Gelatin Dry-plate Negative

Page Information
Date initiated	January 2021
Contributors	Elsa Thyss (Page Compiler) , Emma Cieslik

Gelatin Dry-plate Negative

Historical Facts

Invented: Maddox (1870), J. Johnston (1873), King (1873), C.E. Bennett (1874), R. Kennett (1874).
Patented: G. Eastman patented a coating machine to manufacture dry plates in 1880.
Historic Practitioners: Eugène Atget, Nadar, Lewis Hine, Karl Blossfeldt, E.J. Bellocq, Anne Brigman
Contemporary Practitioners: Mark Osterman, Nick Brandreth, Denise Ross, Jonathan Stead

The invention of the gelatin silver process in the UK

Since the 1850s, pioneer photographers experimented with various organic materials to be used as a binder to hold the silver on glass plate negatives. The British Richard Maddox was the first to publish a working method using gelatin in The British Journal of Photography in 1871. In this article, Maddox described how he mixed gelatin, water and silver halides, coated the resulting emulsion onto a clear glass plate, and left it to dry. After he exposed the sensitized plate to sunlight, he poured his development solution made of pyrogallic acid and silver nitrate onto the plate, washed it, and then fixed it with a regular solution of hyposulfite of soda. At the end of the paper, he concealed that many adjustments had to be refined. Indeed, the process proposed by Maddox was not immediately successful – it was actually less light sensitive than collodion plates – but it was a major starting point which would be followed by many improvements in the following years, leading to what would be a revolution in the history of photographic processes. The major improvements following Maddox’s publication in the 1870s:

• 1873: The washing of the emulsion to remove the potassium/ammonium nitrate (J. Johnson).
  
• 1874: The ripening of the emulsion with heat to increase sensitivity (C.E. Bennett).
  
• 1874: The addition of iodides and chlorides to the emulsion (King and R. Kennett). Kennett’s invention is an emulsion that could be left to dry in sheets and later diluted in water when one wanted to use it. This dry material was called by Kennett the “sensitive pellicle”.

These improvements led to a photographic negative made and sensitized in advance, which could be kept for months or years without losing its light sensitivity.

In 1878, the English Company Wratten and Wainwright started to produce gelatin dry plates in London. Quickly after that, in the United Stated the process began to be developed at an industrial scale.

The industrial development in the US

The American industrials quickly perceived the advantages of the British invention: the increased sensitivity and the less perishable photosensitivity, made this process perfect for industrial production. Between 1879 and 1885, 3 companies started to produce glass plate negatives: Keystone, Cramer and Eastman, which will later become the Eastman Kodak Company.
The genius of George Eastman was to conceive and develop early on a machinery for the coating of plates and to patent it in the US and in Europe. In the 1880s, the sector reaches its apogee, many companies produce gelatin glass plates and are completely independent from the beginning to the end of the production chain. Major technical issues as solved during that decade, such as the extension of the area of light sensitivity of the emulsion to green and yellow (orthochromatic plates, erythrosine dye, 1884, Eder).
The number of new companies that produce only dry plates increases enormously in the 1890s, while older companies like Eastman Kodak enlarge their conceptions of their enterprise by producing other photographic materials. The same decade, the problem of halation, which is a blurring effect caused when very bright lights were photographed against a dark background, was solved by adding an opaque layer between the glass and the emulsion or on the back side of the glass to prevent the light from reaching the glass during the exposure (non-halation plates), which became quickly adopted by all the major companies.

Improvements in the early 20th century

By the early 20th century, professional photographers would be accustomed to using dry plates. They could buy a stock of negatives in advance and shoot their images later. The development could be done at another later point, as the latent image remained recorded, even several days or weeks later, thanks to the specificities of the gelatin silver developed out emulsion.

• 1905: A very important improvement of the process in the early 20th century was the development of panchromatic plates, sensitive to all the colors of the spectrum.
  
• 1906: The Wratten & Wainwright Company acquired an international reputation when started to produce the first panchromatic plates, with the collaboration of C.E. Kennet Mees.

