VI. Wax as a Surface Coating

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Painting Conservation Catalog
VI. WAX AS A SURFACE COATING


Author: Carole Abercauph
Date: Submitted October, 1996
Compiler: Wendy Samet

TABLE OF CONTENTS:
A. HISTORICAL BACKGROUND
B. CLASSIFICATIONS WITH CHEMICAL AND PHYSICAL PROPERTIES
C. FORMULATIONS
D. SHELF LIFE
E. WORKING CHARACTERISTICS AND PRACTICAL PROPERTIES
F. AGING CHARACTERISTICS
G. HEALTH AND SAFETY

A. HISTORICAL BACKGROUND

1. Industrial Use

Wax is used extensively in coatings and polishes.

2. Artistic Use

Wax has been used for at least two and a half millennia as a paint medium, surface coating, and sculpture material. There is documentary evidence of use by Reynolds, Delacroix, and Gauguin (Mayer 1996, 5).

3. Conservation Use

Since the 1930s, mixed and simple formulations have been used: as surface coatings on paintings that could not be varnished with solvent varnish solutions; as protective coatings (from dust and dirt) over spirit varnishes because of ease of removal with mild solvents; as local applications to even gloss of other varnishes; as additives to other varnishes to control (usually reduce) reflectance; as consolidants; as lining adhesives; as fill material (especially good for very shallow losses that are difficult to fill with other fill materials)

B. CLASSIFICATIONS WITH CHEMICAL AND PHYSICAL PROPERTIES

The term “wax” popularly refers to a chemically heterogenous group of materials that resemble natural waxes such as beeswax in being low-melting translucent solids with a waxy feel. Chemically, waxes are generally materials containing long-chain hydrocarbons, acids, alcohols, esters, or mixtures of these (Mills and White 1987, 49).

1. Natural Waxes (a short list, tables list others):

a) Animal Origin
(1) BEESWAX
A secretion of organs situated on the underside of the abdomen of working (neuter) bees for use in forming the cells of the honeycomb (Gettens and Stout 1966, 5), that is melted to form yellow cakes, bleached and melted to form white cakes, or sold unprocessed; melts in range of 63–66°C; readily available from many processors and vendors; soluble in carbon tetrachloride, ether, turpentine; slightly soluble in petroleum distillates, ethanol, acetone, Cellosolve® acetate; insoluble in MEK (all solubilities extrapolated from Gettens and Stout 1966; Davidsohn and Milwidsky 1968).
b) Vegetable Origin
(1) CARNAUBA WAX
An exudate on the leaves of the Brazilian palm, Corypha cerifera (the carnauba tree) that is processed by melting and bleaching and forms a hard, yellowish, brittle material of exceptionally high melting point (83–86°C), and produces high gloss shine when buffed (Gettens and Stout 1966, 7). It is readily available from many processors and vendors; soluble in turpentine; slightly soluble in petroleum distillates, carbon tetrachloride, ether, ethanol, chloroform, and acetone; and insoluble in MEK.

2. Mineral Waxes Obtained by Petroleum Distillation

a) Paraffin Waxes
A mixture of mostly solid straight-chain saturated hydrocarbons with the general formula CnH2n+2 (The Merck Index 1952, 719); various available formulations melt in range of 37–66°C, the higher the molecular weight, the higher the melting point. Molecular weights may range from ca. 350 to ca. 420; sold as molded blocks or flakes, color should be translucent or milky white. This wax is readily available from many producers and vendors. It is soluble in benzol, ether, chloroform, carbon disulfide, carbon tetrachloride, turpentine, petroleum distillates, and fixed oils; partially soluble in acetone, diacetone alcohol; and insoluble in MEK, ethanol, and isopropanol (Davidsohn and Milwidsky 1968).
b) Microcrystalline Waxes
Derived from petroleum distillation fractions that are heavier than those for paraffin waxes, microcrystalline waxes usually have branched saturated hydrocarbon chains. The various available formulations melt in the range of 60–94°C, with proportionately higher molecular weights (MW may range from ca. 500 to ca. 800). These waxes are generally tougher, more flexible, with lower luster than paraffin waxes. They are sold as molded blocks or flakes, with the color varying from brown to white. Microcrystalline waxes are readily available from many producers and vendors; solubilities as for paraffin waxes (Davidsohn and Milwidsky 1968).
c) Mined Waxes
Earth waxes, today indistinguishable from microcrystalline waxes - ozokerite, originally as it came from the mine; ceresin, refined ozokerite (Davidsohn and Milwidsky 1968).

