PMG Cased Photographs
Photographic Materials Conservation Catalog
Cased photographs: Including Daguerreotypes, Ambrotypes (Collodion Positives), and Tintypes
The chapter reviews component construction and care of cased photographs.
Date: September 1998
Contributors for WIKI version:
Compiler for printed chapter #2 (1998): John P. McElhone
Contributors for printed chapter #2 (1998): Gary Albright, M. Susan Barger, Valerie Baas, Lee Ann Daffner, Deborah Derby, Tom Edmondson, Monique Fischer, Chris Foster, Lynne Gilliland, Marion L. Hunter, Jr., Wayne King, Barb Lemmen, Mark H. McCormick-Goodhart, Angela Moor, Ian Moor, Peter Mustardo, Debbie Hess Norris, Nancy Reinhold, Andrew Robb, Elena Bulat, and Annabelle Chabauty.
Chapter #2 edition copyright (1998): The Photographic Materials Conservation Catalog is a publication of the American Institute for Conservation of Historic and Artistic Works. The Photographic Materials Conservation Catalog is published as a convenience for the members of the Photographic Materials Group. Publication does not endorse nor recommend any treatments, methods, or techniques described within the chapter.
TABLE OF CONTENTS:
2.2 Cases and Other Housing Formats
2.3 Daguerreotype Plates
2.4 Ambrotype Plates
2.5 Tintype Plates
Purpose of information in this entry
- To physically and chemically stabilize the object.
- To reintegrate the original case or package to best represent the original appearance of the object.
- To provide preventive care during storage.
- To consider traditional and current methods of removing tarnish from daguerreotype plates and other cosmetic treatments.
Cases and Other Housing Formats
22.214.171.124 Hinged Case (commonly found on American and British plates)
The case is a multiple component structure which works to protect the photographic plate from physical damage and from the environment. Original cases also provide an appropriate aesthetic setting for the image. The plate is contained in a package consisting of several layers. The plate, together with a metal mat and a cover glass, may be bound together with an adhered paper strip. The metal mat is sheet brass. It is stamped (or molded) with a decorative pattern and may be etched to give an overall surface texture. Mats may be gilded and are usually coated with a colored varnish (shellac tinted with a variety of natural colorants). A mat provides a decorative setting for the image and keeps the cover glass, if present, away from the image surface. Note that while it may be possible to date brass mats of the 1840-1865 period on the basis of their thickness and decorative finish, this does not necessarily relate to the image date since mats may have been interchanged. The preserver is a flexible strip of a copper alloy foil that folds around the glass/mat/plate package. The use of preservers on daguerreotypes began later in the 1840s, possibly 1847. They are usually stamped with a decorative pattern and serve a decorative purpose as well as protecting the paper binding, if this is present. Most importantly, the preserver preserves the daguerreotype image from tarnishing by preventing air ingress; it does this by pressing the package components together, most effectively when the package is pressed into the case. (See notes on the retainer also.) Occasionally, no preserver was used; in such instances, the sealing tape is adhered to the edge of the cover glass but does not extend onto the front surface. This is more often seen in British cases than in American ones, although early American cases often lack the preserver. The case is composed of two halves, a cover and a tray, that are hinged together. It may be covered with embossed or plain leather, molded paper or papier-mâché, textile (including velvet), lacquer/mother-of-pearl, or even more exotic materials. Leather-covered cases frequently show gilt tooling. The covering materials are adhered to the wooden base. Hinges may be of brass, attached to the trays with small brass nails. The hinge can also be created by extensions of the leather, textile or paper that covers the tray. When the hinge is contiguous with the covering material, there may also be an interior hinge to reinforce the exterior one. The tray has a velvet-covered cardboard retainer around its perimeter. The retainer presses the components of the package together inside the cavity of the tray and acts to seal the package interior from air infiltration. The case cover holds a cushion -- a convex cotton pad covered with velvet or satin. The cushion reduces the volume of potentially harmful air inside the closed case and provides some protection to the cover glass from breakage. The case often has one or two brass hook-and-eyelet clasps attached on the exterior right edge to secure it closed. The "Union case" is an American variation made with an early thermoplastic material composed of shellac, cellulosic fibres and pigments; this material was molded to make cases with detailed decorative motifs and representational scenes. Introduced in 1853, they usually have brass hinges and often have an integrated spring clasp rather than hook-and eyelet clasps. Occasionally, two or more photographs are contained in the same case. Not shown in the illustration (see next page), but frequently encountered in both daguerreotype and ambrotype packages, is the paper sealing tape adhered to the perimeter of these package elements which binds them together. Ambrotype cases may differ somewhat from daguerreotype cases. If the ambrotype has not been painted with a pigmented lacquer on the plate verso, a dark-colored paper, textile or glass layer will be included behind the image plate. The cover glass may not be present in ambrotypes where the collodion image layer faces the interior (this having been done to correct lateral reversal of the image). In such instances, the metal mat and the preserver are adjacent to each another.
Illustration: T. Pritchard
126.96.36.199 Passe-partout (European daguerreotypes, stereographs)
Daguerreotypes originating elsewhere than Britain and North America, as well as stereo-daguerreotypes, may be found packaged in this format. It consists of glass and paper elements with a cardboard backing. (See illustration below.) Passe-partout with paper mat: The mat is usually a heavy wove paper with drawn or printed decoration. The mat aperture is most often square or octagonal in shape. The cover glass is fixed over the paper mat with a colored paper binding tape adhered around the package perimeter. (Some early American daguerreotypes, especially mourning portraits, incorporate gold-painted paper mats.)
Illustration: T. Pritchard
Passe-partout with reverse-painted cover glass: The earliest examples of this format are quite simple. Later examples include simple decorative lines, elaborate transfer designs or elaborate geometric patterns and decorative painting techniques (for example, tortoise shell patterns). When examined on the verso surface, these reverse-painted glass plates often have a matte-texture paint layer applied over the decorative paint, possibly as a protective layer. Both types of passe-partout housings were eventually made commercially and could be purchased by the daguerreotypist. An open flap on the cardboard backing allowed the processed image plate to be placed in position under the aperture and fixed with several strips of adhered paper. The flap was then closed with more paper strips or with a paper sheet adhered over the whole package verso. Paper binding tape was adhered to the package periphery. It may be colored or decorated to aesthetically integrate with the rest of the package design. (For instance, coated paper or marbled paper may be used as binding tape.) The cardboard backing of the package is usually covered with a colored paper sheet, and inscriptions and labels are often found here.
American, British and European daguerreotypes, ambrotypes and tintypes may be found in wooden, thermoplastic composite or papier-mâché frames. The plates will be contained in the same kind of plate packages that would otherwise be presented in a case or passe-partout. The frame may either be original or a later addition.
188.8.131.52 Paper Housings
Small tintypes are sometimes mounted inside paper mats whose dimensions approximate the carte-de-visite format. These mats consist of a backing sheet onto which the plate is directly adhered, covered by an aperture overmat. The overmats were often decorated with embossed or printed motifs and with the photographer's identification. The top sheet is often adhered to the bottom sheet and to the concealed perimeter of the plate surface.
The leather, cloth or paper case hinges are often the weakest component in a hinged case. It is not unusual to encounter cases with the hinges either partially torn or with the trays completely detached from one another. Sometimes the cover will be missing. Hinges will often have been reinforced or replaced, often with poor-quality or inappropriate materials.
184.108.40.206 Leather and Paper Case Coverings
Case coverings are frequently torn or have lost small sections; separation from the wooden base may have occurred. The exterior surface, particularly the raised portions of any pressed pattern, may be abraded, resulting in the loss of color and finish. Leather, particularly leather hinges, may be brittle. Gilt tooled or bronze painted decoration on the case exterior and interior may be soiled or abraded. A variety of surface coatings, especially waxes and oils, may have accumulated during a long history of cosmetic treatments.
220.127.116.11 Paper Tape and Mats
While goldbeater's skin was occasionally used to seal the edge of plate packages, sealing tape was most often made from strips of paper that had a thin layer of water-soluble adhesive applied to one side. Early daguerreotypists used strips of writing paper, but as the craft became an industry, rolls of paper tape prepared specifically for this purpose became available for purchase. The preservation state of the sealing tape depends on the quality of the paper used, the type of adhesive and the amount of mechanical wear that the seal has received in handling. Tapes might have been split open to examine the package interior and then inexpertly resealed. Plates inside passe-partout packages were fixed with strips of gummed paper tape adhered to the verso surface of the paper mat or reverse-painted cover glass; these attachments are often found to have desiccated and released. Plates in this housing format frequently slip inside the package. The paper mats of the passe-partout packages may be light damaged or may show adhesive stains. These packages may have been opened once or several times over the years to examine the plate; they will show evidence of more or less expert resealing. Several layers of backing paper, some of them fragmentary, may have accumulated on the package. The paper mats applied to small tintypes may show staining and mechanical damage. Adhesives holding the plate to the paper may have desiccated and failed, leaving the tintype plate loose between the paper layers. The adhesives used may have initiated rusting of the iron support.
Glass used for both glazing and support materials for cased photographic images was usually commercially available pane glass. There were some companies that sold "photographic" glass destined for use as supports for photographic plates. This glass was free of physical flaws and was relatively colorless, but did not have superior durability or corrosion resistance. All glass is subject to physical breakage. Broken cover glass on cased photographs may cause immediate physical damage to the image underneath. In addition, it may lead to chemical deterioration of the image in the localized area under the breakage by allowing the direct ingress of air; this is particularly common with daguerreotypes with cracked cover glasses. Some glass formulations are chemically unstable due to a high flux content, especially those with a high ratio of sodium flux in proportion to the alkaline earth flux (calcium and magnesium oxide). Note that glass with a high sodium content produces a yellow-orange fluorescence under UV illumination, whereas glass with a higher alkaline earth content tends to produce orange-magenta fluorescence. Glass corrosion is caused by inherent instability linked to unfavorable environmental conditions. Glass corrosion, leading to the accumulation of alkaline materials and silicates on the surface of the glass, is a major cause of deterioration in cased photographs. Unfortunately, the design of the cased photograph package encourages the type of corrosion in cover glass called "static weathering." In this process, the inner surface of the cover glass is exposed to a small enclosed air volume; this air is subject to transient periods of high or cycling relative humidity. The glass used in photographic packages should be checked regularly for signs of weathering corrosion. It may be easier to detect corrosion films by examining the glass by specular reflection. Look for:
- early signs -- a faint surface haze or clouding;
- more advanced states of "weeping" glass, including the presence of tiny droplets that lend a "greasy" or "soapy" feel to the surface; these are primarily amorphous sodium silicates (water glass) and have a high pH -- in the range of 10-14 (the presence of alkaline corrosion products may be detected by burnishing a pH indicator strip on to the affected surface);
- needle-like crystals and incrustations on the inner surface of the glass - they may also have spalled off, leaving the crystals on the surface of the photograph below;
- blister-like crystals that appear to have a small darker-colored core;
- mold-like masses on the surface of the daguerreotype plate below, sometimes obviously associated with a spalled-off crystal corrosion product from the cover glass above; these have a "bead-and-thread" morphology reminiscent of Candida spp. but are entirely inorganic.
(Refer to Barger; Smith; White (1989) for more information on cover glass deterioration.)
18.104.22.168 Wood Trays
The wooden structure of the case may be found in poor condition, with the front or back surfaces warped, joints broken, structural members split, and glue desiccated and released. Side members are often missing altogether. The paper or leather coverings may have begun to lift from the underlying wood structure.
22.214.171.124 Composite Thermoplastic
Union cases may show warpage, "blanched" or roughened surfaces, cracks or other physical damage (often located at the insertion and attachment points of the brass hinges). Storage for extended periods at higher temperatures or excessive light exposure both seem to be damaging. Prior cleaning and cosmetic treatments may include the application of water, detergents, solvents, petroleum jelly, furniture polish and shoe polish.
126.96.36.199 Brass Preservers, Mats, Hinges and Clasps
The most common deterioration observed on the varnished brass mats are the small randomly distributed spots of brown, black or green copper corrosion products that appear to be under the varnish layer but which may effloresce. less common is the observation of large fields of even discoloration over sections of a mat. The occurrence of local copper corrosion has been linked to contact with the alkaline products of glass corrosion. Tiny holes in the varnish film and exposure to elevated humidity have also been cited as causes for brass corrosion on mats and preservers. Preservers, made from a flexible copper alloy foil, are subject to mechanical stresses and fatigue due to the action of folding and unfolding. The most common deterioration of these components is mechanical breakage, usually occurring at one or two of the corners. Hook-and-eyelet clasps are sometimes found to have been broken; hooks are sometimes missing altogether.
188.8.131.52 Textile Covers for Cushions and Retainers
The most common deterioration seen on velvet coverings is the accumulation of lint, dust and dried accretions. Cushions may be damaged by insects. Retainer coverings may be worn, abraded and compressed; they may no longer provide adequate pressure along the package edge. Silk cushion coverings are sometimes found in a fragile and worn state. While the dyes used on these textiles may be quite sensitive to light, light-induced fading is less frequently encountered because these components have been protected inside the closed cases.
In the following section, it is assumed that all treatments will be carried out by qualified conservators familiar with the materials and characteristics of the objects they are treating. No treatment indications given here can be considered safe for any object without suitable spot testing, careful observations and skilled, judicious application. Removing the package from a case: Cases usually have step joints, not mitred joints, and these tend to be weak. If the package is sound (preserver and/or sealing tape intact) it may be possible to use a small suction cup to gently lift the package out of the case. If it is necessary to use a micro-spatula, carefully work the plate out from the top or bottom end. A microspatula with a small section of the tip bent in at 90° may be helpful in lifting the package out of the tray. Keep a firm grip on the edges of the case to counteract the leverage of the micro-spatula. Do not force the package out. It may be impossible to safely remove the package; if this seems to be the case, stop and reassess the procedure. Disassembling the package: If an object is not in need of preservation or restoration treatment, it should probably not be disassembled. This is particularly true for those few cased photographs that appear to have their original seals present and intact; there are so few objects in this state that conservators must be wary of obliterating potentially valuable historical evidence. If disassembly is to be done, keep the following points in mind:
- make a detailed record of the configuration of the package as disassembly proceeds;
- make sure you can reassemble the components in the orientation in which you found them;
- minimize the stress on the preserver's flaps and corners by working in stages and using a solid vertical support against the side surfaces of the preserver;
- minimize the risk of damaging the plate by carefully removing the opened preserver from the package components, rather than levering the package components out of the preserver; small clips might be used to keep the plate and mat from sliding against one another during preliminary steps;
- sealing/binding tapes should be removed intact so that they might be reused to reseal the package;
- identify and archive, if possible, any glass or paper components that are permanently removed from the package;
- wear clean gloves when handling daguerreotype, ambrotype or tintype plates; latex examination gloves provide better touch sensitivity than cotton gloves but care must be taken to ensure that talc traces are not present on the glove exterior;
- never lay a daguerreotype plate face down;
- after examination or treatment, reseal the package (see Section 184.108.40.206 on resealing) and replace the preserver; ensure that the treatment has not increased the size of the package, producing new stress on the joints of the case.