Identification Characteristics

Gelatin Dry-Plate cross view diagram

Image layer: The image material is made of silver, embedded in a gelatin binder.

Silver mirroring on a gelatin dry plate negative

Color: The image material has a neutral grey to black color.

A very common deterioration of dry plate negatives is silver mirroring, which manifests itself in the form of blueish metallic sheen starting from the edges, sometimes covering the totality of the surface, and visible under reflected light. Improperly washed processing chemical can also be present on the negative as yellow or brown stains, visible in transmitted light.

Some dry plate negative exhibit an intense yellow color throughout their surface or locally. This is characteristic of negatives which exhibited a lack of density or contrast, and were therefore chemically intensified during a post processing step with a mercuric iodide or mercuric chloride solution. Over time, the mercuric halide has usually reacted with the silver making up the image to form silver iodide or silver chloride which are yellow and light sensitive.

Support: The gelatin binder lays on a transparent glass plate support of a thickness of 0.8 to 3 mm. According to the literature, most glass plates are first coated with a sub-layer or substratum made of gelatin hardened with chrome alum, to help the binder adhere properly to the glass support.

Conservation

Before attempting any treatment, it is essential to note whether any original retouching media is present on the binder or the glass side since their integrity should be respected.

Surface soil and grime

• On the emulsion side: To remove dust and lose particles, an air blower and a soft microfiber tissue, gently rubbed on the surface, can be used. For accretions and surface soil, one can use a cotton swab with hydrocarbon solvents or a mixture of water and ethanol (increase the proportion of water if needed to increase the solubility of the soiling media). Testing solvents on the emulsion beforehand is an excellent way to ensure the surface will not be disturbed. Areas with silver mirroring are extremely susceptible to abrasion, and rubbing in these areas may move or remove some image material.
• On the glass side: If no retouching media is present, the glass surface and edges can be cleaned with a cotton ball and a mixture of water and ethanol, and then dried with a soft microfiber cloth. A flat razor blade pushed parallel to the glass surface is an efficient technique to remove a stuck accretion.

Lifting emulsion

Gelatin emulsion lifting on a dry plate

Gelatin emulsion flaking on a dry plate

Depending on the typology and the extent of the emulsion lifting from the glass, various treatment techniques may be used. Historically, conservators have either removed the emulsion from the glass and stored it independently, transferred it onto another support, or used different adhesives to adhere the gelatin back onto its original support, with more or less success in the long term. To treat flaking emulsions, diluted gelatin applied with an ultrasonic mister has given satisfying results. When the lifting area is small, one can use a solution of warm gelatin applied on the glass surface to apply the gelatin binder back onto the support. Large areas of lifting emulsions are challenging, as an aqueous adhesive will likely cause the emulsion to swell and distort. In these cases, a less invasive approach to stabilize the object might be more suitable. For example, a protective sheet of glass can be attached to the negative, as for cracked plates.

Broken plates

• Cracks: A non-invasive treatment consists in lining the negative with a transparent glass plate of the same size, with a thin spacer between the plates. The two plates can be attached with transparent acrylic adhesive tape. Labeling the object condition may also help prevent future mishandling and increasing the crack.
• Breaks: A custom sink mat made of suitable materials can be made to house the fragments together. If needed, to restore the image readability for example, the broken dry plates may also be mended with a suitable adhesive such as Paraloid B72 after local testing of the solvents with the gelatin emulsion.

Glass deterioration

Crystalline or slippery deposits may be visible on the non-image side of the glass. This can be a chemical deterioration of the glass – more frequent on 19th-century glasses – due to the manufacture and storage conditions of the object. Storing the plates in a ventilated, cool and stable environment will help slow down this irreversible degradation process.

References

Historic Sources

• Clerc, L.P. (Louis Philippe). La photographie pratique : exposé complet de tout ce qu’il faut savoir pour obtenir de bonnes photographies. Paris : Charles Mendel, 1902.
• Cook, David J. More Light in Negative-Making. Rev. ed. St. