PMG Resin Coated (RC) Papers History and Conservation

Photographic Material

Photographic Materials Group

Deterioration Issues
Materials
Supports
Surface
Tools, Equipment, Materials, and Supplies

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Page Information
Date initiated	Febraury 2025
Page Compiler	Zachary Long
Contributors	Luisa Casella

Definition and Terminology[edit | edit source]

Resin-coated (RC) photographic paper refers to a support material in which the paper base is coated with two thin layers of polyethylene (PE). The top layer of polyethylene, which will receive the photographic emulsion, is pigmented white, while the layer on the back of the support is kept clear. The effect of these coatings is to make the paper nearly water proof. Introduced commercially in the 1960s, RC paper rapidly became the dominant support for black-and-white and color photographic prints in both professional and consumer markets. By the mid-1970s nearly all of the chromogenic color papers manufactured had a RC support. By the late 20th century, billions of RC prints had been produced worldwide.

RC prints have several practical advantages that make them particularly advantageous to photo finishing labs:

Dimensional stability: The water-resistant nature of RC paper minimizes curling, cockling, and expansion/contraction during processing and drying. Manufacturers could also counteract curl from the gelatin emulsion responding to moisture by applying a higher density polyethylene to the back of the paper support.
Reduced solution carryover: RC papers absorb significantly less of the processing solutions than fiber-based papers, which in turn means less solution carryover between processing tanks. This lower carryover reduces the required replenishment rate for the processing solutions, leading to a cost saving.^[1]
Rapid washing and reduced water use: Unlike fiber-based papers, RC papers require minimal washing, leading to significant savings in water and processing time.
No need for ferrotyping: The surface gloss was inherent to the material, eliminating additional finishing steps. The surface texture of a RC print is produced during manufacture by a chill roller that cools the polyethylene immediately after coating. The use of a smooth chill roller produces a RC paper that has an inherently glossy surface, eliminating the need for ferrotyping. The use of textured chill rollers produces papers with similarly textured surfaces, such as luster and semi-gloss papers.
Quick drying: Even in thin coatings, polyethylene provides a significant barrier to water and water vapor, so in processing the paper support never absorbs chemical solutions or wash water beyond a small area of the uncoated edges. The effect being that at the conclusion of processing the gelatin emulsion is the only element of the photograph with a considerably elevated moisture content, allowing drying to proceed rapidly.

However, RC papers also introduced the extensive use of polyethylene in photographic materials, a synthetic polymer that is non-biodegradable and susceptible to chemical and physical degradation under adverse storage conditions.

RC supports were manufactured by extrusion coating polyethylene (PE) onto a paper stock that was specially prepared for the purpose and often already printed with the photographic manufacturer’s back print (e.g. name, logo). The emulsion-side PE layer is pigmented white, principally with titanium dioxide (TiO₂), to provide opacity and a bright white base, replacing the visual function of the baryta layer found in fiber-based prints. The PE coating on the back side of the paper support was kept clear, allowing the photographic manufacturer’s back print, if present, to be seen through the polyethylene. An extremely thin anti-static coating is applied to the outer surface of the back polyethylene layer. In addition to minimizing static electricity, this coating can be designed to facilitate writability with a pencil, ink reception, and to aid the interleaving of prints for agitation purposes when tray processing.

Titanium dioxide has very good covering power and whiteness when incorporated into polyethylene. However, the pigment, particularly in the anatase form, facilitates light-induced oxidation of polyethylene, leading to embrittlement and cracking.^[2]^[3]^[4] Various treatments, such as the incorporation of antioxidants have been used to address this problem.

Although the exact composition of RC supports varies by manufacturer and time period, Kodak RC color prints after 1988 typically included the following layers and additives:^[5]

Emulsion layers: Cyan, magenta, and yellow dye-forming layers
Pigmented PE layer (emulsion side): Titanium dioxide, zinc oxide, optical brightening agents (OBA), magenta dye
Raw base: Paper fiber, titanium dioxide, OBA, antioxidants
Clear PE layer (back side)
Anti-static layer: Typically composed of colloidal silica

History and Chronological Development[edit | edit source]