Leather may be gently cleaned with small swabs dampened with a ethanol/water (1/9) mixture. (Some leather colorants may be soluble in alcohol.) Areas of lifted leather may be reattached to the wood structure with starch paste, polyvinyl acetate (PVA) emulsion adhesive or with methylcellulose paste (3-4% w/v). Where judged appropriate, skinned and abraded areas may be consolidated with diluted PVA emulsion or methylcellulose paste (approximately 1% w/v) and tinted with acrylic paint. Coatings such as microcrystalline wax or diluted PVA emulsion may be used to modify surface gloss. Losses can be compensated with paper infills, either from pulp or from appropriately textured sheets adhered with a diluted PVA emulsion or methylcellulose paste. Paper pulp or tissue can be manipulated and molded while damp to replicate relief elements of the case surface. These can be pre-tinted or tinted with watercolor after application. Watercolor mixed with diluted PVA emulsion may be used to modify gloss. Alternatively, microcrystalline wax or untinted PVA emulsion can be applied over the watercolor to alter the infill gloss. After all other structural and cosmetic treatments have been completed, some conservators may sparingly apply microcrystalline wax that is buffed to produce an even surface finish. For repair of hinges, see Section 220.127.116.11 below.
Losses to the paper covering on the exterior of a case can be filled with paper sheets or pulp in the same way as losses in leather coverings, as described in the section above. Paper mats inside passe-partout daguerreotype packages can be treated as other paper objects, including dry cleaning, washing, bleaching, repairing, infilling, lining and flattening, as required and if possible. Deacidification treatments which leave calcium or magnesium residues should be avoided so as not to introduce potentially harmful materials into the sealed package. Paper mats for tintypes, if they can be safely separated from the plate, can be treated similarly using the full gamut of paper conservation techniques. Decorative paper strips and paper frames used as sealing tapes on passe-partout packages or any damaged original sealing tape can also be treated. Often these tapes will be found to have been split open and inadequately repaired; sometimes later additions of sealing tape will have been applied directly over original tapes. Conventional paper conservation treatments can be used to remove, restore and reuse this original material. Lining damaged original paper strips onto a thin Japanese paper or onto lens tissue with dilute starch paste will allow these components to be reused, either alone or over a new sealing tape. For repair of hinges, see Section 18.104.22.168 below. For resealing, see Section 22.214.171.124 below.
126.96.36.199 Thermoplastic Composite Material (Union case)
Little has been reported about cleaning or repair treatments for this material. B. L. Smith (1994), in a study of these cases, has pointed out some potential problems with aqueous cleaning treatments. She recommends reliance on dry cleaning methods, including brushing, vacuuming and mechanical excavation. Smith cites a successful use of 10% Acryloid B-72 in toluene to repair breakage. Losses have been successfully filled with a two-part epoxy putty, Araldite, which can be toned with acrylic emulsion or acrylic resin paints. Smith also cites a collector using Arcon 140 epoxy tinted with oil paint to fill losses.
While handling glass objects, always ensure that they are well supported. Use a padded board as a work surface. This can be made by covering a piece of heavy cardboard with cotton textile and many layers of lens tissue. The lens tissue can be removed one layer at a time as it gets soiled. Noncorroded glass: Undeteriorated but dirty cover glass may be cleaned and reused. (Note that it may be impossible to distinguish dirt from deterioration with certainty.) Begin by brushing the glass surface with a long-haired soft brush. Always brush from the centre of the plate outward. Clean the glass with wads of cotton wool or large swabs. Use an ethanol/water mixture or an acetic acid solution for cleaning glass. Ethanol improves the efficiency of cleaning and aids in the evaporation of the water. Once the glass is clean, it should be wiped with lens tissue. To check cleaning, breathe on the plate and watch the evaporation. If the vapor evaporates evenly, the plate is clean. Glass cleaning solutions containing ammonium hydroxide should not be allowed to contact the surface of an ambrotype. Corroded glass: Some conservators and conservation scientists advise that cover glass showing signs of corrosion should always be removed and replaced with new glass. Deteriorating glass should not be cleaned and reused as the cleaned, unstable glass will then enter into a new and rapid phase of deterioration. Others recommend that deteriorated cover glass be retained in place, but only if the object is to be stored in a humidity-controlled area (40-55% RH) and will be regularly monitored. In this case aqueous cleaning should not be done, only dry cleaning, in order to avoid starting a new, rapid corrosion cycle. (Contributor Susan Barger notes that cleaning with vinegar -- 5 % acetic acid solution -- followed by polishing is an acceptable practice for corroded glass that is to be retained.) If the object is to return to an uncontrolled environment or if regular monitoring is unlikely, the deteriorated original glass should be removed and replaced with new glass. It may be possible to retain a deteriorating cover glass while separating it from the plate and mat below. This can be done by introducing a transparent barrier such as Mylar or new glass. Note that this might accelerate glass corrosion at the interface. Reverse-painted cover glasses may show paint losses and cleavage, but no glass deterioration; in such cases, the paint can be consolidated and inpainted with acrylic emulsion paints or acrylic resin paints. When reverse-painted cover glass shows evidence of glass deterioration, a copy may be produced on a new glass as a replacement using the paints noted above; spray application of diluted paints using a self-adhesive mask to protect the unpainted aperture produces the most satisfactory result. Where copying or replacement is impossible or undesirable, a transparent barrier may be placed under the deteriorating original cover glass. It should be remembered that even the best quality of replacement glass may itself show signs of deterioration ten to twenty years after its installation. This is due to the unfavorable configuration of having sheet glass adjacent to a small enclosed airspace which is the unavoidable geometry of the cased photograph package. Inspection programs to detect glass deterioration are necessary even for objects that have new cover glass. Also, since replacement is not an absolute remedy to the problem, some conservators argue for intermediate or hybrid approaches which maintain the original components together. If a replacement is to be made, most ordinary modern picture framing glass can be used as long as it is free of flaws and color cast. The edges of newly cut glass should be sanded (use wet/dry sandpaper or a whetstone); this removes the sharp edges that can cut through the sealing tape and provides a better tooth for adherence. Specialty glass, such as anti-reflection glass, is probably an unnecessary expense because it is not significantly more durable than ordinary picture framing glass. Also, cased photographs require carefully controlled display illumination, so there is little advantage to be gained from anti-reflection glass. Some anti-reflection glass is colorless (for example, Tru Vue - Premium Clear). This might be considered when the slight greenish cast often found in common window glass adversely effects the appearance of the photograph. Polymer glazing materials, such as Plexiglas, should be avoided. These scratch easily and do not provide a barrier to corrosive gases. However, note that some contemporary daguerreotypists use acrylic glazing, rather than glass, in their plate housings. All collections of cased photographs should be monitored regularly for glass deterioration. When the support glass of an ambrotype corrodes, there is very little treatment that can be done to alleviate the damage caused by the corrosion. Ensure that the object is maintained in a stable environment with minimal humidity fluctuation.
Broken or detached wooden case components can be repaired using hide glue or PVA emulsion. Repaired joints must be clamped during drying; small frame clamps or elastic bandages, in addition to a variety of small spring clamps, will be useful for this purpose. Missing wooden members can be replaced with balsa wood or with 8-ply matboard, trimmed to fit precisely and covered with paper and finished to match the original case materials. Joints can be reinforced with paper reinforcements applied with PVA emulsion adhesive or methylcellulose paste.
Trays that have opened corner joints and that cannot be closed around a package that is slightly too large may be modified by adding matboard or balsa shims at the opened joints. These can be covered and finished as noted above.
Surface dirt on brass components may be reduced with dry or damp cotton swabs. It may be possible to wash these components in water containing a surfactant to remove heavier soil accumulation; they must be rinsed and carefully dried after water cleaning to avoid initiating or accelerating corrosion. Mats and preservers were usually varnished with tinted shellac; these coatings may be soluble in alcohol or other organic solvents.
Corrosion products that project above the surface of the metal as brittle blisters may be reduced mechanically, using sharpened wooden sticks (preferably hardwood) or pointed scalpel blades or other micro-tools. It may be advisable to coat areas treated in this way; consider acrylic resins (Acryloid B-72; B-67; B-48N) or Incralac, which contains benzotriazole (BTA) -- a corrosion inhibitor.
Inpainting may be done with "metallic" pencils; acrylic paints; gouache paints; acrylic resin Acryloid B-72 or methylcellulose mixed with bronze powders; or acrylic emulsions Rhoplex N580/AC-33 (1/1) mixed with Mica Pigments. An appropriate isolating layer should be used beneath all inpainting.
Where a burr on the verso edge of the mat aperture has produced scratches on a daguerreotype plate surface, further damage can be avoided by several measures:
- the sharp edge may be dulled or rolled forward with a stainless steel burnisher;
- a sheet of spacer material can be custom cut and introduced underneath the mat; use one of the thicker nonwoven polyester web materials;
- several thin spray applications of Acryloid B-72 to the sharp edges will even out the surface.
Broken preservers may be repaired with a viscous Acryloid B-72 formulation (HMG adhesive) and brass foil. The exterior surface of the broken corner is temporarily taped together, then a small L-shaped piece of brass foil is pressed into place on the interior side, molding it into the three-dimensional conformation of the stamped design with a bone folder or other appropriate shaping tool. The reinforcing foil is then removed, coated with the viscous adhesive on the contact surface, pressed into place and allowed to dry. This process can be repeated to provide further reinforcement.
The cushions and retainer strips inside the case may be first cleaned by blowing loose dirt away with a rubber bulb blower or by using a Mini-Vac equipped with a plastic pipette attachment. More solidly adhered debris might be removed using a medium bristle brush. Water treatments are not advised. Stained areas on the retainer may be successfully "overpainted" with pastel pencils. Missing textile cushions and retainers can be reconstructed using acrylic or cotton velvet, high-quality 2-ply matboard and cotton batting. Such reconstructions should be carried out with the collaboration of a knowledgeable curator or custodian.
188.8.131.52 Repairing Broken Hinges
If the trays are completely detached from each other, begin by lifting the original covering material along the interior and exterior hinge edges. Whether the case is covered with leather, cloth or paper, the material is usually very thin and easily torn through. It is important to work slowly to control the lifting. Dampening the material frequently with an ethanol/water (1/1) mixture may help prevent delamination. Once the hinges are lifted, introduce the repair material.
In choosing the repair material, consider strength and flexibility requirements, and compatibility with the original material. Choices for repair materials include:
- bookbinders' repair vellum sanded to tissue thickness;
- lightweight Japanese paper or 40 gsm Silversafe paper (cut with machine direction perpendicular to strip);
- thin nonwoven polyester web material, such as Cerex or Reemay;
- if the broken hinge is a simple leather strip, consider using a strip of new, properly toned leather as replacement.
The most common repair adhesives are PVA emulsion (usually diluted), methylcellulose and starch paste. The choice of adhesive depends on flexibility requirements and on the repair material chosen. The repair material is cut in strips of appropriate width and adhered to the wooden surfaces. The repair strip is then covered with the flaps of the original covering. Weight the repair after readhering the flaps. If both inner and outer hinges are to be repaired, start by repairing the outside hinge, then repeat this procedure for the interior hinge.
Illustrations: Toshiaki Koseki
Prepare infills as outlined in Section 184.108.40.206 and tint the exposed areas of the repair with watercolor, watercolor in dilute PVA emulsion, acrylic emulsion paint (Liquitex gloss medium) or tinted wax.
220.127.116.11 Repackaging Plates
For daguerreotypes, two distinct approaches to repackaging exist. In one approach, the sealed daguerreotype package contains no hygroscopic material, thus avoiding the presence of a reservoir of moisture inside the package that could drive the various processes of metal corrosion. This practice reflects the original format of cased daguerreotypes where no paper products, except the sealing tape, were included in the package. The other approach is to intentionally include a quantity of high-quality unbuffered matboard inside the sealed package (but not in direct contact with the daguerreotype image surface). This acts as a humidity buffer inside the package, helping to dampen relative humidity fluctuations inside the package. This practice reflects the original format of passe-partout packages, which contain substantial quantities of paper, cardboard and adhesives. Whatever repackaging method is chosen, it is essential to ensure that all of the package components are well secured and will not slip or shift. Mechanical damage due to component slippage is a common phenomenon in cased photographs and avoiding future occurrences should be a major criterion in choosing a repackaging method.
18.104.22.168.1 Non-hygroscopic Package
This method uses a moisture-resistant barrier on the back of the package and does not introduce any hygroscopic material inside the package. A 5 mil Mylar backing is cut to be slightly smaller than the plate. If a barrier is required to prevent abrasion of the plate surface (see Section 22.214.171.124), use a layer of a nonwoven polyester web material. The package is closed with a moisture-resistant sealing tape (see Section 126.96.36.199). This style of repackaging has the advantage of adding little or no extra thickness and allowing the plate verso to be seen without disassembling the package. Marvelseal, a nylon/aluminum/polyethylene laminate, has also been used as an impermeable backing, but it lacks the advantage of transparency. If the plate is much smaller than the package, this method is difficult to use.
188.8.131.52.2 Humidity-buffered package variant
Modify the package described above by including a rectangle of matboard cut to precisely fit between the verso of the daguerreotype plate and the Mylar. Use high-quality matboard that does not contain alkaline pH-buffering compounds and that has been conditioned to an appropriate moisture level. Use a matboard thickness that will not add significantly to the package thickness if the plate is to be returned to a case.
