s e s s e c o r SILVER GELATIN P c i h p a r g o t o h P f o s e r u t a n g i S l a c i t y l a n A f o Dusan C. Stulik | Art Kaplan s a l t A e h T © 2013 J. Paul Getty Trust. All rights reserved. The Getty Conservation Institute works internationally to advance conservation practice in the visual arts—broadly interpreted to include objects, collections, architecture, and sites. The GCI serves the conservation community through scientific research, education and training, model field projects, and the dissemination of the results of both its own work and the work of others in the field. In all its endeavors, the GCI focuses on the creation and delivery of knowledge that will benefit the professionals and organizations responsible for the conservation of the world’s cultural heritage. The Getty Conservation Institute 1200 Getty Center Drive, Suite 700 Los Angeles, CA 90049-1684 United States Telephone: 310 440-7325 Fax: 310 440-7702 Email: [email protected] www.getty.edu/conservation The Atlas of Analytical Signatures of Photographic Processes is intended for practicing photograph conservators and curators of collections who may need to identify more unusual photographs. The Atlas also aids individuals studying a photographer’s darkroom techniques or changes in these techniques brought on by new or different photographic technologies or by the outside influence of other photographers. For a complete list of photographic processes available as part of the Atlas and for more information on the Getty Conservation Institute’s research on the conservation of photographic materials, visit the GCI’s website at getty.edu/conservation. ISBN number: 978-1-937433-13-0 (online resource) Front cover: Henri Cartier-Bresson, Gare Saint Lazare, 1932. Printed 1979. Silver gelatin print. © Henri Cartier-Bresson/Magnum Photos. Every effort has been made to contact the copyright holders of the photographs and illustrations in this work to obtain permission to publish. Any omissions will be corrected in future editions if the publisher is contacted in writing. 2 The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust CONTENTS Historical Background 4 POP Silver Gelatin Process 4 Identification: POP Silver Gelatin Photographs 7 DOP Silver Gelatin Process 24 Identification: DOP Silver Gelatin Photographs 28 Important Variants of the DOP Silver Gelatin Process 47 Identification: RC B&W DOP Silver Gelatin Photographs 48 Interpretation Guide 63 3 The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust SILVER GELATIN English: silver gelatin French: gélatino d’argent (tirage au) German: Silbergelatineabzug HISTORICAL BACKGROUND No single figure can be credited with the invention of the silver gelatin photographic process, which gradually became the most important photographic printing process of the twentieth century. Several inventors, including Peter Mawdsley, Josef Marie Eder, Giuseppe Pizzighelli, and Sir William de Wiveleslie Abney, can be credited with the most important contributions to its development and research of several key types of silver halide gelatin emulsions. The development of the baryta layer, even when not directly related to silver gelatin photography, goes back to its introduction by José Martinez-Sanchez and Jean Laurent in 1866. A silver gelatin print by Henri Cartier-Bresson appears in figure 1. Figure 2 shows a historical timeline of the silver gelatin photographic process. Silver gelatin photographic papers were available both as POP (printing-out paper) and as DOP (developing-out paper). Even though the internal chemical structure of both types is very similar, the handling and processing of each was quite different, and it is best to describe them separately. POP SILVER GELATIN PROCESS A number of different recipes for preparing silver gelatin printing papers were published in the photographic literature during the last quarter of the nineteenth century. The availability of commercially made silver gelatin photographic papers from photographic supply houses and catalog orders was responsible for the relatively limited preparation of photographic material by individual photographers. These photographers were still heavily involved in researching, testing, and providing recommendations for paper processing to achieve the best results or special effects for different tasks. This is well reflected in the lively discussions, idea exchanges, photographic literature, and number of photographic patents filed during that time for improvements in silver gelatin photography. 4 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust Figure 1 Henri Cartier-Bresson, Gare Saint Lazare, 1932. Printed 1979. Silver gelatin print. © Henri Cartier-Bresson/ Magnum Photos. Process Description The POP silver gelatin process involves the following steps: 1. POP photographic paper is placed under a negative into a special copy frame. 