C. FORMULATIONS

1. Mixtures for Coatings to Be Applied by Brush or Rag

a) Rosen Formula
beeswax (1 part), carnauba (2 parts), ceresin (2 parts), combined with enough naphtha to make soft paste; ingredients are heated to insure uniform mixture (Rosen 1934, 114–15).
b) Massey Formulas (Massey 1967, 161–4)
(1) beeswax (1 part), turpentine or mineral spirits (3 parts), heat in double boiler until wax goes into solution, stir occasionally as solution cools to a very soft paste.
(2) white ceresin wax (1 part), toluene (4 parts); place ingredients in capped bottle and allow to dissolve into very soft paste.
(3) carnauba wax (2 parts), ceresin (2 parts), beeswax (1 part), turpentine (15 parts); melt ingredients in wax pot until carnauba has dissolved into solution; allow liquid to cool until can be poured into can or bottle.
(4) beeswax emulsion (for use over paints or varnish that might be softened with wax-in-solvent mixtures): beeswax (1 part), water (8 parts), ammonium carbonate (1 part); combine beeswax and water and melt in pan at least three times the volume of ingredients as solution foams; stir in ammonium carbonate, a little at a time; if foam threatens overflow, remove from heat and continue stirring until foam subsides; about half the water volume is lost during manufacture and it may be replaced later with cold water. (Note: all natural waxes may be saponified with alkalis; mineral waxes do not saponify with alkalis).
c) Taubes Formula
Beeswax (1 ounce) should be dissolved in mineral spirits (3 ounces) until a “limpid salve” results (Taubes 1944).

2. Spray Solutions

a) Reported by Morton C. Bradley, Jr.
1 part coating wax (unidentified) is heated with 10 parts carbon tetrachloride (“Although it is toxic, carbon tetrachloride is used because it is not flammable” until wax is completely dissolved [[[#ref1|Bradley 1950]]].) (This recipe is offered as a warning about the kinds of things we used to do to ourselves and perhaps still do with a different set of ingredients.)

D. SHELF LIFE

1. Wax Blocks or Flakes

Will store indefinitely without change.

2. Mixed Coating Waxes

Will store indefinitely in sealed containers; storage precautions would be based upon the type of solvent in the mixture.

E. WORKING CHARACTERISTICS AND PRACTICAL PROPERTIES

1. Appearance

Wax varnishes have a low luster sheen that can be somewhat controlled by buffing the surface and by the choice of wax used (i.e., generally, the harder the wax, the glossier the sheen; carnauba wax is the hardest natural wax and may be buffed to the highest shine of any of the natural waxes).

2. Brushing or Rubbing

Wax is most often rubbed or wiped onto the painting surface as a very thin layer. Liquid formulations may also be brushed onto the surface. They become opaque when dry. The drying time varies with ambient conditions but is usually of short duration. The surface is buffed with a soft cloth to attain the desired sheen.

3. Usual Applications

Most authors recommend the use of wax as a coating on top of a resin film to reduce the gloss of the surface overall or to protect the varnish from dirt. The wax may be removed and replaced if necessary without disturbing the underlying varnish. Wax may be used as a final coating for a paint film that has a rough conformation that was unintended and could not be eliminated by other means. The low luster appearance of the wax would eliminate the highlights on the elevations (Bradley 1950). Local application may be made with a finger or cloth to matte down overly glossy areas of a varnished painting (proprietary wax mixtures such as Renaissance® Wax may be used for this purpose).

4. Extent of Use

An unscientific survey of painting conservators indicates that wax alone is little used in the field as a separate final surface coating although it continues to be used as a fill material, consolidant, and lining adhesive. It is, however, commonly used as an additive to the final spray coats of many natural and synthetic resins to mat them down or create a more even surface gloss (See individual resin entries under “Additives”). Those of us who occasionally do use waxes alone as a final coating often have a jar of Renaissance® Wax, a proprietary formulation of mixed microcrystalline waxes, that we have used on occasion to matte down or even out already applied varnishes. We all (the individuals in the small unscientific survey) seem to use this product because it is easy to use and performs the limited use task well.

F. AGING CHARACTERISTICS

Wax is perhaps the only surface coating that has passed the test of time.

1. Chemical Process

“Wax is very resistant to acids. With lye it forms an emulsion. It does not oxidize, as do fatty oils, and it does not turn yellow and loose in body. It has been found unchanged in very ancient remnants of paintings” (Doerner 1949, 141). Of all surface coatings, it is the least permeable to water, water vapor, and gases (Rosen 1934).

2. Physical Deterioration

Wax coatings scratch and mar easily. Because of relative softness or plasticity that may occur at high ambient temperatures they may retain dirt.

3. Solubility and Removability

Waxes of all types are very stable materials that remain soluble in their original diluents. Removal from the surface of another varnish film should not be problematical, provided that the resin varnish was not or no longer is soluble in petroleum distillates.

4. Theoretical Lifetime

Wax has an indefinite theoretical lifetime. Shrinkage and brittleness of artifacts composed of beeswax has been reported (Clydesdale 1994) but such problems have not been reported for wax varnishes.

G. HEALTH AND SAFETY

(extracted from MSDS sheets)

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 solvent admixtures to waxes. All waxes are flammable and must be kept away from furnaces, flames, etc.



Table 1. Properties of Commercial Waxes
Waxes Characteristics Color Melting point, °C Penetration at 25°C Flash point, °C Specific gravity at 25°C Acid number Ester number Saponification number Iodine number Refractive Index Unsaponified matter, % Source
bayberry waxlike fat, hard, brittle grayish green to white 38–49 4–6 243 0.977–0.982 5–24 205–215 210–239 2–10 1.4360 0.3–0.5 berry
beeswax amorphous, wax, slightly tacky deep brown to light taffy white 62–65 15–20 242 0.950–0.960 17–24 72–79 89–103 8–11 1.440–1.445 52–55 insect
candelia hard, brittle, slightly tacky, lustrous brownish to light yellow 68.5–72.5 1.5–5 240 5.982–0.993 12–22 31–43 43–65 19–44 1.4600 65–75 shrub
carnauba very hard, brittle not tacky, lustrous pale yellow to greenish brown 83.0–86 1–3 298 0.996–0.998 2–10 76–78 78–88 7–14 1.4540 50–55 palm
ceresia dense, crystalline hard, dry white to tan 53.3–85 7–14 204 0.880–0.935 2 maximum 1.425–1.435 100 petroleum
Japan resembles hard fat pale cream 46.5–51.5 6–20 196 0.975–0.984 6–30 194–200 200–225 4–15 1.4550 2–4 berry
microcrystalline sticky, plastic to hard, dry, amorphous to crystalline white, yellow amber, brown, black 60–96.5 2–80 260 0.915–0.935 1.424–1.452 100 petroleum
1.437–1.440
montan, German American hard, brittle dry, lustrous blackish, brown 83–89 1–5 293 1 .020–1.030 31–55 55–70 87–125 14–18 1.467 35–40 lignite
40–55 55–70 95–125
ourlcury very hard brittle dry, lustrous light to dark brown 82.5–84.5 1.5–2.5 276 0.970–1.050 8–18 72–87 80–105 6–8 1.4478 50–55 palm
oxidized microcrystalline hard, crystalline yellow, orange-brown, brown 82.5–93 4–8 260 0.915–0.935 15–50 12–40 27–90 1.430 50–70 petroleum
ozokerite fairly hard, fibrous structure, tough dark brown, white, yellow 63–93 4–25 204 0.950–0.960 1.4400 100 petroleum
paraffins soft to hard solid, coarse fibrous crystals, oily to dry white 44.5–74 6–40 193 0.880–0.920 1.424–1.430 100 petroleum
rice bran hard, dry, slightly crystalline tan to light brown 76–82 2–5 271 0.990–0.998 5–15 65–95 70–105 10 maximum 1.455 39–57 seed

From Encyclopedia of polymer science and engineering, eds., Vol. 17, 1989, 792–3. Reproduced by permission.




Table 2. Characteristics of Animal Waxes
Beeswax Chinese Shellac Wool fat Walrat
Insect Wax Wax Crude Refined
Specific Gravity 15/15°C 0.955–0.970 0.952–0.975 0.970–0.980
Melting Point °C 60–64 80–83 75–80 32–38 40–42 42–46
Acid Value 18–23 10–15 12.5–16 14–15.5 0.5–4.5
Saponification Value 88–103 90–96 120–1301 78–125 98–127 122–136
Ester Value 70–80 75–81 108–114
Iodine Value 12–21 1–2 1.25 28–30 19–22
Unsaponifiable Matter% 52–58 52–56 72–76 40–50 35–45 49–56

1Commercial shellac waxes with a saponification value not lower than 80 are still acceptable.




Table 3. Characteristics of Common Vegetable Waxes
Carnauba Wax Candelilla Wax Ouricuri Wax Esparto Wax Sugar-Cane Wax Cotton Wax
Specific Gravity 15°C 0.990–0.999 0.950–0.993 0.970 0.986 0.9612–0.989 0.959
Melting Point °C 84–91 64–70 83–85 73 55–76 refined 82° 68–71
Refractive Index °C 1.472/40 1.452/80
Acid Value 2–4 12–20 12.0–16.0 28 4–12 32
Saponification Value 79–87 60–65 86–92 61.6 40–57 70.6
Ester Value 76 32–82 73–92.5 33.6 28–40 38.6
Iodine Value 8–14 12–21 8.6–12.8 8.2 12.4–16.2 24.5
Unsaponifiable Matter% 50–55 65–77 48.5 more than 50 69
Acetyl Value 55–122 55–95 73.1
Ash% 1.0

Data for Tables 2–3 from Davidsohn and Milwidsky, Polishes, 1968. Reproduced with permission of the publisher.




Table 4. Mined Waxes
Properties Quaker State Barnsdall Micro Wax Syncera Wax Special Wax Socony 2300 Be Square Special
Melting Point °F 145–146 160–165 155–160 155 160–185
Specific Gravity at 60°F 0.900–0.920 0.920–0.940 0.912 0.92–0.94
Specific Gravity at 210°F 0.780–0.800 0.800–0.820
Viscosity at 210–F(Saybolt) 75–85 75–100 51 65 75–100
Flash Point °F 500 min. 500 min. 425 495 500
Fire Point °F 575 min. 575 min. 550 575
Saponification No. 0.05–0.10 <2 0 <2
Acid No. 0.1 maximum 0.1–0.2 0 0.1–0.2
Iodine No. 1.5
Color white to amber white to amber yellow yellow-brown white-black
Penetration No. (ASTM) (Petroleum Method at 77°F; 100 g wt.) 5–10 20–2 5–20




Table 5. U.S. Microcrystalline Waxes
Name of Wax Melting Point ASTM D-127–30 Penetration 100G/77°/5 sec. Color NPA Acid No. Saponification Value Type
Fortex 190–200 3–5 2–1/2–3–1/2 0.0 0.0 Microcystalline hard & plastic
Mekon
B-20 190–195 3–5 brown-black Microcrystalline hard & brittle
A-20 190–195 3–5 amber-6 max.
Y-20 190–195 3–5 yellow 3–3–1/2 0.0 0.0
Warco Wax 180 180–185 4–7 white 0.0 0.0 Microcrystalline hard & brittle
Warco Wax 150 145–150 20–25 brown-yellow 0.0 0.0 Microcrystalline plastic
Warcosine 145–150 15–20 white 0.0 0.0 Microcrystalline plastic
Crown Waxes
200 190–195 10 max. brown 0.0 0.9 Micrycrystalline hard & plastic
500 190–195 10 max. 2–2–1/2 0.0 0.0
700 190–195 5 max. 2–2–1/2 0.0 0.0
1,035 195–200 2 max. 2–2–1/2 0.0 0.0

Data for Tables 4–5 from Davidsohn and Milwidsky, Polishes, 1968. Reproduced with permission of the publisher.

REFERENCES

Bradley, M.C., Jr. 1950. The Treatment of pictures. Cambridge, Mass.: Art Technology.
Clydesdale, A. 1994. Beeswax: A survey of the literature on its properties and behavior. SSCR Journal 5(2): 9–12.
Conservation Materials Ltd. [n.d.] Wax (entries). In Catalog [Conservation Materials, now no longer in business, also supplied the MSDS for the waxes they carry.]
Davidsohn, A. and B.M. Milwidsky. 1968. Polishes. Cleveland, Ohio: C.R.C. Press.
Doerner, M. 1949 [originally published in German, 1922, first American translation, 1934]. The Materials of the artist and their use in painting with notes on the techniques of the old masters. Revised ed. E. Neuhaus, transl. New York: Harcourt, Brace and Company.
Gettens, R.J. and G.L. Stout. 1966. Painting materials: A short encyclopedia. New York: Dover Publications.
Heslip, M. [n.d.] Conversations about days of yore [Thank you Michael!].
Mark, H.F. and J.I. Kroschwitz. 1989. Encyclopedia of polymer science and engineering, Volume 17. New York: Wiley:792–93
Massey, R. 1967. Formulas for painters. New York: Watson-Guptill Publications.
Mayer, L. 1997. Traditional varnish materials. In Painting Conservation Catalog, Volume 1: Varnishes and surface coatings [Section II herein].
Mayer, R. 1970. The Artist's handbook of materials and techniques. New York: Viking Press.
Merck Company. 1952. The Merck Index of Chemicals and Drugs. Rahway, N.J.: Merck Company.
Mills, J.S. and R. White. 1987. The Organic chemistry of museum objects. Sevenoaks: Butterworths.
Payne, H.F. 1961. Organic coating technology. Vol. 1. Oils, resins, varnishes and polymers. New York: JohnWiley & Sons.
Rosen, D. 1934. A Wax formula. Technical studies in the Field of Fine Arts 3:114–5.
Stout, G.L. 1975. The Care of paintings. New York: Dover Publications.
Taubes, F. 1944. Studio secrets. New York: Watson-Guptill Publications.
Wehlte, K. 1975. The Materials and techniques of painting. 2d ed. New York: Van Nostrand Reinhold.



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