184.108.40.206.3 Matboard Sink
This variant is most useful in the repackaging of passe-partout style packages and stereo-daguerreotype packages. A multilayer matboard structure is made that holds the plate in correct register, provides maximum support for all edges and for the plate verso surface, and provides a separation between delicate surfaces and the glazing material. Use rectangles of high-quality, unbuffered 2-, 4- and 8-ply matboard cut larger than the finished package size to create a sink cavity for the plate. Use a layer of a nonwoven polyester web material to provide separation between the plate and any original package components that may cause abrasion or scratches. Adhere these layers with 3M Double-sided Tape No. 415, starch paste adhesive, methylcellulose paste or PVA emulsion adhesive. It is essential to add only the minimum possible additional thickness to the package if it is to be returned to a case.
220.127.116.11.4 George Eastman House Housing
The Conservation Department at the George Eastman House has developed an elegant structure for housing unpackaged daguerreotype plates that combines some features of both approaches outlined above. This housing was inspired by a unique metal and paper housing associated with the American daguerreotypist Robert Cornelius. A matboard sink mat is made with cavities for the daguerreotype and for the cover glass. (See drawing on next page.) The daguerreotype cavity is slightly deeper than the total thickness of the plate, including its bevelled edges. The cover glass cavity should be the same depth as the glass thickness. A 5-mil Mylar cradle holds the edge of the plate and prevents it from moving inside the slightly oversized cavity or from contacting the inner surface of the cover glass. The cradle is made from two sheets of Mylar. One is cut to the width of the plate and folded at the top and bottom edges to form a Z-shaped spacer or spring; the other is cut to the height of the plate and is folded to form "Z" springs at the sides of the plate. The ends of the Mylar sheets should be trimmed to fit precisely into the spaces of the cover glass cavity. Once the cradle, the daguerreotype plate and the glass are precisely fitted into the matboard sink structure, the glass is sealed to the top surface of the matboard with paper tape. This system can be adapted to include an original brass mat behind the cover glass. The finished package can be easily overmatted and framed for display.
Illustration: George Eastman House
Reusing original tapes: This should be done when possible to preserve the original package components. It may be possible to change a deteriorated cover glass by releasing the tape from the front with minimal solvent application, removing the glass, fitting in the new glass and reactivating the original adhesive to secure the new glass. Damage on the original tape can be repaired using conventional methods. If original binding tapes must be removed and replaced with new materials, consider storing the removed tape fragments in the case tray, behind the package. Self-adhesive tapes: Many conservators prefer pressure-sensitive tapes for sealing cased photographs because they are easier to handle than paper tapes made with wet adhesives and they do not introduce moisture into the sealed package. Paper tapes such as Filmoplast P-90, Filmoplast P-91 or Filmoplast T (textile carrier) have been commonly used to reseal cased photographs. Polyester-backed or Mylar-backed tapes provide some moisture barrier. Notable among these are the 3M Polyester Tape No. 850 (Silver), which is thin and flexible. It may be preferable to isolate the edge of the daguerreotype plate from contact with the adhesive. This can be done by laying a thin strip of nonadhering material down the centre of the sealing tape. Use 3-mil Mylar, Hollytex, Japanese paper or a thin strip of the sealing tape itself, turned so that its nonadhesive surface contacts the plate edge. See application instructions under "Plain paper tapes" below. Self-adhesive tapes can be used alone or be covered with the original paper sealing tape that has been removed and treated as described in Section
18.104.22.168. These auxiliary paper seals may be adhered with diluted PVA emulsion adhesive, methylcellulose paste or with a mixture of wheat starch paste/methylcellulose/PVA emulsion (3/3/1). Plain paper tapes: Note that the use of aqueous adhesives may produce an unavoidable exposure of the package components to moisture. Consider using the alternatives described above. Choose an appropriate paper. Examples are: Renaissance paper; 40 gsm Silversafe; a decorative paper tape, lined onto more stable or stronger paper if necessary. Paper tapes should be cut across the grain (machine direction perpendicular to the length of the strip) to give the maximum strength across the seal. Choose an appropriate adhesive. Examples are: wheat or rice starch paste; PVA emulsion (undiluted); methylcellulose paste; mixtures of starch paste, methylcellulose and PVA emulsion. Starch pastes should be used stiff and be applied sparingly. (If there is any risk of the adhesive wicking between the package layers, the wet adhesive method should not be used or try using the non-adhesive strip technique described previously.) Place one edge of the plate package on the pasted tape and walk the plate around it until the strip is adhered to the edges in a continuous band. A weak clamp applied (with a cushioning barrier) to one edge of the package may help. Trim the excess length away before laying down the last section of the strip; there should be a slight overlap of paper where the ends of the strip come together. Lightly rub the edges to set, taking care not to tear the paper. Pinch the corners so that they come together in a triangle that is perpendicular to the plate package. Cut the triangles with a pair of scissors at a 45-degree angle. Working around the plate, lift one edge of each corner and push the other edge underneath it. This will enable the corners to lay flat. Let the tape air dry for at least one hour before trimming or tinting. Make the trimming cut with a very sharp scalpel, being careful not to scratch the glass. If the tape is to be tinted, apply the paint before removing the excess strip; the waste paper will act as a guard for the glass and allow the tinting medium to absorb into the cut edge of the tape. When the tape is dry, remove the excess strip.
2.3 Daguerreotype Plates
Daguerreotypes are direct positive photographs on metal supports. The supports are copper plates clad with a polished layer of metallic silver. The image particles, which lie on the surface of the polished silver, constitute the image highlights; they are primarily composed of silver but may contain small amounts of gold and mercury. In highlight areas, the silver image particles scatter incident light and appear to be white, while in the shadow areas the polished silver reflects light like a mirror; when the plate is positioned to reflect a dark surface, the image appears as a positive. Image particle size and spacing are in the same order of magnitude as the wavelengths of light; this may result in the appearance of physical (noncolorant) colors in the image through diffraction effects, particularly in highlight (high particle density) areas. Fine parallel polishing lines are typically observed on daguerreotype plates. They are generally horizontal across the image, since the plates were designed to be looked at using a light source positioned to the side, rather than above, the image. These marks should not be confused with damage. During plate preparation, a silver electroplating step may have been employed; this will usually be signalled by the presence of a dull silver layer on the plate verso. From 1842, daguerreotypes were routinely "gilded" -- treated with a solution of gold chloride. This procedure, which heightened the image contrast, also seems to have improved the resistance of the plate to tarnishing and hardened the image particles against physical disruption. Daguerreotypes were sometimes hand-colored by the careful application of dry pigments mixed with gum arabic; colored areas may have transparent overcoats applied. Most daguerreotype images are laterally reversed; some late daguerreotype cameras included a mirror system to correct the image reversal.
22.214.171.124 Daguerreotype plate size designations
Because of the approximate way in which the silvered plates were cut down by daguerreotypists to make smaller formats, the confusion between metric and imperial units, and the existence of at least two sets of standards, there are some discrepancies in the published dimensions of daguerreotype full plates and fractions. The regular American "whole-plate" (or "full-plate" or "4/4") is 8½ x 6½ inches. The half-plate (6½ x 4¼), quarter-plate (4¼ x 3¼) and eighth-plate (3¼ x 2 1/8 ) sizes are simple divisions of the full plate. The sixth-plate (3¼ x 2¾), ninth-plate (2½ x 2) and sixteenth-plate (1 5/8 x 1 3/8) formats are not simple fractions. The sixth plate is the most common studio portrait format.
Another set of plate formats derives from the "Imperial" (or "Mammoth") plate that measures 14 x 11 inches. A 14½ x 16½ inch plate is also reported. Plates exist which are as large as 16 x 24 inches. Panorama format plates also exist. See references in Buerger, Kempe and Rinhart (1975) on these formats.
Note that plates may have been precut by the plate manufacturer, in which case they will often show the manufacturer's name and a plate grade as blind-stamps in one corner. (Higher grade numbers indicate thinner silver layers on the copper plate.) Alternatively, the daguerreotypist may have done the cutting. These plates usually lack the manufacturer's identification; they may be irregular in shape and may deviate from any standard dimensions.
Stereographic images were sometimes made in multiple image (nonstereograph) cameras, then cut and realigned to create a stereographic effect. When removing these from a package for treatment, ensure that the plates can be unambiguously identified for return to the package in their proper orientation. A carefully recorded diagram of the relative spacings of the plates within the package should be included in the pretreatment documentation. The stereo effect may be checked by observing the image through a stereoviewer.
126.96.36.199 Metal Plate
Daguerreotype plates are manufactured by the "Sheffield plate process" in which a thin layer of silver is fused to a copper ingot by heat then rolled to the desired plate thickness. Exfoliation may occur; in this condition the topmost silver layer carrying the image particles separates from the underlying silver layer which remains bonded to the copper support. All types of metal supports are subject to mechanical distortion from bending or other types of mechanical working. Mechanical distortion frequently results in damage to image layers. All types of metal support materials used for photographs are subject to corrosion or degradation caused by the oxidation of the metal itself. In daguerreotypes, this may be seen as films, spots and blister-like growths on the plate surface. The daguerreotype's silver surface is susceptible to tarnishing. Tarnish products, primarily silver oxides, may cover the entire plate or be concentrated at the edge of the mat window opening. Thin, evenly deposited tarnish films are characterized by a series of interference colors. The most brilliant series of colors occur where the tarnish layer is thinnest. Thicker, more uneven tarnish films appear pale grey or black, the color of bulk silver oxides. The alkaline gels and silicate crystals formed by weathering corrosion on the inner surface of the cover glass may spall off onto the daguerreotype surface, where they can initiate various types of metal corrosion. One form of such corrosion are the mold-like masses previously noted in the discussion of cover glass corrosion (Section 188.8.131.52). Barger; Smith; White (1989) report deep dendritic fissures in the daguerreotype surface where these masses have grown. Other forms of corrosion on the plate surface may result from the transfer of glass corrosion products. These may show as variable-size grey spots on the plate that may be nucleated and may have associated accretions. Note that grey spots may also derive from splashes of mercury deposited on the plate during processing
Some daguerreotypes develop green-colored blister-like growths. These are due to copper corrosion formed at tiny holes in the silver layer of the plate. Bronze powder particles may produce similar corrosion products.
Various chemical cleaning treatments may have produced microscopic pitting of the silver surface. This may be manifested as a lowered overall image contrast or by the appearance of a white, cloudy "veil" over the image.
Daffner; Kushel; Messinger (1996) have noted a bright fluorescence on some daguerreotype plates under short-wave UV illumination (UVC; 200-280 nm.).
The significance of these observations is not yet entirely clear, but the authors associate the fluorescence with previous chemical cleaning treatments, prolonged exposure to the environment, general mishandling and the presence of cyanide compounds.
184.108.40.206 Image Layer
Daguerreotypes do not have a binder layer; instead, the image particles of the daguerreotype are formed directly on the surface of the daguerreotype plate. The daguerreotype surface has a micro-scale roughness due to the topography of the image particles.
220.127.116.11 Silver Image
The image particles found on a daguerreotype plate are 0.1 μm to 50 μm in diameter (roughly 10 to 100 times larger than those found in other types of photographs). Daguerreotype image particles are primarily composed of metallic silver but may include small amounts of gold and mercury. Image particles are susceptible to mechanical abrasion.
Daguerreotype image particles are susceptible to oxidative corrosion, as described above for the silvered plate (Section 18.104.22.168).
Residues from thiourea cleaning may cause spots, or "measles," on daguerreotype surfaces. As the plate is repeatedly cleaned with cyanide- or thiourea-based chemical cleaning solutions, the image particles are reduced in size and their spacing increases, resulting in reduced image contrast.
Residues from cyanide and thiourea cleaning also leave corrosive films on the entire plate surface.
The daguerreotype image does not fade due to light exposure.
A variety of protective coatings were initially proposed for daguerreotypes before the introduction of gilding. These included varnishes of copal and other resins and glues. This was not widely practiced, and coated plates are extremely rare. Some modern materials have been tested for use as protective coatings for daguerreotypes and are not recommended.
22.214.171.124 Paint/Pigment components
To color the surfaces of daguerreotypes, pigments were ground into a fine powder with gum arabic and applied dry to the surface of the images. In one application method, the colorist breathed lightly over the area to warm and humidify the gum, thereby activating the adhesion of the powder to the plate. Colorants are sensitive to light, moisture and abrasion.
"Shell gold" (metal powder in oil or gum arabic solution) was used to highlight selected image areas, such as buttons and jewelery. A sharp tool may have been used to scratch into the image surface to create highlights and to reinforce or create image elements.
126.96.36.199 Photographing Daguerreotypes
Reprography of daguerreotypes is complicated by the appearance of reflected images of the copy camera, copy photographer, etc., in the daguerreotype plate, as well as by misleading exposure readings from "through-the-lens" (TTL) camera light meters.
The plate should be oriented with the direction of the final polishing marks -- usually horizontal across the image -- parallel to the direction of illumination from the photographic lights to minimize their appearance in the copy photograph. The lights should be positioned at approximately 45-degree angles from the image plane, as with other reprography. Polarizing filters on the light sources can be used to suppress physical damage on the plate surface, so they may be useful for making publication-quality reproductions where the intent is to give the best possible representation of the image. (Fully polarized light reprography, with parallel filters on both sources and lens, results in a distorting increase in image contrast.) Similarly, photographing the plate while it is immersed in an inert solvent, such as heptane, may suppress reflections and physical damage. All such image modification techniques are inappropriate for photo-documentation of conservation treatments.
Colored tarnish films may be reproduced only poorly, or not at all, by color photographic materials. Color filters could be used to enhance the photographic reproduction of daguerreotype corrosion films, but no work has been published on this subject. Optimizing the specular reflection off the plate surface may allow tarnish films to be recorded more clearly.
A low-reflective black mask or shroud should be fitted to the camera lens barrel to reduce unwanted reflections in the plate. Use something like black felt mounted on cardboard or use an empty black photographic paper box -- 8x 10 x 3 inches. A filter holder may be useful to arrange the mounting of the mask on the lens barrel. All ambient illumination in the room should be turned off to avoid unwanted reflections off the lens into the plate.
The mirror-like reflection from the plate will result in TTL light meters indicating exposure readings that are too large; reduce exposure by approximately 1½ stops from the indicated reading. (Incident light measurements are not subject to this adjustment.) Record the pretreatment exposure used and manually set the same exposure for mid- and post-treatment photographs; this is necessary, since exposure measurements taken from the plate may change as treatment proceeds.