2. The copy frame assembly is exposed to daylight or artificial light until the image is developed to the desired image intensity. Guides for approximate exposure times were usually available from paper manufacturers for different lighting conditions, but some tests were needed to find good exposure conditions for a given light and negative combination. POP requires some level of overprinting because the image intensity is decreased during processing. 3. The exposed POP is washed in a water bath to remove any excess of soluble silver salts. 4. The washed POP is toned using different types of gold and platinum toners or using first a gold, then a platinum toner. Some toning formulas found in early nineteenth-century photographic literature also recommend using palladium or iridium toning. However, even after analyzing thousands of POP silver gelatin photographs, we still have not identified any existing photograph toned in that manner. 5. The toned POP photograph is washed again to remove toning chemicals and fixed using the standard hypo (sodium thiosulfate) fixer. 6. The toned and fixed photograph is thoroughly washed in running water or in multiple water changes in a water tray. 7. The washed photograph is air dried or surface polished by squeegeeing the print on a clean, polished glass and letting it dry. The fully dried photograph usually separates from the glass surface on its own. 5 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust Platinum toning 1889 1890s Matte DOP paper used introduced Kodak introduces baryta coating c. 1900 Baryta-based paper introduced (Germany) Popularity of glossy papers increases 1884 R. L. Maddox introduces Color photography becomes main positive printing process silver gelatin emulsion Ongoing from 1920 Ongoing from c. 1960 Only a small number of companies still producing B&W 1871 photographic paper 2012 1850 1875 1900 1925 1950 1975 2000 2025 1874 1930s 1970s 2005 First commercial Kodak announces end of its B&W 1900s 1940 silver gelatin paper photographic paper production 1885 Resin-coated (RC) papers introduced Commercial coating Variable contrast (VC) paper introduced machines 1893 Gevaluxe paper introduced 1890 Uranium toning introduced Sepia toning used 1900–1990 L. Baekeland introduces Velox paper Golden era of silver gelatin printing Figure 2 Timeline of the silver gelatin photographic process. 8. Many dried POP photographs are then retouched and mounted on a more rigid paper or paper board support. 9. Some photographs are varnished or surface coated to modify their appearance or to protect them from physical and environmental damage. Figure 3 shows a schematic cross section of a typical silver gelatin print. Main Application of the POP Silver Gelatin Process The POP silver gelatin process answered the need for easy printing of photographs from both large-format and, at that time, new small-format cameras. Some processes called for standard sun exposure, but many so-called gaslight photographic papers could be exposed in-house using gas lights or special photographic gas burners. Kerosene lamps or early electrical lightbulbs could 6 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust Figure 3 Schematic cross section of a typical POP silver gelatin photograph. also be used. POP was sensitive enough so that this type of light exposure could be performed within several minutes, but it did not require the complete darkness of a darkroom as later, more sensitive photographic papers did. Some hybrid POP photographic papers called for exposure followed—after some level of image was formed photogenically—by chemical development. POP photographic papers were also used as image-proofing materials to assess the quality of produced negatives. Bibliography (by date) Bothamley, C. H., ed. 1891. Ilford Manual of Photography. London: Hazell, Watson & Viney. Clerc, L. P. 1930. Photography Theory and Practice. Bath: Pitman Press, 313–80. Gevaert Company. 1938. Gevaert Manual of Photography. Belgium: Gevaert Company. Neblette, C. B. 1942. Photography: Its Principles and Practice (4th ed.). New York: Van Nostrand, 230–48, 290–379, 592–615, 644–61. Eaton, G. 1957. Photographic Chemistry. New York: Morgan & Morgan. Baines, H. 1974. The Science of Photography. New York: Fountain Press. Haist, G. 1979. Modern Photographic Processing. Vols. 1 and 2. New York: Wiley. Bernard, B. 1980. Photodiscovery. New York: Abrams. Brill, T. B. 1980. Light: Its Interaction with Art and Antiquities. London: Plenum. [Various authors]. 2010. Photographic Processes: Photomontage, Daguerreotype, Calotype, Autochrome Lumiere, List of Photographic Processes, Black and White. Wikipedia series. Memphis, TN: General Books LLC, 111–16, 183–202. Silver Gelatin–Related Patents Joseph Swan, English Patent 2,968 (July 22, 1879), silver bromide printing paper IDENTIFICATION: POP SILVER GELATIN PHOTOGRAPHS Visual Signatures Visual Characteristics The silver image of POP photographs is developed photogenically during light exposure. Photogenically developed silver particles are much smaller than chemically developed silver particles. The color of the silver image of a POP silver chloride photograph relates to the size of the silver particles and usually ranges from light yellow-brown to red and darker brown (fig. 4). 