1920s: Positype water-resistant gelatin silver papers. Water-resistant material: Cellulose nitrate. Designed for aerial mapping, photo booths, and other applications requiring improved dimensional stability or quick processing times.
1940s: Kodak water-resistant gelatin silver papers. Water-resistant material: Cellulose acetate. Designed for aerial mapping, photo booths, and other applications requiring improved dimensional stability or quick processing times.
Mid 1960s: Kodak Kind 1594 paper.^[6] Water-resistant material: Polyethylene (PE). Early gelatin silver RC paper sold for specialized applications, such as aerial mapping and photogrammetry, that required high dimensional stability.
Mid 1960s: Kodak Resisto paper. Water-resistant material: Polyethylene (PE). Early branded gelatin silver RC paper with emphasis on durability and faster drying times. Kodak’s Resisto started out as a cellulose acetate coated water-resistant paper, but the tradename was maintained after transitioning to a polyethylene coated RC support in the 1960s.
1968: Kodak Ektacolor RC paper.^[7] Water-resistant material: Polyethylene (PE). The first commercially available RC color paper.
Mid 1970s: Agfa-Gevaert, Fuji, G.A.F., Ilford, and 3M start manufacturing RC papers. Water-resistant material: Polyethylene (PE). RC paper production becomes industry standard across major manufacturers.
1979: Ilford Cibachrome RC Paper.^[8] Water-resistant material: Polyethylene (PE). Silver dye bleach color paper for printing from transparencies (slides); later known as Ilfochrome.

Late 20th century: Dye sublimation and inkjet RC papers. Water-resistant material: Polyethylene (PE). RC papers with microporous or swellable receiving layers. Developed for digital photo printing, combining traditional photo feel with non-silver digital compatibility. RC paper also preventing cockling from the application of water based printing dyes.^[9]

Deterioration Concerns and Manifestations[edit | edit source]

It is important to distinguish RC papers from the earlier “water-resistant” supports that were used in the first half of the 20^th century. These predecessors to RC are typically baryta papers coated on both sides with a cellulose ester plastic prior to emulsion coating. The papers were almost exclusively used for niche applications where rapid processing and/or increased dimensional stability were desired, such as photobooths and aerial photography. RC papers with PE coating are in theory more chemically stable, though early water-resistant papers are frequently in good condition. Early water-resistant papers can be distinguished from PE coated RC paper using several techniques, including a known date of production, a back print (the early water-resistant paper will not have one), chemical or solubility spot tests (on the versos), and chemical analysis techniques (such as XRF (presence of barium vs. titanium) and FTIR).

Some conservation issues or deteriorations include:

Embrittlement or delamination of the PE layers: Polyethylene can become brittle or delaminate from the paper core, especially along fold lines or when exposed to fluctuating temperature and humidity.
Microcracking: Fine cracks may develop in the polyethylene due to the combined effects of oxidation induced embrittlement and the expansion and contraction of hydroscopic materials in the print from changes in relative humidity. In the most extreme cases this microcracking will give the surface of the print a craquelure appearance. The oxidation of the polyethylene involves a reaction of titanium dioxide with light and as such is confined to the white pigmented polyethylene layer directly beneath the emulsion. In the case of chromogenic color papers, the image will exhibit extreme fading by the time the polyethylene layer shows microcracking, due to the relatively poor lightfastness of the image forming dyes. Microcracking is principally a concern with early RC papers, as manufacturers made changes to reduce the risk of embrittlement.
Yellowing of the base layer or exhaustion of brightening agents: Optical brighteners and the paper core may change color over time due to light exposure or oxidative degradation, often appearing as general yellowing or uneven staining.
Edge penetration stains (trapped processing solution residues): The edges of RC papers are not sealed by the polyethylene coatings, allowing processing solutions to migrate approximately 1 mm into the paper. Due to the shortened wash times and limited access, these solutions remain in the edges of the paper, where they frequently create an orange-brown or gray stain, visible from the verso. Not all RC prints exhibit edge penetration stains. The paper’s sizing, the processing solutions, trimming, and the means of processing (type of mechanized processor, etc.) affect edge penetration.^[10]^[11]
Planar distortions: Localized distortions such as planar warping, dimpled surfaces, or edge lifting can occur due to internal stress between the emulsion and the paper core. The polyethylene coating the paper provides an effective, but not perfect moisture barrier, delaying the paper from reacting to extremes in the relative humidity of the storage environment, but not preventing them. The polyethylene can be seen as providing a buffer to moisture moving in and out of the paper core. The gelatin emulsion will react substantially faster to changes in relative humidity, which can lead to curling and other planar distortions.
Adhesion or blocking: When exposed to high humidity or water RC prints can adhere (block) to each other, glazings, or other housing materials in the same manner as fiber-based photographs with gelatin emulsions. The conservation treatments used on fiber-based materials often differ though due to the water-resistant nature of the RC supports, which precludes treatments that rely on introducing moisture from the verso.

Conservation Treatment[edit | edit source]

Mending: The adhesives that can be used to secure a mend to the verso of a RC print will depend on the back coating applied to that particular paper. Generally, the bond achieved with wheat starch paste is weak. Non-aqueous adhesives, such as Klucel G in ethanol, have been used effectively for mending and hinging. Testing should always be carried out to ensure sufficient strength and satisfactory reversibility. When evaluating the latter, the use of a specular light facilitates observing alterations to the back coating, which can be easily marred.