See Daffner; Kushel; Messinger (1996) for details regarding the photographic recording of fluorescent patterns on daguerreotype plates.
Daguerreotypes, like all cased photographs, are composite artifacts having complex reactions to environmental conditions. Conditions that are optimal or harmless for one component may be damaging to another. Environmentally induced deterioration processes in one component may cause reaction products harmful to another component to be released.
Heat alone is not a primary determinant of deterioration for daguerreotypes, although sustained elevated temperature may accelerate the corrosion of thiourea- or cyanide-cleaned plates. High temperatures may cause desiccation of case components. Very high temperatures can cause dimensional fluctuations that may contribute to image exfoliation on plates that have been excessively treated with gold.
Cycling ambient temperature produces the relative humidity cycles in the microclimate of the sealed package that are a major driving force behind the weathering corrosion of cover glass. The glass corrosion, in turn, causes metal corrosion on the plate.
Lower storage temperatures will retard deteriorative processes of paper and leather components. There is no reason why daguerreotypes cannot be housed in RH-controlled low-temperature storage areas. (These facilities must be equipped with appropriate transition climates to avoid transitory high humidity conditions when items are removed to normal temperature areas.)
188.8.131.52 Relative Humidity
In all types of cased objects, high relative humidity will contribute to deterioration of unstable glass, as well as corrosion of metal supports, mats and preservers. The leather, paper and wood components of cases will swell and shrink with fluctuating humidity, and they may become embrittled at low humidity. Leather can be structurally weakened at high humidity. Relative humidity above 60% can sustain mold growth.
High humidity can contribute to tarnishing and other corrosion processes of daguerreotype plates.
The major driving forces behind glass corrosion are moisture and fluctuations in relative humidity. Water (from moisture in the air) interacts on an atomic level with the glass surfaces, initiating glass corrosion cycles. Glass is best maintained at moderate relative humidity (40-50%) without excursions to higher or lower humidity.
For a mixed collection of daguerreotypes, ambrotypes and tintypes, 40% RH seems the best compromise condition. If possible, minimize the difference between the humidity conditions in the storage area and the areas where the objects are used for reference and display.
184.108.40.206 Environmental Pollutants
Atmospheric pollutants can cause image deterioration in all types of cased objects. Sulphur dioxide, a common pollutant, can combine with oxygen and moisture to form sulphuric acid, which is particularly damaging to leather and paper. The silver image material of all cased photographs may be damaged by the ammonia, ozone, sulphur dioxide and nitrogen oxides generated in industrial environments.
The silver images of daguerreotypes react with airborne oxidizing gases.
A daguerreotype that is well sealed and boxed will be relatively free from harm by airborne pollutants. However, the source of corrosion-inducing pollutants may be the materials composing the package and case. These should be removed or isolated from the daguerreotype plate. Some preliminary investigations were done into the use of an activated charcoal "scavenger" within the daguerreotype package. (See Mustardo.)
Although daguerreotype images are not sensitive to light, the pigments used for hand-coloring are frequently quite fugitive. The paper and textile components of the packages may also be light sensitive. Daguerreotypes with broken glass or seals may have an increased potential to tarnish if they are strongly lit and kept in a polluted atmosphere because light accelerates the formation of silver sulphide in the presence of unreduced sulphur gases.
220.127.116.11 Storage Containers
Packaged daguerreotypes may be stored flat inside Solander boxes equipped with Ethafoam layers cut out to create cavities in which the cases fit snugly. The interior surface of the cavity is lined with a fine unbleached cotton textile to provide a nonabrasive surface. In boxes containing daguerreotypes, the interior of the Solander box lid may be lined with Pacific Silver Cloth (or equivalent) to provide a scavenger for oxidative gases entering the box (also, see "zeolites" below); the brown cloth also provides a dark surface to reflect on the daguerreotype images for optimal viewing.
Alternately, custom-made individual matboard boxes of the clamshell or slipcase variety may be constructed to house daguerreotypes. A four-flap enclosure adapted for housing cased photographs is used at the Harry Ransom Humanities Research Center. (Brown, 1996) This method is well-adapted for storing cased photographs on their edges, a measure recommended by some conservators to reduce glass corrosion-induced damage on the plate surface.
Padded plastic wrappings should be used only with caution. One instance has been noted of severe corrosion of daguerreotypes caused by the off-gassing of plasticizers used in plastic wrapping, even though these were described as "archival." However, food-grade polyethylene "zip-lock" bags have been successfully been used to store polished silver objects. As long as appropriate tests are carried out on the specific product used, these may provide inexpensive and effective protection for stored daguerreotypes.
Conditioned sheet-form silica gel might be included in the bags as a humidity buffer. Likewise, boards and papers containing molecular sieves (zeolites) may be included in closed packages to sequester oxidizing gases.
In the following section, it is assumed that all treatments will be carried out by qualified conservators familiar with the materials and characteristics of the objects they are treating. No treatment indications given here can be considered safe for any object without suitable testing, careful observation and skilled, judicious application.
Note that plates that were not gilded have particularly fragile image surfaces. Nongilded plates sometimes show lower apparent image contrast, or they may show more areas of physical image loss than gilded plates. However, it is usually necessary to resort to instrumental analysis, such as X-ray fluorescence spectroscopy, to determine the presence or absence of gold.
Note that some connoisseurs consider the presence of coherent tarnish layers on the periphery of a daguerreotype image to be an enhancement of the aesthetic qualities of the object, particularly when the tarnish shows a series of smoothly gradated interference colors. The decision to remove such tarnish should be made only by a fully informed owner/custodian. In many cases, such tarnish films should not be removed. The presence of original and intact sealing materials should also weigh heavily against a decision to open a package in order to perform cosmetic treatments.
Plates that do not exhibit exfoliation can be dusted to remove loose debris. The preferred method is to use a gentle stream of air from a rubber bulb syringe. Alternately, a controlled low-pressure stream of air can be had from the airbrush attachment on a suction table. A clean airbrush should be reserved exclusively for cleaning daguerreotypes, and its air hose should be equipped with a moisture trap.
18.104.22.168 Washing and Drying
To remove adhered accretions and some of the transferred products of glass corrosion, uncolored daguerreotypes may be safely washed in distilled/deionized water or in a pH 8.5-10.0 solution of ammonium hydroxide in distilled/deionized water. Five to fifteen minutes of immersion accompanied by gentle agitation of the wash tray will be sufficient to remove many water soluble accretions. The alkaline wash should be followed by a brief rinse in a bath of distilled/deionized water. This is followed by two or three rinses or an immersion in very clean absolute ethanol. (Some conservators use acetone instead of ethanol or follow the ethanol rinse with an acetone rinse.) Set the plate upright at a slight angle with a blotter underneath the bottom edge to drain. Note that there is a tendency for water to condense in tiny droplets on the plate surface during the alcohol/acetone evaporation when the ambient relative humidity is high enough; if this happens, use a gentle stream of warm air from a hair dryer to warm the plate while the solvent evaporates. Always apply the warm air stream to the verso surface of the plate rather than risk blowing dust particles onto the image surface. The daguerreotype surface can be permanently marred by drying marks, so drying must be carried out very carefully.
Colored daguerreotype plates can sometimes be immersion washed in heptane to dislodge the surface particles not dislodged by dusting; careful color testing is required. Before undertaking this procedure, consider whether it is likely to provide useful cleaning.
22.214.171.124 Chemical cleaning Methods
The most common method used to remove tarnish from daguerreotypes has been the application of a "silver-dip," a solution designed to remove tarnish from ornate silver objects. These solutions were originally made of cyanide compounds and, after the early 1950s, were made of thiourea in a mineral acid. Both cyanide cleaners and thiourea cleaners etch the daguerreotype plate, causing irreparable damage to the plate's surface, and leave behind insoluble compounds; these residues initiate new corrosion on the daguerreotype surface. Such methods should never be used. See Edmondson; Barger (1993).
126.96.36.199 Aluminum Tray Electrolytic Cleaning
Silver corrosion products may be removed by electrolytic cleaning in an aluminum tray filled with an ammonia solution. Use an uncoated aluminum baking container. The most concentrated solution of ammonia that can be used in the procedure is prepared by adding one part concentrated ammonium hydroxide (approximately 30%) to two parts of distilled/deionized water. (Note that a fume hood is necessary.) Slower cleaning actions will be obtained by using weaker concentrations of ammonium hydroxide. The daguerreotype plate is placed face up in the aluminum tray; the copper surface of the daguerreotype must be close to the aluminum tray for the electrolytic cell to be established. The ammonia electrolyte is poured into the tray to cover the daguerreotype. The corrosion product removal can be monitored visually as it proceeds. Hydrogen bubbles are evolved from the aluminum as cleaning proceeds. As grey oxides build up on the aluminum surface underneath the plate, the rate of cleaning will decrease; it may be necessary to move the plate to another position in the tray to allow cleaning to proceed. The reaction rate can be slowed by using a more dilute electrolyte or by using a smaller aluminum tray. Note that the cleaning action progresses from the edge of the plate inwards towards the center of the plate. This may mean that a full-plate daguerreotype cannot be completely cleaned using this method. Electrolytic cleaning might be used as a preliminary step before considering a decision to proceed with electro-cleaning (see below). Electrolytic aluminum tray cleaning should not be used on ungilded plates.
Electro-cleaning, as outlined in Barger; Giri; White; Edmondson (1986), is based on a well-tested method for cleaning metal that has been adapted for the special requirements of daguerreotypes. In this process, the daguerreotype plate is made to be one electrode of a direct current electrical circuit; the second electrode is a silver wand used to direct the cleaning action. The circuit is completed by placing the daguerreotype and wand in a solution of ammonium hydroxide. The wand and plate do not directly contact each another. When a reversible DC current is applied through the circuit, cleaning is effected by forming and dissolving layers of silver oxide in a controlled manner. The method leaves no chemical residues on the plate surface. The method produces a micropolishing effect, in which tiny irregularities in the silver surface are evened out by a combination of silver removal and redeposition on a very small scale. This leaves the plate less susceptible to future corrosion. Some conservators have reported the appearance of translucent white "veils" overlying previously tarnished image areas after the application of electro-cleaning. The nature of this phenomenon is unclear. It has been suggested that copper ions, released into the electrolyte solution during cleaning, might be redeposited on the image surface. (Heller, 1988) While this seems unlikely to happen, given the electrochemistry of the system, the suggestion has been made that the copper surface of the plate be "stopped out" with silicon rubber before treatment. (Note, however, that most silicon sealants evolve acetic acid as they cure.) The significance of silver redeposition is also the subject of some debate. The procedure is carried out (in a fume hood) using a glass tray filled with an electrolyte solution made of one part concentrated ammonium hydroxide (approximately 30%) added to two parts of distilled/deionized water. A DC power source should produce between 2-5 DC volts. Cleaning action should be controlled by monitoring the current read on an ammeter in the circuit. The current is determined by the distance between the end of the wand and the daguerreotype plate surface; in both anodic and cathodic phases, the current should be maintained in the range of 8-25 milliamperes (mA). Regular switching of the current direction is nescessary for the cleaning action to take place. If some mechanical action is required to move the loosened tarnish products off the plate surface and into the solution, this should be done with a soft brush or by using an rubber bulb syringe to force a stream of electrolyte over the surface while cleaning. The direction of the brushing action should be the same as that of the final polishing marks. Heavily tarnished areas may be susceptible to abrasion. Contact between the silver wand and the plate during cleaning will produce sudden increase in current and will damage the image. Such current surges can be prevented by using a constant-current power source or by adding appropriate fuses or resistors to the device. Electro-cleaning cannot be used on hand-colored daguerreotypes or on plates that have not been gilded.
188.8.131.52 Hydrogen Plasma Reduction Cleaning/ Physical Sputter Cleaning
Two variations of cleaning daguerreotypes using plasmas have been used for a number of years in Europe. Hydrogen plasma reduction cleaning results in oxidized silver being chemically reduced to silver metal. Physical sputter cleaning uses a chemically inert gas plasma, such as argon, to physically remove corrosion from the daguerreotype surface. These methods may be applied to hand-colored daguerreotypes. Both require sophisticated equipment to contain the plasma, and to create and maintain a high vacuum environment, as well as specialized operating technicians.
While several groups researching both these methods have observed that some daguerreotypes treated in plasmas develop white surface films, it seems that the hydrogen plasma cleaning procedures do not produce microetching in the silvered surface. The advantage of hydrogen plasma reduction cleaning over other cleaning methods is that oxidized silver is reconverted to silver, not removed from the plate.
184.108.40.206 Repackaging of plates
See Section 220.127.116.11
See Section 18.104.22.168
2.4 Ambrotype Plate
Ambrotypes are direct positive photographs produced in the camera on a transparent or colored glass plate. The glass is coated with collodion (a cellulose nitrate solution), which is then sensitized, exposed and developed.
Physically developed silver forms the image highlights; this image silver was made to appear lighter in color by using diluted developers, development retarding agents, whitening agents (such as mercuric chloride) or cyanide fixers. After development, the image is fixed, dried and varnished. Placed against a dark background (fabric, paper, pigmented lacquer), the light colored silver image appears as a positive. Sometimes the collodion was left unvarnished. Paints or dry colours may have been applied before or after varnishing.
An albumen substrate layer was sometimes used to improve the adhesion of the collodion to its glass support.
The image-carrying layer may be on the surface of the glass closest to the viewer, in which case the image will be laterally reversed and the package will require a cover glass. These may be referred to as "double plate" ambrotypes. Sometimes the plate is positioned with the image-carrying layer on the interior side of the package; this corrects the image reversal and eliminates the need for a cover glass. These may be called "single plate" ambrotypes.
The arrangement and treatment of the various layers inside the ambrotype package were subject to many variations. ("Ambrotype" originally referred to an American variant patented by James Ambrose Cutting. Other variants of the process were called alabastrine process, amphitype, lampratype, relievo.)
Ambrotypes were sometimes made on blue-, red-, orange-, green- or purple-colored glass (the latter being called "Bohemia glass" or "ruby glass"). Ambrotypes made on dark-colored glass do not require a dark backing. One contributor observes that these plates are often unvarnished and, as a result, show more extensive silver image deterioration.
Ambrotype plates may be adhered overall to another plate of glass with Canada balsam, a natural resin adhesive. (This is the subject of the Cutting patent.)
