additional warnings.

CSS Restoration Colors 1. Development and Formulation
These are tube colors that contain approximately 30–32% pigment content in approximately 12–20% resin solution. They are also supplied by Conservation Support Systems. The CSS Restoration Color palette has exactly the same 23 colors as Acryloid B-72 Color Chips because they are actually the same base material that has been redissolved into a paste and inserted into tubes. Although still listed in Conservation Support Systems’ catalog, inventory in early 2010 was small. Low demand had not warranted replacement of inventory and the effort associated with their production (Scott Blair, Conservation Support Systems, personal communication).

Kremer Retouching Colors for Conservation 1. Development and Formulation
In 2006, Kremer Pigments acquired a grinding mill for mixing commercially ground paints. The company produced concentrated pigment paste colors, or “semi-dry pastes,” using historic pigments ground in 50% solids B-72 resin dissolved in toluene. The colors are normally supplied in 3ml glass jars with snap caps. Larger quantities are available upon request. The colors are marketed in two palette groupings. The colors come in a wooden box that holds the jars upright.

The two palette groupings have 27 colors each, 17 of which are repeated in both palettes. A total of 37 colors ground in B-72 are made. Most colors are the historic pigments that conservators are familiar with. The majority of the pigments are natural, except for a few historic substitutes, e.g., madder lake. The listings for many of the colors include pigment particle sizes or ranges. The palette range includes traditionally opaque and transparent offerings.

2. Handling Characteristics
The colors can be used straight from the jar by adding a few drops of solvent to the glass. Small amounts of the paste colors can also be removed from the jar, allowed to dry on a palette, and then redissolved for use. The manufacturer recommends acetone, toluene, and Shell Sol A as good solvents when using the colors for inpainting. To redissolve the colors in their jars, acetone, ethyl acetate, Shell Sol A, toluene, or xylene can be used.

The paints can be used as stand-alone inpainting, as a foundation layer, or as glazes. Because the colors have been machine ground, the paste is smooth and consistent, with good hiding power. Many effects can be mimicked by altering the amounts of pigment, solvent, and medium used. Little medium and a fast evaporating solvent such as acetone can produce fine dry brushwork. Additional medium can be mixed with the finely ground pigment to thin it for use as a transparent glaze. Careful choice of solvents can help prevent disturbing lower layers of B-72 inpaint. A local isolating layer of a different varnish that is more polar can also be helpful to achieve manipulations to the upper layers without disturbing those below.

3. Health and Safety
The solvents used with B-72 carry health and safety warnings. Kremer’s website provides links to the PDF Material Safety Data Sheets for acetone, toluene, and Shell Sol A. The solvents used should determine health and safety guidelines. Many historic pigments, especially those that contain lead, mercury, and chromium, carry their own hazards. Before disposal, the paints should be allowed to dry out and be removed according to local regulations.

Sian Jones

Submitted March 2010

Synthetic Resin Emulsions

Flashe (PVAc)

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Principal Name

Lefranc and Bourgeois (now known as Charbonnell) Flashe Vinyl Colors

Other Names

None

History of Use

1. Industrial/Artistic
Dominique Rogers writes (personal communication, March 3, 2004) that her experience working with Flashe as a ghost for the Op artist Victor Vasarely gave her some valuable insights into the medium: “All of his studio paintings were made with Flashe (Lefranc and Bourgeois) on canvas or cardboard. Good points: the colors, as long as you follow the star system and do not use color with less than 3 stars, have shown a good lightfastness. They are easy to mix, and I have not found anything else that gives such a flat, uniform, matte surface. Bad point: the surface created is fragile to the touch or even the breath.”

According to the Lefranc and Bourgeois website:

“The FLASHE range, distributed since 1954, is one of the first modern painting materials to give artists other means than oil painting to express themselves. Its optical characteristics allow the effects of old tempera paints and primitive painting grounds to be reproduced. Matte and velvety, opaque.

FLASHE colours are diluted in water and become indelible when dry.

FLASHE colours are applied using brushes, paint guns, or sponges.

FLASHE is a multi-purpose product with many uses: Preparing grounds for using oil or acrylic paints, creation of canvas paintings, theatre sets, advertising decors, thumbnail sketches, or trompe l’oeil drawings.

For these many techniques, FLASHE has a palette of 84 colors (35 new colors since 2007) that can all be mixed together. FLASHE is available in 60ml tubes (40 shades), 125ml glass jars (77 shades), 400ml glass jars (49 shades), and, on request only, 5kg pails (40 shades). Website .”