7 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust F igure 4 Antique POP silver gelatin photographs in a range of colors. The color of silver bromide POP images is usually cooler and grayer. These visual clues hold only for POP photographs that have not been toned. Most silver gelatin POP photographs were gold toned. The toning process increases the size of silver particles; however, the growth of image particles is not straightforward (there is some deposition of gold onto the silver particles, but our analysis of POP photographs during toning and of the gold bath after toning shows a growing concentration of silver in the gold bath during toning). Toning usually shifts the image color to red-violet or dark black-violet. Some POP photographic papers were available with tinted (usually pink or blue) baryta layers (fig. 5). This is not a good visual clue because many albumen and silver collodion photographs produced during that time had a similar type of coloration. Silver gelatin POP was produced in several surface-texture qualities. At first only glossy or matte surfaces were available, but after the turn of the twentieth century the number of available textures increased. Later some specialized POP papers became available. Some POP papers tried to mimic the visual appearance of more expensive and very fashionable carbon or platinum photographs. POP photographs with unusual sheen or high gloss, unusual thicknesses, or a tendency to curl may indicate the presence of a surface varnish or coating (fig. 6). Microscopic Characteristics Even when toned, silver-gold image particles of POP silver gelatin photographs are too small to be visible even with a powerful optical microscope. When observed under a stereomicroscope at high magnification, the particles are not visible. A detailed inspection of the boundary between dark and light areas reveals a darker “cloud” of imaging material that looks almost three dimensional, “floating” above the underlying white surface of the baryta layer (fig. 7). 8 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust Figure 5 POP silver gelatin photographs with pink and blue baryta layers. Figure 6 POP photograph showing a tendency to curl, Figure 7 Detail of a POP photograph (80× magnifica- which may indicate the presence of a surface coating. tion), showing the presence of a dark “cloud” of imaging material above the white surface. 9 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust Figure 8a Detail of a POP photograph (40× magnifica- Figure 8b Detail of a POP photograph (40× magnifica- tion), showing the presence of the baryta layer at the tion), showing the presence of the baryta layer at a edge area. damaged corner area. With the exception of very early silver gelatin POP and some later types of technical and copy POP, almost all other POP papers were produced using a baryta-coated paper stock. The presence of a baryta coating and the characteristic three-layer structure of the paper can be observed when inspecting the edges of a photograph under a microscope. Even very well preserved photographs may have slightly damaged edges or corners that show fibers of the paper substrate and some separated microplatelets of the white (more white than the paper fibers) baryta layer still embedded in the paper fibers or held by the damaged emulsion layer (figs. 8a, 8b). When edges or corners of a photograph are not accessible for inspection, the presence of a baryta layer can often be detected within the very light areas of the photograph. Focusing on the surface layer of the image and slowly refocusing through the emulsion layer reveals an absence of paper fibers. Under high magnification, the baryta layer looks flat, solid, and almost structureless. Early silver gelatin photographs were not protected against mechanical damage by a top or supercoat of hardened gelatin. Thus, many handled POP photographs exhibit some surface scratches to the gelatin layer. These can be observed during inspection under a stereomicroscope. The gelatin layer is usually thicker than the thin collodion layer, which may have some scratches down to the white baryta layer. An uncoated gelatin layer also does not show the presence of a microcracking pattern, which is typical for older albumen photographs (fig. 9). Analytical Signatures XRF The typical XRF spectrum for the majority of POP silver gelatin photographs shows the presence of silver (Ag) and gold (Au). Both are imaging metals of toned POP silver gelatin photographs. The majority of photographs also show the presence of a baryta layer identified by the presence of barium (Ba) and strontium (Sr) in the XRF spectrum. Other elements detected—calcium (Ca) and iron (Fe)—may be present as impurities in both the paper base of the photographs and the 10 SILVER GELATIN The Atlas of Analytical Signatures of Photographic Processes The Getty Conservation Institute, © 2013 J. Paul Getty Trust