In the relievo variant, all of the image-carrying layer representing the mid-tone background behind a portrait subject was scraped away. This allowed the figure to "float" on the dark field of the added backing and lent a sense of depth to the subject.
22.214.171.124 Glass support
(For notes on the condition of nonadhered cover glass, see Section 126.96.36.199.) The glass used to make ambrotype plates was usually commercially available pane glass. There were some companies that sold "photographic" glass -- this meant that the glass was free of physical flaws and was relatively colorless, not that the glass had superior durability or corrosion resistance. Glass supports of all types are susceptible to physical damages such as breaking and chipping. Some glass formulations are chemically unstable due to a high flux content, especially those with a high ratio of sodium flux in proportion to the alkaline earth flux (calcium and magnesium oxide). Note that glass with a high sodium content produces a yellow-orange fluorescence under UV illumination, whereas glass with a higher alkaline earth content tends to produce orange-magenta fluorescence. Glass corrosion is caused by inherent instability linked to unfavorable environmental conditions. Writing about the condition of glass in collodion wet-plate negatives, M. H. McCormick-Goodhart states, "The collodion and varnish coatings applied to the glass typically prevent the image bearing side of the plate from exhibiting the 'weathered' or 'weeping' glass appearance observed on daguerreotype cover glasses. Nevertheless, alkali leaching from the glass and diffusing into the collodion and varnish layers promote chemical changes in the coatings. The weakened coatings are prone to crazing, cracking, flaking and gradually increasing varnish saponification even though just a small fraction of the glass substrate is involved in the reaction. A hydrated 'silica-rich' layer forms at the original collodion-glass interface, and this layer may also contribute directly to the collodion's adhesion quality, because it is microporous and hygroscopic in nature." (McCormick-Goodhart, "Glass Corrosion . . .," 1992, p. 264)
188.8.131.52 Collodion image-carrying layer
Collodion film is a form of cellulose nitrate produced from a solution of pyroxylin (cotton treated with mineral acids) dissolved in ether and alcohol. Collodion is soluble in many organic solvents. Unvarnished collodion is extremely susceptible to mechanical abrasion. The collodion binders of ambrotypes and tintypes may be chemically unstable, particularly if excess alcohol was used in preparing the solution. Ambrotype collodion layers may be chemically altered by glass corrosion at the glass-collodion interface (see above). All these influences may result in the collodion layer cracking or flaking. Collodion may yellow and become more opaque with age, causing a decrease in image contrast.
184.108.40.206 Silver image
The physically developed silver particles of ambrotypes are larger than the colloidal photolytic silver particles typical of printing-out processes. Normally the silver images of ambrotypes, when properly processed, do not fade or discolor. However, they may exhibit silver corrosion, especially if the image is unvarnished. Residual processing chemicals in the collodion layer, especially sodium thiosulfate, may cause staining and fading of the silver images. One contributor has observed instances of ambrotypes which have converted to a bright yellow color.
220.127.116.11 Coatings (pigmented lacquer and clear varnish)
Pigmented lacquer (frequently made from lamp black pigment mixed in bitumen, asphaltum or linseed oil) was often used on the verso side of the clear glass support. Deteriorated lacquer may exhibit crazing and flaking, especially if it contains asphaltum. Deteriorated lacquer may also damage the collodion image layer if these layers are adjacent. Many ambrotypes have a clear varnish applied on the collodion image layer; white shellac, dammar, sandarac and copal were commonly used. The varnish saturates the image by increasing gloss, and protects the underlying collodion layer and its silver image from physical damage and chemical deterioration. Ambrotype varnishes are applied as "spirit varnishes" which have a small amount of varnish resin dissolved in a solvent. The varnish was flowed onto the collodion image surface, forming a film considerably thinner than a brushed varnish. Varnishes may be chemically altered by glass corrosion at the glass-collodion interface (see Section 18.104.22.168 above). Deteriorated varnishes may exhibit discoloration, crazing, flaking or partial liquefaction (saponification). They may also damage or obscure the underlying image layer. Varnish layers can lose gloss and accumulate dirt and grime. Dust can scratch and abrade the varnish and binder layers during handling. The solubilities of the collodion image layer and the varnish are typically very similar, and the collodion is very easily abraded, so it is likely that any attempt to remove a discolored varnish will also remove some image-carrying layer.
22.214.171.124 Paint/pigment components
Pigments may be applied to ambrotypes in several ways and using various binding media. If watercolors are used, these will require the addition of a suitable wetting agent, such as ox-gall. Paints may be applied over the image-carrying layer or behind the glass support. In the case of "flipped" plates, where the image is seen through the glass support, the hand-coloring applied to the image-carrying layer will be seen through the collodion silver image. Colorants are sensitive to light, moisture and abrasion. "Shell gold" (metal powder in oil or gum Arabic solution) was used to highlight selected image areas, such as buttons and jewelery.
Cased photographs are composite artifacts having complex reactions to environmental conditions. Conditions that are optimal or innocuous for one component may be damaging to another. Environmentally induced deterioration processes in one component may cause the production of reaction products harmful to another component.
Cycling temperatures may produce interlayer cleavage of weakly adhered layers due to differences in dimensional response. High temperatures may cause desiccation and may promote the deterioration of inherently unstable collodion layers, lacquer and varnish layers. Lower storage temperatures will retard deteriorative processes of paper components and collodion binders but will not dramatically benefit either the silver image or the glass support. There is no reason ambrotypes cannot be housed in RH-controlled low-temperature storage areas. (These facilities must be equipped with appropriate transition climates to avoid transitory high humidity conditions on removal to normal temperature areas.)
126.96.36.199 Relative humidity
In all types of cased objects, high relative humidity will contribute to deterioration of unstable glass, as well as corrosion of metal supports, mats and preservers. The leather, paper and wood components of cases will swell and shrink with fluctuating humidity, and they may become embrittled at low humidity. Leather may be structurally weakened at high humidity. Relative humidity above 60% can sustain mold growth. The major driving forces behind glass corrosion are moisture and fluctuations in relative humidity. Water (from moisture in the air) interacts on an atomic level with the glass surfaces, initiating glass corrosion cycles. Glass is best maintained at moderate relative humidity (40-50%) without excursions to higher or lower humidity. High humidity may accelerate the deterioration of the inherently unstable collodion layers of ambrotypes. For a mixed collection of ambrotypes, daguerreotypes and tintypes, 40% RH seems the best compromise condition. If possible, minimize the difference between the humidity conditions in the storage area and the areas where the objects are used for reference and display.
188.8.131.52 Environmental pollutants
Atmospheric pollutants can cause image deterioration in all types of cased objects. Sulphur dioxide, a common pollutant, can combine with oxygen and moisture to form sulphuric acid, which is particularly damaging to leather and paper. The silver image material of all cased photographs may be damaged by the ammonia, ozone, sulfur dioxide and nitrogen oxides generated in industrial environments. Sulphur and nitrogen compounds can cause deterioration of the collodion binder. (Most ambrotype plates are largely protected from contact with pollutants by the clear varnish layer.) Varnished ambrotype images that are well sealed and boxed will be relatively free from harm by airborne pollutants. However, the source of corrosion-inducing pollutants may be the materials composing the package and case. These should be removed or isolated from the image-carrying layer.
Silver image particles are generally not sensitive to light. However, as with all organic films, the collodion layer may be somewhat light sensitive. More seriously, light is damaging to the natural resin varnishes used on ambrotypes. The pigments used for hand-coloring and the textile components are frequently quite light sensitive.
184.108.40.206 Storage containers
Cased photographs may be stored flat inside Solander boxes equipped with Ethafoam layers cut out to create cavities in which the cases fit snugly. The interior surface of the cavity is lined with a fine unbleached cotton textile to provide a nonabrasive surface. Alternately, custom-made individual matboard boxes of the clamshell or slipcase variety may be constructed to house cased ambrotypes. A four-flap enclosure adapted for housing cased photographs is used at the Harry Ransom Humanities Research Center. (Brown, 1996) This method is well-adapted for storing cased photographs on their edges, a measure recommended by some conservators to reduce glass corrosion-induced damage on the plate surface. Note that the inclusion of paper or cardboard inside containers provides some buffering capacity to modulate humidity fluctuations. Appropriately conditioned silica gel-containing sheets may be useful inside sealed containers for establishing stable humidity conditions. Materials containing molecular sieves (zeolites) can absorb pollutants that might otherwise produce deterioration in photographs.
In the following section, it is assumed that all treatments will be carried out by qualified conservators familiar with the materials and characteristics of the objects they are treating. No treatment indications given here can be considered safe for any object without suitable spot testing, careful observations and skilled, judicious application.
220.127.116.11 Repair of broken plates
Ambrotypes with broken glass supports are difficult to repair for several reasons:
- adhesives appropriate for glass repair may be reactive with the image components of the ambrotypes;
- the edges to be mended require preparation with detergents or degreasing agents, which can have deleterious effects on image components;
- it may be difficult to align the broken pieces without damaging the image layer or the pigmented lacquer;
- repairs to broken glass supports are generally quite visible.
While there are several epoxy adhesives with a similar refractive index to that of glass, these are not generally suitable for ambrotype plate repair because accidental spread of the adhesive on the image layer during application cannot be safely removed. In addition, epoxies of this type generally have poor aging characteristics.
Acryloid B-72 is a methyl methacrylate polymer which has been used successfully to repair glass plate negatives. While the bond formed is relatively weak and there may still be problems with removing excess, this adhesive is nonyellowing and reversible. If the mend must be removed, this can be done by either warming the joint sufficiently to soften the adhesive or using a nonpolar solvent such as toluene.
The ideal adhesive for repairing broken ambrotype plates would use a cleanup solvent that does not interact with the image-carrying layer or coatings, would be reversible and nonyellowing, would form a strong bond with glass and would match the refractive index of glass. (A new consolidating resin, poly(2-ethyl-2 oxazoline), also called "Aquazol-50" or "P-Ox," should be tested in this application. See Wolbers; McGinn; Duerbeck. Painted Wood:
History and Conservation, Williamsburg, Va., Nov. 11-14, 1994, conference abstract, p. 40.) Until such an adhesive is available, conservators may choose to only stabilize broken ambrotypes with passive measures -- by placing them in secure housing such as a custom sink mat.
Dust may be removed from unvarnished collodion with a gentle stream of air from a rubber bulb syringe. These unprotected collodion surfaces are generally too fragile to tolerate any contact. Care should be taken not to dislodge the loosely bound hand-coloring. Varnished collodion that exhibits no signs of flaking or deterioration may be gently brushed to remove dust. Begin by brushing the glass surface with a long-haired soft brush while holding the plate firmly in one hand. Always brush from the center of the plate outward. This will reduce disturbance to damaged or abraded emulsion at the edges.
Ambrotype plates in good condition may sometimes be cleaned with water or organic solvents, although careful spot testing is imperative. Although immersion treatments have been reported, controlled application of cleaning solutions with cotton swabs or small brushes may be safer. Collodion and spirit varnishes are often soluble in alcohols and acetone. Deteriorated collodion may also be sensitive to water. Another consideration is the possible presence of an albumen substrate. If present, the albumen may absorb some water, causing the collodion emulsion to lift. Water may also cause blooming in the varnish layer. The presence of hand-coloring may be a further complication. This may have been applied to either the collodion image-carrying layer, underneath the varnish, or may be applied to the varnish surface. Alkaline solutions may alter the silver images of ambrotypes and should be avoided. Ketone and aromatic hydrocarbon solvents will risk solubilizing the varnish and collodion layers. Spot testing may establish that hexane, mineral spirits, naphtha, petroleum benzine, trichloroethylene or trichloroethane can be used.
18.104.22.168 Pigmented lacquer layer -- consolidation; inpainting losses
Any attempt at consolidation, inpainting or removal of the pigmented lacquer will be greatly complicated by the presence of an underlying collodion image-carrying layer and albumen sublayer. (See next Section.) Thus, it is important to determine if the lacquer has been applied directly to the collodion layer or is on the uncoated glass side of the support. Acryloid B-72 in xylene (15-20%) may be appropriate for consolidation of a lacquer layer adjacent to a collodion layer. (Two or three applications may be necessary to effect consolidation.) Heptane or petroleum benzine might also be tested as solvent vehicles for the consolidating resin. If the damaged lacquer layer is located on the uncoated glass side of the support, consolidation with a local application of an appropriate adhesive will be simpler. Likely candidates for this are Klucel G (hydroxypropyl cellulose) in alcohol or Acryloid B-72 in xylene. Another possibility for lacquer consolidation is the use of a solvent chamber to deliver solvent vapors. Testing the safety of such a procedure may be difficult. A backing of acrylic black velvet may be used to reintegrate missing sections of lacquer without having to remove original material. Alternatively, a backing of good-quality black paper (Arches Cover Black for example) along with an interlayer of Mylar Type D (3 or 5 mil) provides the high gloss and blackness necessary for this type of minimal-intervention reintegration. The lacquer is generally an original component of the object, and this must be a consideration in any decision to remove and replace it. However, if deterioration is so severe that complete removal is judged to be the best treatment option, the black layer may be replaced by velvet, paper/Mylar or by re-painting the glass surface with an appropriate paint. Small losses to the lacquer have been successfully inpainted with watercolor or with acrylic resin paints. Acrylic resins may be dispersed in heptane or petroleum benzine for this purpose. Reversibility and compatibility with the existing coating must be considered. (Refer to Photographic Materials Conservation Catalog, Chapter 4 -- "Inpainting of Historic Photographic Prints" for comments on specific inpainting materials.)
22.214.171.124 Collodion image-carrying layer -- consolidation
The thin collodion layer on an ambrotype, if it is found to be in poor, unstable condition, will be extremely difficult to successfully consolidate. The possible presence of an albumen sublayer further complicates the approach. The usual caution conservators exercise in approaching treatment options must be doubled in these instances. Careful spot testing is imperative before consolidation can be undertaken. Weak gelatin and methylcellulose solutions (applied with a brush) may be used to readhere flaking collodion to its underlying glass support. Alternatively, Acryloid B-72 in xylene may be used. It may be possible to disperse the acrylic resin in heptane or petroleum benzine for this purpose. One conservator has reported success using heat-activated PVA resin -- AYAF, 5% in ethanol. (Baas, 1982) In all cases, the application of consolidants should be considered irreversible. It may be possible to readhere flaking collodion with solvent vapor applied in a solvent chamber. Overall applications of varnish as a consolidation treatment are not recommended.
126.96.36.199 Collodion image-carrying layer -- inpainting losses
There is little published research concerning the inpainting of ambrotypes and tintypes. Dry pigments mixed with an acrylic resin, such as Acryloid B-72 (soluble in nonpolar solvents), have been successfully used to inpaint ambrotypes. Consider dissolving the resin in heptane or petroleum benzine for this application. Klucel G (hydroxypropyl cellulose) and Soluvar Matte Varnish have also been suggested as inpainting media. An appropriate isolating layer should be used beneath all inpainting. (Refer to Photographic Materials Conservation Catalog, Chapter 4 -- "Inpainting of Historic Photographic Prints" for comments on specific inpainting materials.) One contributor reports successful use of pastel dust applied without any vehicle using a very soft bristle brush. The pastel dust can be removed, if necessary, with a nonpolar solvent or by simply blowing it away.
188.8.131.52 Repackaging plates
See Section 184.108.40.206
See Section 220.127.116.11
2.5 Tintype Plates
Tintypes are direct positive photographs produced on a lacquered iron Usually both sides of the metal plate were coated with the black (or brown) pigmented lacquer (sometimes called "japanning" or "Japan varnish"). One side of the plate is subsequently coated with iodized collodion. The wet collodion layer is then sensitized, exposed and developed. Physically-developed silver particles form the image highlights; this image silver was made to appear lighter in color by using diluted developers, development retarding agents, whitening agents (such as mercuric chloride) or cyanide fixers. Against the dark lacquered plate, the image appears as a positive. After development, the collodion image is fixed, dried and varnished. Hand-coloring may be applied before varnishing. The images are laterally reversed. Multiple images of the same subject could be produced with a multiple-lens camera, such as a carte-de-visite camera. Tintypes may be cased, as with ambrotypes and daguerreotypes, but more commonly they are found completely unhoused or in a paper window mat. Tintypes are often found mounted in specially manufactured tintype albums. Small tintypes were sometimes mounted in jewelery. The tintype process and its variants were used well into the twentieth century. Later versions of the process used gelatin silver emulsions on both lacquered metal and black paper supports.
18.104.22.168 Iron Support
All types of metal supports are subject to mechanical distortion from bending or other mechanical working. The thin, flexible iron sheet of the tintype is particularly vulnerable to folding and bending, which frequently results in damage to overlying layers. Rust (iron oxide) is the most serious deterioration encountered on tintypes. This may occur at the edge of the plate, where the plate is more exposed to the environment. Alternately, cracks and losses in the pigmented lacquer, collodion and varnish layers caused by mechanical distortion and physical damage (scratches, folds and bends) result in exposure of the iron plate. Rust formation will lead, in turn, to further losses in the overlying layers. Note that rust, unlike other metal corrosion products, is generally not stable or protective against further corrosion. Dust can contribute to the corrosion of the iron support by retaining moisture and other corrosion initiators. A variant of iron corrosion is filiform corrosion that appears as irregular fine lines of corrosion products below the overlying layers. Tiny quantities of concentrated electrolyte solution formed by contaminants such as iron chlorides under the black lacquer layer move forward by capillary forces. This is generally seen as a series of raised trails under the image that are especially noticeable in raking light. The "head" of the trail is the site of active corrosion; it moves through the iron support, leaving behind a trail of corrosion products in its path. This type of corrosion appears active only in environments with relative humidity above 58%. Iron oxides are more transparent to X rays than is iron. This difference could be used to determine the extent of corrosion that has occurred under the image and lacquer layers.
22.214.171.124 Pigmented Lacquer Layer
The iron support of the tintype was coated (usually on both sides) with a black or brown lacquer that frequently contained a combination of linseed oil (or mastic or copal resin), asphaltum and pigment. This was baked onto the iron surface. Filiform corrosion may occur beneath this lacquer coating. The lampblack used in some coating formulations can promote corrosion of iron.
126.96.36.199 Collodion Image-carrying Layer
Collodion film is a form of cellulose nitrate produced from a solution of pyroxylin (cotton treated with mineral acids) dissolved in ether and alcohol. Collodion is soluble in many organic solvents. Collodion may be chemically unstable, particularly if excess alcohol was used in preparing the solution. These influences may result in collodion layer cracking or flaking. Collodion may yellow and become more opaque with age, causing a decrease in image contrast. Unvarnished collodion is extremely susceptible to mechanical abrasion.
188.8.131.52 Silver Image
The physically developed silver particles of tintypes are larger than the colloidal photolytic silver particles typical of printing-out processes. The silver images of tintypes, if properly processed, do not generally fade or discolor. However, tintypes may exhibit silver corrosion, particularly if the plate is unvarnished. Residual processing chemicals in the collodion layer, especially sodium thiosulfate, may cause staining and fading of the silver images.
184.108.40.206 Paint/pigment Components
Paints, usually watercolors and gouache, are applied on the tintype surface after treatment with a suitable wetting agent, such as ox-gall. Colorants are sensitive to light, moisture and abrasion. "Shell gold" (metal powder in oil or gum arabic solution) was used to highlight selected image areas, such as buttons and jewelery.
Clear varnishes were used as protective coatings for all photographs employing collodion image-carrying layers; white shellac, dammar, sandarac and copal were commonly used resins. The varnish saturates the image by increasing gloss, and protects the underlying collodion layer and its silver image from physical damage and chemical deterioration. Tintype varnishes are applied as "spirit varnishes" which have a small amount of varnish resin dissolved in a solvent. The varnish was flowed onto the tintype surface, forming a film considerably thinner than a brushed varnish. Varnishes may lose gloss, become discolored, develop crazing or flaking, or accumulate dirt and grime. Deteriorated varnish may damage or obscure the underlying image layer. The abrasive nature of dust can scratch the varnish layer during handling. Research has shown the collodion/varnish interface on tintypes to be an intermingled zone rather than a discrete separation. The solubilities of collodion and the varnishes are often very close, and the collodion is very easily abraded, so it is likely that any attempt to remove a discolored varnish would also damage the collodion image-carrying layer.
Heat alone is not a primary determinant of deterioration for tintypes. Cycling temperatures may produce interlayer cleavage of weakly adhered layers due to differences in dimensional response. High temperatures will accelerate deterioration of inherently unstable collodion and varnish layers. Additionally, high temperatures may lead to loss of moisture and desiccation of paper and case components. Lower storage temperatures will retard deteriorative processes of paper components and collodion binders but will not dramatically benefit either the silver image or the iron support. There is no reason tintypes cannot be housed in RH-controlled low-temperature storage areas. (These facilities must be equipped with appropriate transition climates to avoid transitory high humidity conditions on removal to normal temperature areas.)
220.127.116.11 Relative Humidity
Atmospheric moisture accelerates rust and filiform corrosion on the iron supports. High humidity may accelerate the deterioration of inherently unstable collodion. Tintypes without cases may benefit from storage conditions below 40% RH. For a mixed collection of tintypes and cased photographs, 40% RH seems the best compromise condition. If possible, minimize the difference between the humidity conditions in the storage area and the areas where the objects are used for reference and display.
18.104.22.168 Environmental Pollutants
Pollutants (especially sulfur and nitrogen compounds) can cause deterioration of the collodion silver images of tintypes, especially unvarnished plates. A varnished tintype that is well boxed will be relatively free from harm by airborne pollutants. However, the source of corrosion-inducing pollutants may be the original housing materials. These should be isolated from the plate, if possible.
Light is damaging to the natural resin varnishes used on tintypes. The pigments used for hand-coloring are frequently quite fugitive. The paper components of the packages may also be light-sensitive.
22.214.171.124 Storage Containers
Cased tintypes may be housed in custom-made boxes as described above for ambrotypes and daguerreotypes. Tintypes in original paper mats may be over-matted in high-quality matboard window mats and stored in print boxes. Unhoused tintypes may also be matted. One approach to securing the plate for matting is described in Section 126.96.36.199 below. Plates housed in this way can be fixed into a conventional window mat with a backboard and stored in a print box. For a large collection of uncased tintypes that have no original paper mats, a novel storage method has been suggested by contributors M. Fischer and A. Robb. This is an adaptation of a common technique used by archaeological conservators. Iron and other metals are kept in a low-relative-humidity environment by placing them in airtight food containers (such as Tupperware or Rubbermaid) containing preconditioned silica gel desiccant to control the relative humidity. This technique would be particularly useful for tintype collections kept in historic house museums that cannot maintain low relative humidity. This housing also has the benefit of isolating the collection from harmful atmospheric pollutants. Use a good-quality plastic container, such as one made of polyethylene that has passed the Photographic Activity Test. The amount of desiccant used is determined by the volume of the container. The silica gel is packed into polyester netting or a pierced polyethylene bag. A humidity indicator card should be placed in the box so that the relative humidity levels can be monitored. The quality of the seal of the container, the number of times the box is opened, and the ambient humidity when the box is sealed will all effect the period before reconditioning of the silica gel is necessary. While this storage technique has not been tested, it shows promise and warrants testing.
188.8.131.52 Handling Mat for Tintypes
Outline the exact shape of the plate at the center of two sheets of high-quality 2-ply matboard that are approximately three times the height and width of the plate. Cutting freehand, create bevel apertures in both sheets that follow the plate outlines precisely; the bevel should be exaggerated to provide a lip that will catch and hold the plate in a channel between the two sheets, as in the diagram on the previous page. Use 3M Double-sided Tape No. 415 to firmly attach the cardboard sheets together, creating a tight channel in which the perimeter of the tintype plate is held. These units can be stored in boxes or be individually enveloped. For display, they can be hinged into a conventional 4-ply window mat and framed.
184.108.40.206 Plastic Sleeves for Tintypes
Unprotected tintype plates or plates mounted in decorative paper mats may be inserted into a plastic sleeve with a high-quality 2-ply matboard insert as a stiffener and a humidity buffer. Polyester, polyethylene and polypropylene are suitable plastics. Plates with flaking collodion binder or friable hand-coloring media should not be put in plastic sleeves. The use of food-grade polyethylene "zip-lock" bags may be considered as an inexpensive and effective protective container for tintypes. Appropriate tests should be carried out on the specific product used. Sheet-form silica gel might be included as a desiccant.
In the following section, it is assumed that all treatments will be carried out by qualified conservators familiar with the materials and characteristics of the objects they are treating. No treatment indications given here can be considered safe for any object without suitable spot testing, careful observations and skilled, judicious application.
Some conservators have found that it is possible to flatten bent tintypes by burnishing the reverse with a smooth tool. Care must be taken to protect both front and reverse surfaces, perhaps with polyester film. Other conservators have successfully reduced the distortions of badly bent plates in a press, first sandwiching the plate between sheets of polypropylene and many layers of blotter; no visible damages were noted in the overlying layers when observed under magnification. However, it may be that overlying varnish and collodion layers are weak or cracked in these bent areas; flattening the tintype may exacerbate the damage. Contributors M. Fischer and A. Robb, while testing various treatments suggested for tintypes, found that flattening generally led to damage in the binder layer due to its extreme brittleness at room temperature. Their testing found that heating to increase the flexibility of the varnish layer during flattening does not greatly aid in the procedure. They found burnishing to not be particularly effective and to cause abrasions on the image layer. Planar deformations can be left untreated and the (distorted) plate can be supported in a custom sink mat housing.
220.127.116.11 Iron Support - Reduction of Rust
"Rusted iron seems to be the worst possible thing conservators encounter." (Brown et al., p. 137) Unlike other corrosion products, rust does not serve as a protective barrier for the uncorroded iron beneath it. Corrosion occurs in areas exposed due to damage, along the exposed edge of the plate, and even under the black lacquer layer itself producing blind cleavage. In treating iron corrosion, it is imperative to reduce the quantity of accumulated rust to a minimum before proceeding with any passivation, consolidation or coating steps. The removal or isolation of chloride contaminants is especially important since iron chloride is hygroscopic and produces a self-catalysed corrosion action. Chloride-induced corrosion is recognizable by its bright orange color. The presence of chlorides lowers the relative humidity threshold necessary for active corrosion from 60% to 40%. The only suitable technique for rust reduction on tintype supports is mechanical removal with small instruments. (Rust reduction with enzyme agents and complexing agents has been reported, and may eventually prove useful in the treatment of rusted tintypes.) General problems with mechanical reduction include the fact that it will not remove all the rust and may also cause the loss of flaking sections of the collodion image-carrying layer. In addition, mechanical removal of rust exposes uncorroded iron that must now be protected from further corrosion. The newly exposed iron is also quite shiny and may have to be treated in some way to make it less obvious. Fischer and Robb experimented with several mechanical instruments. They tested a scalpel blade and a micro-spatula on rust in an area of image loss; these resulted in evident scratches and removal was incomplete on a microscopic level. A softer material, such as a sharpened hardwood stick, resulted in incomplete rust removal but did not leave evident scratches.
18.104.22.168 Iron Support - Passivation
The following section contains commentary and results derived from preliminary research on possible treatment options for tintypes carried out by contributors M. Fischer and A. Robb in 1992. None of the measures considered are current conservation treatment practices; they are offered here as a means of disseminating possible ideas for further research and testing. Passivation is the production of an inert surface on a metal object that will not corrode in the future. One approach to iron passivation uses tannic acid. The treated area darkens to a black color a day or two after application. Preparation of the surface requires that the area be degreased and stripped -- difficult procedures due to the solubilities of the binder and varnish layers. The tannin must be used in an acidic solution (pH 2-3). Once the iron-tannate complex is formed, a coating should be applied. Proper equipment/protection must be in place when using tannic acid, a suspected carcinogen. (See Logan or Pelikán.) Pyrogallol (1,2,3-benzenetriol; 1,2,3-trihydroxybenzene; pyrogallic acid) can be used to form a protective blue/black pyrogallate layer on iron, similar in color to the lacquer. Care should be taken when using pyrogallol as the Merck Index considers it a poisonous substance. Two solutions of pyrogallol were tested by Fischer and Robb, one in water, the other in ethanol. The solvent carrier may cause problems to either the metal base, the lacquer or to the collodion binder layers. The method showed promising results; further testing of the material and technique is warranted. Rust-Oleum Rust Reformer is a commercial product made by the Rust-Oleum Corporation of Vernon Hills, Illinois and is available in hardware stores. It consists of tannic acid in a water-based vinyl acrylic copolymer emulsion with diethylene glycol methyl ether. The addition of the vinyl acrylic copolymer appears to act as a consolidant and a glossing agent. This combination of corrosion reduction and consolidant in one step may not be desirable; the action of tannic acid may be incomplete due to the premature drying of the consolidant. This appears to have been the cause of blistering in surface coating testing on aged samples. First, the areas of corrosion must be reduced as much as possible; the product can then be applied sparingly to areas of active corrosion. The result is a glossy black that resembles tintype lacquer. If not applied carefully, an excess could be left on the image layer. Testing of this product by Fischer and Robb gave very good results but long-term effects are not known; further investigation is warranted. Vapor phase inhibitors (VPIs) are compounds that invisibly coat the surface of a metal, excluding moisture and thus acting as a barrier. They require specific conditions to work, and little is known as to their effects on photographic images. Further testing may show them to be useful. One specific vapor phase inhibitor mentioned in Davis (p.18) that warranted testing was Daubert VCI, a paper impregnated with dicyclohexylammonium nitrate.
22.214.171.124 Iron Support - Consolidation/coating
The following section contains commentary and results derived from preliminary research on possible treatment options for tintypes carried out by contributors M. Fischer and A. Robb in 1992. None of the measures considered are current conservation treatment practices; they are offered here as a means of disseminating possible ideas for further research and testing. Since the entire iron support cannot be treated, corrosion reduction, passivation, consolidation, and coating treatments cannot fully stabilize the rusting tintype. They are really only local cosmetic treatments. Given this limitation, as well as the problematic nature of the materials used (solvents, water, heat), these consolidation treatments should be undertaken only after careful consideration. Rust reduction must be done before any attempt at consolidation, since corrosion products should not be trapped under the consolidant layer. The extent of the risks involved in using solvents, water and heat on tintypes is unresolved. It is important to dry and degrease a metal surface before coating. Heptane may be an acceptable degreasing agent. The use of gentle heating (under 40o C) may be an acceptable drying treatment, although this may be problematic due to the differing thermal coefficients of expansion of the tintype layers. Surface gloss factors may have to be considered when choosing a consolidant. Other critical factors may include aging characteristics and flexibility/strength of the consolidant. Consolidants used by metals conservators on corroding objects include waxes, natural lacquers and synthetic products. Among waxes, microcrystalline wax is better than paraffin due to its superior water impermeability. Application of wax to a tintype may be difficult, especially in the delivery and the removal of any excess. Polyvinyl acetate and acrylic resins in various solvents were tested by Fischer and Robb as consolidants/coatings on a group of tintypes. Factors such as gloss, solubility of tintype components and degree of control were examined.
- Polyvinyl acetate resins
- AYAT, 10% in toluene -- this gave the glossiest appearance.
- AYAF, 5% in ethanol -- severely flaking collodion emulsion may be locally consolidated with this solution; care must be taken as the collodion binder is soluble in ethanol.
- Acrylic resins
- Harder resins:
- Acryloid B-48N, both 10% and 20% (w/v) in xylene/ethanol (1/1) were investigated as consolidants; both mixtures gave a matte appearance and worked well as consolidants.
- Intermediate hardness resins:
- Acryloid B-67, 20% (w/v) in petroleum benzine gave a glossy surface, but not as shiny as that produced by the 10% AYAT in ethanol.
- Acryloid B-72; this resin was not tested.
- Acryloid B-82; this resin was not tested.
- Softer resins:
- Acryloid F-10, 10% (w/v) in petroleum benzine gave a matte appearance and seemed to work well as a consolidant. Consider that it is softer than the others tested and may not give the strength needed.
- Harder resins:
Those consolidants dissolved in ethanol or part ethanol flowed more rapidly and easily, which allowed less control. Consolidants in toluene flowed most slowly, making the application more manageable.
One source recommends applying graphite to the coated surface to form another protective layer that excludes moisture.
The materials noted above should serve as a guideline to what is available and how they might be used on tintypes. No particular polyvinyl acetate or acrylic resin can be singled out as a panacea for treatment.
126.96.36.199 Surface Dusting
Dry cleaning is important because it can reduce dirt and grime while avoiding the problems associated with wet cleaning. However, reduction of dust and grime is problematic due to the potential of scratching the varnish and/or binder layers by the action of the dust or the device used to remove the dust. Flaking and cracked binder and varnish layers further complicate dry cleaning. While brushing, apply pressure sparingly. Sometimes the electrostatic charge from the brush alone is enough to pick up any dust particles in sensitive areas. Brushing may not remove all of the imbedded dirt and grime. Squirrel-hair brushes are among the softest western brushes. They are softer than cotton swabs and are not very resilient. A less resilient brush may be desirable when working in sensitive flaking areas. Different shapes and sizes of brushes should be considered. When working with the brushes, one should work from the middle outwards. When working near cracks and flaking areas, hold the brush perpendicular to the damaged area to reduce any chance of contact. It may be advisable to work under a microscope when dealing with severely flaking tintypes. Fischer and Robb experimented with the use of erasers and eraser crumbs; they do not recommend their use for dry cleaning of tintypes. They also experimented with cotton swabs, aspirators and blowers; they felt these provided less control than brush cleaning.
188.8.131.52 Surface Cleaning
Cleaning with organic solvents or aqueous solutions has the potential to remove embedded dirt and grime that cannot be removed by dusting. However, the potential for damaging the tintype is greatly increased in comparison to dusting; the varnish, collodion binder and iron support might all be damaged. Water contributes to the corrosion of the iron support. Many organic solvents will solubilize the varnish, the collodion binder or both. Note that tintypes were made in different ways by varying methods and materials, and that this variability makes any generalization concerning their solubility characteristics The issue of whether surface cleaning of a tintype with solvents or aqueous solutions should be attempted is unresolved. McCabe (1991) states that "Washing collodion plates can be very damaging and should not be attempted." Fischer and Robb also discourage cleaning with either organic or aqueous solvents. The choice of delivery method for the cleaning agent is another complicating factor in wet cleaning. Despite their abrasiveness, cotton swabs are most commonly used because of the swab's ability to pick up and retain dirt. The abrasive nature of cotton in this context cannot be understated. Often the swelling action of the cleaning solution can make the varnish and/or collodion surface more sensitive to abrasion. Fischer and Robb also observed that dark areas (that is, nonsilver areas) are especially sensitive to abrasion. Fischer and Robb have tested the following solvents and solvent mixtures for liquid cleaning of tintypes: water, ethanol, water/ethanol (1/1), water/ethanol (25/75), petroleum benzine, heptane, acetone, xylene, and toluene. It would appear from their testing that ketone and aromatic hydrocarbon solvents should be avoided. Water did not appear to harm these layers, but its use is problematic as far as the iron support is concerned. Alcohols and short-chained aliphatic hydrocarbons may have less effect on varnish and collodion layers but can still cause damage if wrongly applied or applied to sensitive areas. (Naphtha should be included in solvent testing.)
184.108.40.206 Pigmented Lacquer Layer - Consolidation; Inpainting Losses
See Ambrotype treatment, Section 220.127.116.11.
18.104.22.168 Collodion Image-carrying Layer - Consolidation
See Ambrotype treatment, Section 22.214.171.124.
126.96.36.199 Collodion Image-carrying Layer - Inpainting Losses
See Ambrotype treatment, Section 188.8.131.52.
- Alabastrine process -- a variant of the ambrotype process, using mercury chloride bleaching
- Ambrotype -- a collodion silver photograph on glass; a direct positive camera original
- Amphitype -- among other things, a process similar to ambrotype but using albumen
- Binding tape -- an alternate term for sealing tape
- Case -- a hinged box holding an ambrotype, or an American or British daguerreotype
- Clasp -- brass hardware on a case that secures the closure of the hinged case cover
- Collodion -- binder layer of ambrotypes, tintypes, and wet-plate negatives
- Collodion positive -- term used in Britain for ambrotype
- Cover glass -- protective glazing used on daguerreotypes, and some ambrotypes and tintypes
- Cushion -- cardboard, cotton fibre and textile pad fixed to the inside surface of the case cover
- Daguerreotype -- a photograph with silver image particles on a silvered copper plate
- Deliminator -- an alternate term for a metal mat
- Ferrotype -- an alternate term for tintype
- Gilding -- a step in daguerreotype processing in which gold is added to the image particles
- Hinge -- paper, leather or metal attachment between the case cover and tray
- Lacquer -- a pigmented paint layer, used on both ambrotypes and tintypes
- Lampratype -- a variant of the ambrotype process
- Mat -- paper or metal sheet with an aperture cut in its centre
- Melainotype, melanotype -- alternate terms for both ambrotype and tintype
- Package -- plate and housing components forming a sealed unit; may be cased or framed
- Pad -- an alternate term for cushion
- Pannotype -- a collodion positive, similar to a tintype, but on black waxed textile or leather
- Passe-partout (package) -- a daguerreotype housing format common in Europe
- Perfling -- an alternate term for retainer
- Pinchback -- an alternate term for preserver
- Pinch pad -- an alternate term for retainer
- Preserver -- for cased objects: brass foil that is folded around the edges of the plate package
- Relievo -- a variant of the ambrotype, in which the background image areas are scraped away
- Retainer -- velvet and cardboard strip lining the edge of the case tray
- Sealing tape -- strip adhered at the perimeter of a package and holding the components together
- Stereograph -- a two-image photograph which represents its subject three-dimensionally
- Tintype -- a collodion silver photograph on an iron plate; a direct positive camera original
- Tray -- the half of the case opposite the cover, which receives the package
- Union case -- a case made of an early thermoplastic material
- Angelucci, S.; P. Florentino; J. Kosinkova; M. Marabelli. "Pitting Corrosion in Copper and Copper Alloys: Comparative Treatment Tests." Studies in Conservation 23 (1978), pp. 147-156.
- Austin, Michele C. "An Examination of Daguerreotype Brass Mats." University of Delaware/Winterthur Art Conservation Program, unpublished student research project report, 21 May, 1984.
- Barger, M. Susan; Deane K. Smith; William B.White. "Characterization of Corrosion Products on Old Protective Glass, Especially Daguerreotype Cover Glasses." Journal of Materials Science 24 (1989), pp. 1343-1356.
- Brown, Barbara. "Four-flap Enclosure ('Tuxedo' Case) Adapted for Housing Cased Photographs." Austin, Texas: Harry Ransom Humanities Research Center, unpublished presentation, September 1996.
- Hendriks, Klaus B.; Brian Thurgood; Joe Iraci; Greg Hill. Fundamentals of Photograph Conservation: A Study Guide. Toronto: Lugus Publications, 1991.
- Hendriks, Klaus B. CCI Notes 16/1: Care of Encased Photographic Images. Ottawa: Canadian Conservation Institute, 1995.
- Hill, Jo. "Corrosion of Mats and Preservers on Case Objects." University of Delaware/Winterthur Art Conservation Program, unpublished student research project report, May 1991.
- King, Chris. "My Grandmother Has One of Those -- Daguerreotypes, Ambrotypes, Tintypes -- Their Problems, Processes, and Care." Conference of Students in Art Conservation. April 10-12, 1978. Cooperstown, NY: Cooperstown Graduate Programs, 1978, pp. 82-97.
- Krainik, Clifford; Michele Krainik; Carl Walvoord. Union Cases: A Collector's Guide to the Art of America's First Plastics. Grantsburg, WI: Centennial Photo Service, 1988.
- Kusnerz, P.A. "Preservation of Case Photographs." Michigan Museums Review 7, no.4 (1973), pp.7-9.
- Longford, Nicola. "Stamped Vines and Verdigris: Uncasing the Mysteries of the Brass Mat." St. Louis: Missouri Historical Society, unpublished presentation, September 1996.
- Rempel, Siegfried. "The Conservation of Case Photographs." Archivaria no. 3 (winter, 1976/1977), pp. 103-108.
- Rinhart, Floyd; Marion Rinhart. "Miniature Cases for Daguerreian Art." In American Daguerreian Art. New York: Clarkson N. Potter, Inc., 1967, pp. 87-91.
- Rinhart, Floyd; Marion Rinhart. American Miniature Case Art. Cranbury, NJ: A. S. Barnes and Co., 1969.
- Smith, Brenda Lee. "Photographic Union Cases: The First Plastic Composite." Queen's University Art Conservation Program, unpublished student research report, 1994.
- Barger, M. Susan; S.V. Krishnaswamy; R. Messier. "The Cleaning of Daguerreotypes: Comparison of Cleaning Methods." Journal of the American Institute for Conservation 22 (1982), pp. 13-24.
- Barger, M. Susan; S.V. Krishnaswamy; R. Messier. "The Cleaning of Daguerreotypes: I. Physical Sputter Cleaning, A New Technique." AIC Preprints. Washington, DC: American Institute for Conservation of Historic and Artistic Works, 1982, pp. 9-20.
- Barger, M. Susan; R. Messier; William B.White. "A Physical Model for the Daguerreotype." Photographic Science and Engineering 26, no. 6 (1982), pp. 285-291.
- Barger, M. Susan. "Robert Cornelius and the Science of Daguerreotypy." In William F.Stapp. Robert Cornelius: Portraits from the Dawn of Photography. Washington, DC: The National Portrait Gallery, 1983, pp. 111-128
- Barger, M. Susan; R. Messier; William B.White. "Gilding and Sealing Daguerreotypes." Photographic Science and Engineering 27, no. 4 (July/August 1983), pp. 141-146.
- Barger, M. Susan; R. Messier; W.B.White. "Daguerreotype Display." Picturescope 31, no. 2 (summer 1983), pp. 57-58.
- Barger, M.Susan; A.P.Giri; William B.White; William S. Ginnell; Frank Preusser. "Protective Surface Coatings for Daguerreotypes." Journal of the American Institute for Conservation 24 (1984), pp. 40-52.
- Barger, M. Susan; Russell Messier; William B.White. "Nondestructive Assessment of Daguerreotype Image Quality by Diffuse Reflectance Spectroscopy." Studies in Conservation 29 (1984), pp. 84-86.
- Barger, M. Susan; William F. Stapp. "Daguerreotype: A Precautionary Discussion of Deterioration, Cleaning and Treatment." Preprints. ICOM Committee for Conservation Triennial Meeting, Copenhagen, 1984, pp. 84.14.8 - 84.14.12.