2. Conservation
Flashe colors were initially used in objects conservation, often on modern sculpture. Gerri Ann Strickler, Object Conservator at the Williamstown Art Conservation Center, is recorded as having used them as retouching medium on two Calder mobiles in 1983 (Julie Wolfe, Getty Museum, personal communication, January 26, 2004). In addition, Object Conservator Wolfe used them on modern sculpture while employed at the Guggenheim Museum (Wolfe 2004). Flashe colors are currently being used on the Vermont Museum and Gallery Association Painted Theater Curtain Project for retouching. They closely emulate the matte appearance of the original distemper (estimate) paint layer. Andrea Guidi di Bagno, Chief Conservator, Paintings, at the Museum of Fine Arts, Houston, originally used Flashe colors in France in the 1970s as an underlayer for final inpainting, which would be completed in another medium. In this work, her palette was limited to Indian red, a black, and a white. She also has used them currently in the conservation of the work of Carlos Cruz-Diez. They are the preferred method of retouching on some of his work from the 1950s where he used Flashe himself (personal communication, Guidi di Bagno, 2010).

Flashe colors were used on a Rex Whistler mural in the mid-1980s in the collection of the Tate Gallery, Millbank site. Roy A. Perry, conservator at the Tate Gallery, recounts using the colors on the flood-damaged painting and states that using Flashe was “not the answer to our prayers (nothing was)” (Perry, personal communication, March 22, 2004). He states that although the color changing on drying is perhaps not as unpredictable with Flashe as with an acrylic medium, it can be counteracted by allowing the color to dry out and then redissolving it using an appropriate solvent, such as 1:1 mix of petroleum spirit and isopropanol or similar alcohol or a high aromatic content hydrocarbon. Additional medium can also be added simply by the addition of poly (vinyl acetate) (PVAc) resin, which can be acquired from most conservation material suppliers. He goes on to add that Flashe can crack over slick films as it shrinks on drying and, being brittle, is only suitable on fairly rigid, stable surfaces. He also notes that its solubility changes over time may require solvents that would affect many modern paints. These solvents include aromatics such as xylene and toluene.

Source

1. Physical
Flashe vinyl colors are a poly (vinyl acetate) (PVAc) copolymer emulsion introduced in 1954 by Lefranc and Bourgeois (founded in Paris, France in 1720).

2. Origins and Manufacture
ColArt (Winsor and Newton) now works with Lefranc and Bourgeois, who created the colors. The chief paint formulator at Winsor and Newton offered this: “Flashe [paints are] based on a vinylacetate copolymer emulsion. They are formulated to give a flat matte finish” (via Mark Gottsegan, ASTM Scientist, February 3, 2004). They are currently manufactured by Winsor and Newton.

3. Manufacturers and vendors
Flashe vinyl colors can be purchased directly through Winsor and Newton but are also available through a variety of online vendors.

Chemical and Physical Properties

1. Chemical classification
Aqueous poly (vinyl acetate) (PVAc) copolymerized with ethylene and/or acrylic acid.

2. Chemical formula/structure

Figure 5 Chemical structure for Aquazol, Courtesy of Erica James

3. Solubility
Dominique Rogers writes that Flashe paints were “easy to remove in acetone” (personal communication, March 3, 2004). In addition, Gerri Ann Strickler noted in 1983 that Flashe paints were “partially soluble in toluene and ethanol (separately) and soluble in xylenes as well as acetone” (Wolfe, personal communication, 2004).

Roy A. Perry also adds that its solubility changes over time may require solvents that would affect many modern paints (Perry, personal communication, March 22, 2004). The chief paint formulator at Winsor and Newton stated, “I would expect [Flashe colors’] removability to be similar to acrylic emulsions, which also get used by restorers” (via Gottsegan, 2004).

4. Tg
The glass transition temperature for PVAc will vary from 16–26ÅãC.

Preparation and Formulation

1. Typical preparation methods
In conservation, Flashe is applied with a preferred inpainting brush, such as Winsor Newton Series 7. It is used like any other inpainting medium and is available in tubes (60ml); jars (125ml and 400ml); and pails (5kg custom order). The custom-ordered pails are used in artistic ventures, such as mural work, where the paints can be applied with a roller and the method of application is less critical. In conservation, jars are the most economical method of purchase. The paints are used straight from the jar and, ideally, a small amount can be placed on a palette with a small amount of poly (vinyl acetate) medium added if additional gloss is required. If additional gloss is required, the poly (vinyl acetate) medium type can be varied between AYAA, AYAC, and AYAF.

2. Additives
Proprietary

3. Storage/shelf life
In my experience, Flashe colors have a shelf life of no more than a year if not stored under ideal circumstances. These circumstances include dark storage at room temperature with the lids on. Once they are stored for a long period of time, opened and closed continually, or used in environments with varying climates, the components start to separate and it becomes more difficult to achieve the initial texture. Some colors are more likely to have separated than others depending on their initial formulation. In the author’s experience, the reds and yellows are more likely to separate.

Dominique Rogers states (2004) that “mixtures can be kept in pots forever (I have some that are 15 years old) as long as you top them up with water from time to time or have very well-sealed pots.”

Handling Characteristics

1. Appearance
Flashe vinyl colors are formulated to give a matte, opaque finish with high hiding power.

2. Application
Flashe pigments are applied in the same manner as other retouching mediums and can be used with synthetic or natural hair brushes. They do, however, work best with a synthetic hair brush.

3. Modifications for special applications and effects (“Tricks of the Trade”)
Andrea Guidi di Bagno mentions that mixing the paints on a piece of rigid MylarⓇ is ideal: “As Flashe paints dry quickly in a film and are difficult to reconstitute, unlike a medium like Maimeri, it is best to use them sparingly. The residue can be released quickly from the Mylar with minimal waste” (Guidi di Bagno, 2010).

Aging Characteristics

1. Chemical process
Unknown; proprietary

2. Resultant chemical and/or physical alterations
See directly below.

3. Impact on appearance, solubility, and removability
Julie Wolfe states the following:

“In April-July 2000 at the Guggenheim Museum, I purchased a lightfastness testing kit which tests to ASTM D 5398. I tested 18 colors and found that all but 4 colors appeared to be lightfast. The tyrian rose and brilliant orange permanently faded. In contrast, the red vermillion and orange actually darkened slightly. Colors tested were white, yellow ochre, gold yellow, brilliant orange permanent, orange, red vermillion, tyrian rose, carmine red, green oxide of chromium, chrome green, electric blue, sepia brown, black, raw umber, and ultramarine blue..”

4. Theoretical lifetime
Lefranc and Bourgeois makes no claim to the shelf life of Flashe vinyl colors. The colors should be well sealed and stored in dark storage to maximize shelf life.

Health and Safety

(See Gianfranco Pocobene’s article, “Poly (vinyl acetate)” in Volume 1 of the Painting and Conservation Catalog: Varnishes and Surface Coatings, p. 198.)

Poly (vinyl acetate) is a nontoxic material that is approved by the FDA for the packaging of food. Many of the solvents that are used to dissolve PVAc are toxic. MSDS should be referred to when dissolving the resin.

Disposal

(See Gianfranco Pocobene’s article, “Poly (vinyl acetate)” in Volume 1 of the Painting Conservation Catalog: Varnishes and Surface Coatings, p. 198.)

PVAc resins are to be disposed of by incineration in a furnace or otherwise disposed of in accordance with the appropriate federal, state, and local regulations.

Erica James

Submitted June 2010

Golden, Permanent Pigments (PVAc Emulsion)

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Principal Name

Golden Heavy Body Acrylics

Other Names

Goldens: Golden’s Acrylics

Under the heading of Golden Heavy Body Acrylics (GHBA), the company includes Historical Heavy Body Acrylic Hues, Iridescent/Interference colors, Neutral Greys, Acrylic Matte Colors, Fluorescent Acrylic Colors, and Phosphorescent Green. Compatible with the Golden Heavy Body Acrylics are Golden’s line of Airbrush Colors available in opaque and transparent color sets. There is also a range of gels and mediums that alters the gloss and thickness of the acrylic paints.

History of Use

1. Industrial
Golden Artist Colors are produced primarily for artists. The Heavy Body Acrylics were introduced in 1980. Initially they were sold directly to artists in large containers in a limited geographic area. As they gained popularity with artists, they were offered in smaller jars (8 and 4 oz.). Tubes were introduced in 1990.

2. Conservation
The conservation field has embraced Golden Heavy Body Acrylics (GHBA) for their quality, consistency, range of colors, versatility, and ease of use. Originally more commonly employed in objects conservation, they have increasingly been put to use in paintings conservation for inpainting, filling, and texturing.

The majority of use conforms to standard easel inpainting practices that rely on the employment of an isolating varnish layer prior to inpainting and final varnishes for even gloss and protection. In rare cases, GHBA are used without an isolating layer in instances where their reversibility in xylenes should effectively and safely separate them from the original, e.g., over water gilding or bole. Their opacity makes them useful when overpainting is necessary. The fluorescent and phosphorescent colors are not typically used in conservation.

Source

1. Physical
GHBA are composed of pigments in an acrylic emulsion binder.

At the time of writing, 101 colors were available (73 colors, 7 neutral grays, 3 primaries, 7 historical colors, and 11 custom colors). The following information is from Golden’s Product Information Sheet for Heavy Body Acrylics see website :

“The majority of Golden’s Heavy Body line is produced from single, unique pigments. About 30 of the colors are mixture colors. The mixture colors within the GOLDEN HB line of acrylics include Green Gold, Jenkins Green, Quinacridone Crimson, and Turquois (Phthalo), as well as…Neutral Grays, Historical Colors, Blended Colors, and Primaries.

Inorganic Pigments…are produced either with naturally mined pigments (sienna, umber, ochre) or with synthetically manufactured pigments, (iron oxide, carbon black, etc.). Pigments that are both mined and manufactured include the Cadmiums, Cobalts, and Titaniums.

Organic Pigments…are synthetically produced through complex carbon-containing chemistry involving various materials including petroleum, coal tar, and natural gas. Many of these pigments have their roots in the chemistry of the 1800s, although widespread production didn’t really begin until the 1930s. Even though they have only been available for several decades, organic pigments have demonstrated remarkable abilities to withstand the impact of light and weather..”

2. Origins and Manufacture
The GHBA are produced by:

Golden Artist Colors, Inc.

188 Bell Road

New Berlin, NY 13411

Phone (607) 847-6767

Website

The binder is manufactured by Rohm and Haas.

3. Manufacturers and vendors
The Golden Heavy Body Acrylics are widely available for purchase through art supply catalogs and stores.

Chemical and Physical Properties

1. Chemical classification
Acrylic Dispersion (Acrylic Emulsion)

Appearance is milky white or colored; there is a slight ammonia odor. pH: 8.5–9.2.

2. Chemical formula/structure
Poly (ethyl acrylate / methyl methacrylate) copolymer, [math]\ce{ (C5H8O2)n.(C5H8O2)m }[/math].

Figure 6 Chemical structure for Aquazol, Courtesy of Montserrat LeMense

3. Acrylic emulsion additives
Acrylic emulsion additives are described in the article “Conservation Concerns for Acrylic Emulsion Paints”. The list below is taken from the article:

Among additives to the acrylic emulsion:

• Initiators: most often persulfates, e.g., potassium persulfate.

• Chain transfer agents: e.g., dodecyl mercaptan.

• Buffers, to maintain a pH between 8 and 10, typically ammonia.

• Surfactants: typically added at 2–6% by weight. Some common surfactants are non-ionic (e.g., alkyl phenol ethoxylates) and anionics (e.g., sodium lauryl sulfate or dodecylbenzene sulfonate).

• Protective colloids: water soluble polymeric emulsifiers such as hydroxyethylcellulose and polyvinyl alcohol at 1 to 10% weight.

• Preservatives: to protect against the growth of microorganisms, generally at less than 1% weight. Commonly, methyl benzisothiazolinones, chloromethylisothiazolinones, barium metaborate, and formaldehyde donors, such as 1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride.

• Residual acrylic monomers are also present at 50 to 1,000 parts per million or so, resulting from incomplete polymerization.

Among additives in paint formulation:

• Wetting agents: similar to surfactants used during polymerization. Typical wetting agents include alkyl phenol ethoxylates, acetylenic diols, alkylaryl sulfonates, and sulfosuccinates.

• Dispersion agents, typically polyphosphates or polycarboxylates.

• Coalescing solvents: typical coalescents are ester alcohols such as TexanolⓇ (Eastman Chemical Co.), benzoate esters such as Velate. (Velsicol Chemical Co.), glycol ether esters, and n-methyl-2-pyrrolidone.

• Defoamers, typically mineral or silicone oils (e.g., polydimethylsiloxanes).

• Preservatives, as above.

• Thickeners and rheology modifiers: the most common group is that of cellulose derivatives, including hydroxyethylcellulose, methylcellulose, and carboxymethylcellulose. Also used, alkali-swellable polyacrylate emulsions and Polysaccharides, e.g., xanthan and guar gums. A newer group of rheology modifiers is that of hydrophobically modified ethoxylate urethanes (HEUR).

• Freeze/thaw stabilizers, 2–10% ethylene or propylene glycol.

According to product literature, the HB line of acrylics contains no additional flattening agents, opacifiers, or other solids that might interfere with the clarity of their pigments. This decision was made to allow their colors to retain their clearest and cleanest quality, especially when used in washes or glazes.

Product literature specifies formaldehyde as a preservative in the raw acrylic emulsion. The MSDS lists the presence of both ammonia and propylene glycol in all the acrylic formulations. Aluminum oxide and crystalline silica are listed in matte acrylics, gels, and mediums; semi-gloss lists only aluminum oxide.

4. Solubility
GHBA are ready to use from the jar. Water may be used to wet or thin them slightly without consequences; however, the color appears lighter after its addition and dries significantly darker, making color matching more difficult. Golden’s product literature cautions: the more water added to the acrylics, the greater the subsequent shrinking of the paint layer. Too much water will reduce the binding capability of acrylic paints and tends to flatten out their sheen.

The acrylics are not considered solvent miscible. Solvents will disrupt an acrylic film, especially a fresh one. Golden literature specifies that the acrylics are sensitive to the addition of solvents but suggests that if the addition of solvent is desired, the solvent should be first diluted with water to reduce the shock.

5. Tg
The glass transition temperature is near or below room temperature. The paint film softens at around 60ÅãC.

Preparation and Formulation

1. Typical preparation methods
Application methods for conservation purposes differ substantially from the methods described by Golden for general use by fine artists. Paint can be used directly from jars, but more commonly a palette is set up with the paints (and additional medium if desired). The palette will dry out at different rates depending on the climate and the amounts of paint. A water mister can be used to extend the working time of the paints or anything that slows water evaporation, such as a cover, a piece of MylarⓇ, or proximity with a damp sponge. Dried paint cannot be brought back into use and must be discarded. Paints are generally discarded at the end of a session. If a larger quantity has been mixed, it must be stored in an airtight jar, or the palette must be covered or sealed.

If acrylic inpainting is done as an underlayer that will have glazing layers or varnish applied over it, care must be taken not to pick up the acrylic film with solvents. When the acrylic inpainting has dried, a spray application of a resin in xylenes will not disturb it; the acrylic layer can be sealed in between layers of resin. Cautious brush applications of resins in mineral spirits are also possible but only to an extent; it will eventually swell or pick up the acrylic underlayer.

Application is typically by brush, but the acrylic paints and gels lend themselves well to other applications, such as palette knife or modeling tool when necessary to duplicate not just color but texture. Acrylic colors and gels can be applied as a fill material for lacunae.

2. Additives
The paints’ thickness and gloss can be altered with the addition of different media allowing for the duplication or approximation of a full range of oil paint techniques, including very heavy impasto, heavily ridged brushstrokes, palette knife marks, and other textures.

i. Gels and Mediums

The fluid media are thinner than the gels, are pourable, and can be used to thin the paints and alter gloss. The gels and mediums, without the paint, can be used to add texture to a flat fill before or after the color has been matched.

The gels are more viscous and do not pour. Gels are divided into different consistencies and sheens. The heaviest gels hold stiffer peaks but dry to a satin semi-transparent finish (waxy looking). In general, the mediums dry water-clear and glossy, as do the gels except for the heaviest and where specified in their description.

Extra Heavy Gel/molding paste has the heaviest body and holds the highest peaks; it exhibits less shrinkage than the other heavy gels and retains some transparency. Self-Leveling Gel is glossy and clear; it will do what its title suggests. It is useful for dot infilling and leveling out uneven fills and transitions; it can also increase the gloss of acrylic inpainting applied locally like a varnish.

Acrylic Flow Release is a concentrated surfactant; it contains no drier. It holds onto water and pulls moisture from the atmosphere. The addition of the flow release makes the paint sticky. It must be diluted according to instructions (10:1); it is of limited use for conservation purposes.

Retarder is described in product literature as “an additive used to increase the open (drying) time of acrylic paints. Useful for ‘wet in wet’ techniques and reducing skinning on the palette.” It is of limited use for conservation purposes.

ii. Airbrush Colors

Golden produces sets of opaque and transparent airbrush colors that are fully compatible with the other Golden acrylics. The airbrush acrylics are water thin and finely ground; they deliver an amazing amount of color in a very thin layer and are very useful in recreating missing glazes, for glazing broad areas of color, and in any application requiring a great deal of color and no bulk. Naturally, they work very well when airbrushed as well.

In addition, the Airbrush Medium can be used to thin the heavier acrylics without loss of color or film strength. An Airbrush Transparent Extender increases transparency and film hardness in the airbrush colors and is the recommended diluent for the airbrush colors.

3. Storage/shelf life
Store at room temperature. Avoid higher than normal temperatures. Do not allow paints to freeze. Once frozen, they cannot be reconstituted, which is a concern for delivery to colder climates. Replace caps tightly. Once dried out, they cannot be returned to use with either water or solvent.

GHBA have a reasonably long shelf life. Shelf life varies with individual pigments. Six to ten years is not an unreasonable expectation. Even with diligent storage, jars of acrylic will eventually get chunky or tough. A 4-oz jar of Golden Acrylic at Williamstown Conservation Center that is between 13 and 20 years old is still wet to the touch but exhibits undesirable texture and clumping; Mark Golden recalls a large container of cadmium red at use in an artist’s studio that was close to 25 years old.

Handling Characteristics

1. Appearance
GHBA are available in a full range of colors, both in jar and tube. The paint has a creamy texture similar to mayonnaise in weight and consistency. The heavy body of the paint allows for a fairly convincing recreation of missing impasto and heavier brushstrokes on damaged oil paintings, in some cases allowing “one step” fill and inpainting where smaller lacunae can be compensated with color and texture simultaneously.

They are described as thixotropic in the literature—vigorous stirring will return a slightly settled or seemingly thickened jar to its original creamy texture. The acrylic film remains flexible and feels slightly soft to the touch. Vigorous rubbing of the film will cause it to pill or crumble, especially when not completely dried. Because of its flexibility, it is difficult to scrape into the acrylic with a scalpel without rolling up or deforming the acrylic. The flexibility does allow for some manipulation of the surface before it dries completely, including burnishing prominent edges with a fingernail or similar device.

2. Application
Paint is ready to apply direct from the jar. A full range of media and gels are available to modify the texture, gloss, and thickness. Application is typically by brush but also using a palette knife, fingers, airbrush, etc.

3. Modifications for special applications and effects (“Tricks of the Trade”)
An especially dry atmosphere might require extra measures (like a spray mister) to keep paints from drying out too quickly. Many conservators have recommended the use of a wet palette with a lid to keep paints “open” long enough to finish larger inpainting projects. (Several conservators mentioned this tip.)

Use water to thin the paint, but adding too much makes correct color matching difficult, as the color lightens a great deal on the palette. Also, too much water makes a weaker film and slows drying time. The weaker film wrinkles easily and does not lend itself to further working in that area. A general recommendation is not to add water to the gels, as it increases shrinkage.

Gels are used for increasing the thickness and for manipulation of texture without affecting color. A caution: there will always be some shrinkage in the gels as they all contain water. There is less shrinkage in matte and high solid gels. Thicker gels have longer drying times. The shrinkage is documented by the manufacturer but is not a problem that conservators have found noticeable in use.

To achieve matte colors for inpainting—and especially effective on murals— mix Golden Acrylic titanium white with gouache. The acrylic is used as a medium and stabilizes the drastic color shift that gouache can display as it dries. The modified gouache colors have a matte surface reflectance (not the slightly plastic look one can get with acrylics) (Nina Roth Wells, personal communication, 2008).

A tip gleaned from the Golden website and tested by the author is to mix Quinacridone Crimson and Phthalo Green (blue shade) to make a deep black.

A few of the Golden acrylic colors are especially useful for modifying other colors by way of their high intensity and translucency. Among these, Green Gold and Quinacridone/Nickel Azo Gold are invaluable. No sane individual would reach for Green Gold off the shelf thinking it would be great for in-painting old paintings—it is a virulent pistachio color—but oddly enough, it is often just the right translucent undertone for many an aged oil color.

Aging Characteristics

1. Chemical process

• Acrylics are polymerized before the paint is manufactured, and no further chemical reactions are needed to form a film. The film is formed with the evaporation of water.

• Acrylic films can undergo chemical changes as they age that might cause chain breakage or additional cross-linking that would result in hardening, but these changes are very slow.

• Acrylic films become brittle at low temperatures, experiencing a drop in flexibility in a temperature range just above freezing (between 0 and 15Åã C). A brittle acrylic film would be susceptible to mechanical damage— cracking, breaking.

2. Resultant chemical and/or physical alterations
Yellowing is a negligible concern with acrylics; they essentially remain clear. Surfactant emulsifiers are exuded after film formation and remain after aging. Even after aging, acrylic films remain flexible. Aged acrylic films remain removable in xylenes.

From GOLDEN Acrylics product literature (see www.goldenpaints.com):

Pigment Selection and ASTM Standards

“Every color within the HB Line is approved for professional artist use according to ASTM Standards for Artist Materials. These standards regulate paint consistency and demand fineness and lightfastness of chosen pigments, use of 100% acrylic binder, freeze-thaw stability, and accuracy of labeling for pigments used. Evaluation by an approved toxicologist is required. Of the 101 HB colors, 94 within the line are considered excellent in lightfastness (the ability to withstand color change due to exposure to light). The remaining 7 are rated very good for lightfastness. GOLDEN does not use any colors within the HB line rated less than very good. Those colors rated as very good include the two Naphthols, Hansa Yellow Light, Permanent Green Light, Dioxazine Purple, Green Gold, and Primary Yellow. It should be noted that of the colors rated as excellent in lightfastness, the Cadmium colors are especially sensitive to the combination of light and moisture, so outdoor use of these colors should be avoided..”

3. Impact on appearance, solubility, and removability
GHBA exhibit good lightfastness and present no noticeable shift in color over time. There is no evidence to suggest that an aged acrylic film would present any increasing difficulty in removal over time. GHBP remain removable in xylenes. Freshly applied acrylics have a window of reversibility in water as well as mineral spirits. Reversibility in conservation practice depends as well upon the use of an isolating layer.

At the easel, recent extensive retouching has been removed from the surface of an isolating varnish with applications of a slow evaporating mineral spirits or by swelling with water followed by mineral spirits.

4. Attraction and retention of dirt and grime
The attraction and retention of dirt and grime is a concern with acrylics used as an artist’s material. The Smithsonian Museum Conservation Institute notes in the Care of Acrylic Paintings section:

“The surfaces of the soft acrylic films hold onto dust and dirt. The paint may even flow around the particles over time, so that they are incorporated into the film…Acrylic paintings attract and gather dirt easily. Acrylic emulsion paints used in the fine arts have glass-transition temperatures (Tg) near or below room temperature. This means that acrylic emulsion films will always be soft at room temperature...acrylic resins are nonconductors and tend to have electrostatic charges on their surface which attracts dirt..”

While there is reason for concern about the “cleanability” of fine art acrylic paintings, it is less of a concern with acrylics as they are used in conservation inpainting. The quantity tends to be smaller, thinner, and protected by a varnish—and its function, as a non-original addition, demands that it be distinct and removable and ultimately replaceable.

There has been no anecdotal information to suggest that the attraction of dirt or grime is a problem associated with GHBAs in their use as an inpainting medium. However, the possibility for attraction and retention of dirt is at its peak while the film is still wet or soft and before the film dries completely. With that in mind, additives of products such as Acrylic Flow Release (a concentrated surfactant) and Retarder should be used very cautiously or not at all to minimize the potential for trapping dust and particulates in the inpainting layer.

5. Theoretical lifetime
Frank N. Jones suggests that “While it is not known how long acrylic films will retain their physical qualities, evidence...suggests they will last hundreds if not thousands of years. Individual pigments are rated for lightfastness according to ASTM standards; Golden doesn’t use pigments with lower than “lightfastness II.”

Health and Safety

Since the GHBA use water as a diluent, they have a very low impact on one’s health. Used sensibly, they are among the safest choices available for inpainting. Health and safety concerns are primarily focused on the individual pigments. The release of small amounts of formaldehyde and ammonia during drying is worth noting. Individual jars are labeled in accordance with ASTM standards and carry warnings where needed. Hazardous component information for individual pigments can be found in the MSDS.

The same pigment is safer in its acrylic dispersion than as a loose particulate.

Disposal

Best practice focuses on allowing unused pigment to dry and disposing of it as a solid. Wipe excess paint from the brush prior to rinsing with water to minimize the amount of pigment released into the water system.

Montserrat LeMense

Submitted September 2008

Vendors

Conservation Support Systems
924 West Pedregosa Street
Santa Barbara, CA, 93101-4622
Phone: (800) 482-6299
Fax: (805) 682-2064
Website
E-mail: css@silcom.com

TALAS
568 Broadway
New York, NY 10012
Phone: (212) 219-0770
Fax: (212) 219-0735
Website
E-mail: info@talasonline.com

Daler-Rowney
2 Corporate Dr.
Cranbury, NJ 08512-9584
Website
Phone: (609) 655-5252
Fax: (609) 655-5852

DaVinci Paint Company
11 Goodyear St.
Irvine, CA 92618
Website
Phone: (800) 553-8755
Fax: (949) 859-4766
E-mail: dvp@davincipaints.com

Holbein
Website

H. Schmincke and Co.
GmbH & Co. KG
Otto-Hahn Str. 2 D40699
Erkath, Germany
Website

Kremer Pigments
247 West 29th Street
New York, NY 10001
(212) 219-2394
www.kremerpigments.com

Lefranc et Bourgeois
357 Cottage Street
P.O. Box 2484
Springfield, MA
Website

Maimeri
Website
E-mail: maimeri.info@maimerispa.it

M. Graham and Company
P.O. Box 215
West Linn, OR 97065-0215
Website
Phone/Fax: (503) 656-6761

Reeves, Oasis Art and Craft Products Ltd.
Goldthorn Rd.
Kidderminster, Worcestershire, DY 117 JN, UK
Website
Phone: +44 0 1562-744522
Fax: +44 0 1562-823181
E-mail: enquiry@reeves-art.co.uk

Royal-Talens Company
P.O. Box 4
7300 AA Apeldom, Netherlands
Website
E-mail: info@talens.com

Savoir-Faire
40 Leyeroni Court
Novato, CA 94949
Website
Phone: (415) 884-8090
E-mail: Productinfo@savoirfaire.com

Winsor and Newton
In the United States, 11 Constitution Ave., Piscataway, NJ 08854
Website
Phone: (800) 445-4278

Lefranc & Bourgeois
357 Cottage Street
P.O. Box 2484
Springfield, MA

Additional Resources Consulted

BASF website

Booth, S. D. and C. Metzger. 1984. Unpublished manuscript, AIC Paintings Specialty Group, AIC Annual Meeting.