Flattening: The very low water permeability of polyethylene, even the extremely thin polyethylene coatings on RC paper, make traditional humidification techniques for flattening impractical, and run the risk of over softening the gelatin emulsion and beading water on the verso with little gained in the typical time frame. For this reason, heat in combination with pressure (e.g. flattening in a dry mount press) is generally the chosen technique for pronounced distortions. The temperature of the dry mount press is critical though, and the lowest effective temperature should be used to lessen the risk of largely irreversible surface texture alterations. Excessively high temperatures risk melting the polyethylene layers, with disastrous results. The density of the polyethylene used in the pigmented coating beneath the emulsion and the clear coating on the verso can be different and thus have different melting points. Polyethylene also melts over a range, so staying well below a referenced melting point in any conservation treatment of RC prints is advisable. Manufacturers of RC papers and dry mount tissues designed for mounting them, recommend not exceeding a variety of temperatures, though these are generally near or below 200F.

Minor planar distortions may not require heat at all. Prolonged weighting, such as in a blotter stack, can effectively remove many low distortions.

Emergency Response[edit | edit source]

Stacks of RC prints that get wet or are exposed to high humidity environments will eventually adhere together strongly (block), but the complete drying of a stack can be a very slow process due to moisture absorbed into the emulsions becoming trapped between polyethylene layers. As a result, a stack of recently blocked RC may appear outwardly dry, while the gelatin emulsion in the blocked areas still retains a high moisture content. In some cases, the moisture content may be high enough even several days after a disaster that these prints can be carefully separated without introducing additional water. This property of retaining moisture does however increase the risk of mold damage when blocked prints cannot be separated or dried out in a timely manner, particularly if the prints were saturated with untreated water, such as flood water from a natural disaster. In the worst-case scenarios, the gelatin emulsions will lose all structural integrity. These prints can be separated dry with little effort, revealing a diffuse vestige of an image on the original print support and the previously blocked surface.

In some situations, RC prints may only weakly block together over small areas. In these instances, the prints can sometimes be separated using mechanical action alone. Employing a peeling motion with a rigid tube or rod of 2 to 3” diameter against the print being removed will help to control the angle of separation and reduce the risk of inflicting creases accidentally. For this technique it is critical that the blocked area(s) are small enough to still allow the prints to flex. Extreme care and close examination must be observed, as forcing apart strongly blocked prints dry can result in major damage. When RC prints are blocked together strongly an immersion treatment is generally required. Reducing the temperature of a bath can lessen the risk of over softening the gelatin emulsions of blocked prints in an immersion treatment. These treatments are high risk and should only be carried out by a trained photograph conservator.

Preservation Recommendations[edit | edit source]

References[edit | edit source]

Eastman Kodak Company. Using Kodak Ektacolor Chemicals. Eastman Kodak Co., 2011.
Renfrew, A., and Phillip Morgan, editors. Polythene; the Technology and Uses of Ethylene Polymers. [2nd ed.], Iliffe; Interscience Publishers, 1960.
Parsons, T. F., G.G. Gray, and I.H. Crawford. “To RC or Not to RC.” Journal of Applied Photographic Engineering. 5 (2): 110–117. 1979.
Wagner, Sarah. “An Update on the Stability of B+W Resin Coated Papers.” Topics in Photographic Preservation, vol. 8, 1999, article 9, pp.60-66.
Weaver, Gawain, and Zach Long. “Chromogenic Characterization: A Study of Kodak Color Prints, 1942–2008.” Topics in Photographic Preservation, vol. 13, 2009, article 13, pp. 67–82. Presented at the 2009 PMG Winter Meeting, Tucson, Arizona.
Wilhelm, Henry Gilmer, and Carol Brower. The Permanence and Care of Color Photographs: Traditional and Digital Color Prints, Color Negatives, Slides, and Motion Pictures. First edition, Preservation Publishing Company, 1993.
Moore, Peter. “The New World of Resin Coated Papers.” PMI Photo Methods for Industry. vol. 17, no.3. Gellert Publishing Corp., March, 1974.
Pénichon, Sylvie. Twentieth-Century Color Photographs: Identification and Care. Getty Conservation Institute, 2013.
Bugner, Douglas. “Papers and Films for Ink Jet Printing.” Handbook of Imaging Materials. 2nd ed., rev. and expanded, edited by Arthur S. Diamond and David S. Weiss. Marcel Dekker, 2002, pp. 603-627.
"Resin coated photographic base manufacture," report, 1980, Box: 83b, Folder: 11. Kodak Historical Collection, D.319. Rare Books, Special Collections, and Preservation, River Campus Libraries, University of Rochester.
Funderburk, Kit, and Eastman Kodak Company. History of the Papermills at Kodak Park. [Eastman Kodak Co.], 2006.