- Barger, M. Susan; William B.White. "The Optical Characterization of the Daguerreotype." Photographic Science and Engineering 28, no. 4 (July/August 1984), pp. 172-174.
- Barger, M. Susan; A. P. Giri; W. B.White; T. M. Edmondson. "Daguerreotype Cleaning." Studies in Conservation 31 (1986), pp. 15-28; and "Corrigenda." Studies in Conservation 32 (1987), pp. 141-143.
- Barger, M. Susan. "Delicate and Complicated Operations: The Scientific Examination of the Daguerreotype." In John A.Wood, ed., The Daguerreotype: A Sesquicentennial Celebration. Iowa City: University of Iowa Press, 1989, pp. 97-109.
- Barger, M. Susan. "Daguerreotype Care for the Collector." The Daguerreian Annual 2 (1991), pp. 27-32.
- Barger, M. Susan; William B.White. The Daguerreotype: Nineteenth-Century Technology and Modern Science. Washington, DC: Smithsonian Institution Press, 1991. (This is a fairly complete summary of most of Susan Barger's research on daguerreotypes to 1991.)
- Bisbee, A. The History and Practice of Daguerreotyping,--. First published, Dayton: L. F. Claflin, 1853. Reprinted, New York: Arno Press, 1973.
- Boudreau, Joseph. "Color Daguerreotypes: Hillotypes Recreated." In Ostroff, Eugene, ed. Pioneers of Photography, --. Springfield, VA: SPSE - Society for Imaging Science and Technology, 1987, pp. 168, 189-199.
- Brodie, I.; M. Thackray. "Photocharging of Silver Iodide and Its Relevance to the Daguerre Photographic Process." Nature 312, no. 5996 (20-27 December, 1984), pp. 744-746.
- Buerger, Janet E. French Daguerreotypes. Chicago: University of Chicago Press, 1989.
- Daffner, Lee Ann; Dan Kushel; John M. Messinger II. "Investigation of a Surface Tarnish Found on 19th-Century Daguerreotype." Journal of the American Institute for Conservation 35 (1996), pp. 9-21.
- Daguerre, (L. J. M.) "Practical Description of the Process Called the Daguerreotype --" Translated by J. F. Frazer. Journal of the Franklin Institute 24 (1839), pp. 303-311.
- The Daguerreian Annual --. Lake Charles, LA.: The Daguerreian Society, 1990 - .
- The Daguerreian Society Newsletter --. Green Bay, WI.: The Daguerreian Society.
- Daniels, V. "Plasma Reduction of Silver Tarnish on Daguerreotypes." Studies in Conservation 26, no. 2 (1981), pp. 45-49.
- Daniels, Vincent. "Advances in the Use of Hydrogen Plasma for Reduction of Silver Tarnish. Treatment of Daguerreotypes." Preprints. 6th Triennial Meeting, Ottawa, 1981. Paris: International Council of Museums Committee for Conservation, 1981, pp. 81/14/20-1 - 81/14/20-5.
- Edmondson, Thomas M.; M. Susan Barger. "The Examination, Surface Analysis, and Retreatment of Eight Daguerreotypes which were Thiourea Cleaned in 1977." Topics in Photographic Preservation 5 (1993), pp. 14-26.
- Enyeart, James L. "Reviving a Daguerreotype." The Photographic Journal 110 (September 1970), pp. 338-344.
- Hardwich, T. Frederick. "On the Theory of the Daguerreotype and Talbotype Processes, Etc." In A Manual of Photographic Chemistry, --. 4th ed. New York: S. D. Humphrey, 1858.
- Heller, Nancy Joan. "Electrocleaning of Daguerreotypes: Is Metallic Redeposition a Concern?" University of Delaware/Winterthur Art Conservation Program, unpublished student research report, 1988.
- Hill, Levi L.; W. McCartey. A Treatise on Daguerreotype,--. Reprint of the 1850 ed. New York: Arno Press, 1973.
- Hill, Levi L. A Treatise on Heliochromy:--. New York: Robinson and Caswell, 1856.
- Humphrey, S. D. American Handbook of the Daguerreotype,--. First published, New York: S.D.Humphrey, 1858. Reprinted, New York: Arno Press, 1973.
- Jacobson, Leon; W. E. Leyshon. "The Daguerrian Measles Mystery." Graphic Antiquarian 3, no. 4 (April 1974), pp. 14-15.
- Kempe, Fritz. Daguerreotypie in Deutschland: vom Charme d. fruhen Fotogr. Seebruck am Chiemsee: Heering, 1979.
- Koch, Mogens S.; Anker Sjøgren. Treatment of Daguerreotypes with Hydrogen Plasma. Copenhagen: Konservatorskolen Det Kongelige Danske Kunstakademi, 1984. (translation of, "Behandlung von Daguerreotypien mit Wassertoffplasma." Maltechnik Restauro 90, no. 4 (October 1984), pp. 58-64.
- McElhone, John P. "Restoration and Conservation of the Lambert Gift Collection of Daguerreotypes." Topics in Photographic Preservation 3 (1989), pp. 22-27.
- Monnier, Jérôme. "Mise au point d'un protocole de traitement de nettoyage des daguerréotypes non coloriés." Conservation-Restauration des Biens Culturels 6 (1994), pp. 37-39.
- Mustardo, Peter J. "The Daguerreotype's Environment." Topics in Photographic Preservation 1 (1986), pp. 16-22.
- Newhall, Beaumont. "A Technique and a Craft: The American Process." The Daguerreotype in America. New York: Duell, Sloan and Pearce, 1961, pp. 115-136.
- Norris, Debbie Hess. "Daguerreotype." University of Delaware/Winterthur Art Conservation Program, unpublished class notes, 1989.
- Pobboravsky, Irving. Study of Iodized Daguerreotype Plates. Rochester, N.Y.: Rochester Institute of Technology, 1971.
- Pobboravsky, Irving. "Daguerreotype Preservation: The Problems of Tarnish Removal." Technology and Conservation 3, no. 2 (1978), pp. 40-45.
- Ravenswaay, Charles van. "An Improved Method for the Restoration of Daguerreotypes." Image 5, no. 7 (September 1956), pp. 156-159.
- Rempel, Siegfried. "Recent Investigations on the Cleaning of Daguerreotypes." AIC Preprints. Washington, DC: American Institute for Conservation of Historic and Artistic Works, 1980, pp. 99-105.
- Rinhart, Floyd; Marion Rinhart. "Notes on the Daguerreotype Plate." The New Daguerrian Journal 3, no. 2 (1975), pp. 4-7.
- Rinhart, Floyd; Marion Rinhart. The American Daguerreotype. Athens, GA: University of Georgia Press, 1981.
- Romer, Grant B. "Some Notes on the Past, Present and Future of Photographic Preservation." Image 27, no. 4 (1984), pp. 16-23.
- Shoemaker, W. L. "Cleaning the Daguerreotype." The Philadelphia Photographer 14 (1877), p. 233.
- Sobieszek, Robert A., ed., The Daguerreotype Process: Three Treatises, 1840-1849. New York: Arno Press, 1973. (Reprints texts by Gouraud, 1840; Claudet, 1849; Humphrey and Finley, 1849.)
- Swan, Alice. "Conservation Treatments for Photographs. A Review of Some of the Problems, Literature and Practices." Image 21, no. 2 (1978), pp. 24-31.
- Swan, Alice. "The Preservation of Daguerreotypes." In AIC Preprints. Washington, DC: American Institute for Conservation of Historic and Artistic Works, 1981, pp. 164-172.
- Swan, Alice. "Coloriage des Epreuves: French Methods and Materials for Coloring Daguerreotypes." In Janet E. Buerger. French Daguerreotypes. Chicago: University of Chicago Press, 1989, pp. 150-163.
- Swan, A.; C. E. Fiori; K. F. J. Heinrich. "Daguerreotypes: A Study of the Plates and the Process." Scanning Electron Microscopy. AMF O'Hare, IL: SEM Inc., 1979, pp. 411-423.
- Wagner, Sarah S. "Some Recent Photographic Preservation Activities at The Library of Congress." Topics in Photographic Preservation 4 (1991), pp. 136-149 (see "Daguerreotype Project Preservation", pp. 143-145).
- Waters, Dennis A. "Copying Your Daguerreotypes: A Primer." The Daguerreian Annual 2 (1991), pp. 123-130.
- Watson, Roger C. "Preservation of Daguerreotypes." In Daguerreotype Workbook. Rochester: George Eastman House / International Museum of Photography and Film, 1996.
2.7.3 Ambrotypes and Tintypes
- Archer, Frederick Scott. "On the Use of Collodion in Photography." The Chemist 2 (March 1851), pp. 257-258.
- Baas, Valerie. "Conservation of Tintypes." American Institute for Conservation - Photographic Materials Group, 2nd annual meeting, Milwaukee, 1982, unpublished presentation.
- Baas, Valerie. "The Treatment of a Flood Damaged Ambrotype." American Institute for Conservation -- Photographic Materials Group, 3rd annual meeting, Chicago, February, 1983, unpublished presentation.
- Barger, M. Susan. "Characterization of Deterioration of Glass Supported Photographic Images." Printing of Transcript Summaries. Second International Symposium: The Stability and Preservation of Photographic Images. Springfield, VA: Society of Photographic Scientists and Engineers, 1985, pp. 134-147.
- Barger, M. Susan. "Deterioration of Glass-supported Photographic Materials." New Directions in Paper Conservation: IPC Tenth Anniversary Conference. Oxford: The Institute of Paper Conservation, 1986, pp. D132-D133.
- Brown, Floyd B.; Harry C. Burnett; W. Thomas Chase, et al. Corrosion and Metal Artifacts -- A Dialogue Between Conservators and Archaeologists and Corrosion Scientists (NBS Special Publication No. 476). Washington, DC: National Bureau of Standards, 1977.
- Burgess, Nathan G. The Ambrotype Manual. New York: Daniel Burgess and Son, 1856.
- Davis, Nancy. "Tintypes: Preliminary Research and Testing." Art Conservation Training Programs Conference, May 1-3, 1983. Cooperstown, NY: State University College of New York at Buffalo, 1983, pp. 13-28.
- Estabrooke, Edward M. The Ferrotype and How to Make It,--. First published, Cincinnati: Gatchel and Hyat, 1872. Reprinted, Hastings-on-Hudson, NY: Morgan and Morgan Inc., 1972.
- Feldvebel, Thomas P. The Ambrotype, Old and New. Rochester: Graphic Arts Research Centre, 1980.
- Fischer, Monique C.; Andrew O. Robb. "Treatment of Collodion on Metal (Tintype)." University of Delaware/Winterthur Art Conservation Program, unpublished student research report, 1992.
- Hannavy, John. "The Magnificent Ambrotypes." The British Journal of Photography (20 February, 1976), pp. 153-155.
- Heighway, W. "The Ferrotype." The Practical Photographer 3, no. 7 (1879), pp. 686-688.
- Humphrey, Samuel D. A Practical Manual of the Collodion Process, Giving in Detail a Method for Producing Positive and Negative Pictures on Glass and Paper. New York: Humphrey's Journal Printer, 1857.
- "Lessons on Colouring Photographs: Colouring Positives on Glass." The Photographic News 1 (November 26, 1858), p.138, et seq.
- Logan, Judy. CCI Notes 9/5: Tannic Acid Treatment. Ottawa: Canadian Conservation Institute, 1989.
- "The Lowly Tintype." The British Journal of Photography (26 December, 1975), pp. 1168-1170.
- Maurice, Philippe. "History, Identification, Deterioration Characteristics and the Preventive Care of Collodion and of Gelatin-emulsion Ferrotypes." Abstract, Environnement et conservation de l'écrit, de l'image et du son. Actes . . . 16-20 mai 1994. Paris: Association pour la Recherche Scientifique sur les Arts Graphiques, 1994, pp. 254-255.
- McCabe, Constance. "Preservation of 19th-Century Negatives in the National Archives." Journal of the American Institute for Conservation 30, no. 1 (Spring 1991), pp. 41-73.
- McCormick-Goodhart, Mark. "Research on Collodion Glass Plate Negatives: Coating Thickness and FTIR Identification of Varnishes." Topics in Photographic Preservation 3 (1989), pp. 135-150.
- McCormick-Goodhart, Mark. "The Multilayer Structure of Tintypes." In 9th Triennial Meeting, Dresden, German Democratic Republic, 26-31 August, 1990: Preprints. Volume 1. Los Angeles: International Council of Museums, Committee for Conservation, 1990, pp. 262-267.
- McCormick-Goodhart, Mark H. "An Analysis of Image Deterioration in Wet-Plate Negatives from the Mathew Brady Studios." Journal of Imaging Science and Technology 36, no. 3 (1992), pp. 297-305.
- McCormick-Goodhart, Mark H. "Glass Corrosion and its Relation to Image Deterioration in Collodion Wet-Plate Negatives." In The Imperfect Image: Photographs, Their Past, Present and Future. Conference proceedings. London: The Centre for Photographic Preservation, 1992, pp. 256-265.
- Moor, Ian. "The Ambrotype -- Research into Its Restoration and Conservation -- Part 1." The Paper Conservator 1 (1976), pp. 22-25; ". . . -- Part 2." The Paper Conservator 2 (1977), pp. 36-43.
- Newhall, Beaumont. "Ambrotype: A Short and Unsuccessful Career." Image 7, no. 8 (October 1958), pp. 171-177.
- Norris, Debbie Hess. "Ambrotype." University of Delaware/Winterthur Art Conservation Program, unpublished class notes, 1989.
- Norris, Debbie Hess. "Tintype." University of Delaware/Winterthur Art Conservation Program, unpublished class notes, 1989.
- Pelikán, J. B. "Conservation of Iron with Tannin." Studies in Conservation 11, no. 3 (August 1966), pp. 109-114.
- Peyton, Michael. "Tintype and Its Treatment." University of Delaware/Winterthur Art Conservation Program, unpublished student research project, May 1991.
- Trask, Albion K. P. Trask's Practical Ferrotyper. First published, Philadelphia: Beuerman and Wilson, 1872. Reprinted in Sobieszek, Robert A., The Collodion Process and the Ferrotype: Three Accounts, 1854-1872. New York: Arno Press, 1973.