Brevig, L. 2004. Personal communication.

CAMEO Website

Fisher, E. 2005.Egg tempera retouching conference: UKIC Paintings Section. In Conservation news (United Kingdom Institute for Conservation of Historic and Artistic Works) no. 97 (July), 35–36.

Gamblin Conservation Colors website

Gritt, S. 2004. Personal communication.

Kempski, M. 2010. The art of tempera retouching. In Mixing and matching: Approaches to retouching paintings, eds. R. Ellison, P. Smithen, and R. Turnbull. London: Archetype.

Gritt, S. 2004. Massing, A. 2010. The history of egg tempera as a retouching medium. In Mixing and matching: Approaches to retouching paintings, eds. R. Ellison, P. Smithen, and R.Turnbull. London: Archetype.

Gritt, S. 2004. Phenix, A. 2010. The composition and chemistry of eggs and egg tempera. In Mixing and matching: Approaches to retouching paintings, eds. R. Ellison, P. Smithen, and R.Turnbull. London: Archetype.

Lefranc & Bourgeois. Undated product information sheet.

Pomerantz, L. 1976. Inpainting with Bocour paints. In Inpainting: A panel presentation, presented at the American Institute for Conservation of Historic and Artistic Works fourth annual meeting, 143. Dearborn, MI.

Samet, W., compiler. 1998. Painting conservation catalog, Vol. 1: Varnishes and surface coatings. Washington, DC: Paintings Specialty Group of the American Institute for Conservation of Historic and Artistic Works.

Simmons, M. 2000. The good egg. New York: Houghton Mifflin.

Stoner, J. H. 2000. Hell vs. Ruhemann: The impact of two German conservators on U.S. painting conservation theory. In 2000 AIC Paintings Specialty Group Postprints, Philadelphia, Pennsylvania, June 8–13, 2000.

Tate AXA Modern Paints Research Project (TAAMPP): 2006–2009. Available here

Endnotes

^{The Tg for PEOX was reported by Chiu et al., and subsequently referenced by others, as 55oC. The present manufacturer’s technical data give a Tg value for Aquazol of 69–71oC [~154 -159oF]. The manufacturer’s information graphs indicate that at 50% RH and 74oF, Aquazol achieves an equilibrium moisture content of ~5% by weight and that the addition of ~5% water will drop the Tg of Aquazol from ~70oC into the ~55oC range. However, they suggest that the earlier reported value may also be related to imposed laboratory conditions that prevented the samples from achieving normal, post-polymerization equilibrium.}

^{Chemical Abstracts Service (a division of the American Chemical Society) Registry Number for the monomer.}

^{Polymer Chemistry Innovations Incorporated, 4231 South Fremont Avenue, Tucson, Arizona 85714; Phone (520) 746-8446, Fax (520) 746-8876.}

^{Young’s Modulus is also referred to as the Modulus of Elasticity in Tension. This is a measure of a material’s strength and elasticity; specifically, the deformation produced in the material by a given amount of applied force. The ratio of stress force to strain elongation (i.e., the amount that a particular material stretches when it is pulled on) can be represented as the slope of a graphed line. The percentage of the material’s original length that it stretches before breaking is a useful measure of its comparative brittleness.}

^{The observed drop from an initial size of about 300,000 daltons to around 50,000 daltons in the light aged samples of Aquazol 500 could indicate the occurrence of chain scission at a frequency of 1:600 monomer units.}

^{No positive increases were measured in the “b” coordinate value of the L*a*b* notation used..}

^{Superfund Amendments and Reauthorization Act of 1986, also known as the Emergency Planning and Community Right-to-Know Act (EPCRA), pertaining to any hazardous substances for which a facility must maintain a MSDS under the OSHA Hazard Communication Standard.}

^{Information on formulas comes from “Diluents, Fillers, Binders, and Coatings” by James Bernstein, excerpted from James Bernstein and Debra Evans’ Mastering Inpainting Workshop Manual (June 2010 edition, San Francisco, California). This is a combination of original and compiled information provided as an education resource to participants of Mastering Inpainting or Mastering Fills workshops.}

^{Safflower oil is the more common oil (as opposed to walnut) added to commercially made oils. The Winsor and Newton website notes that “most of our whites are milled with safflower oil.” Of course, walnut is the historic oil used for light colors, but I think it is more expensive and has been replaced by safflower in modern day manufacturing.}

^{Pure ethanol will not dissolve PVAc; some water is also required. However, since ethanol is hygroscopic, most opened containers of ethanol will contain enough water to dissolve PVAc.}

^{Physical and chemical data (average molecular weight, solubility, and Tg) for Golden PVA paints have been provided by Golden Artist Colors, Inc. and are published in a technical leaflet available on the manufacturer’s website.}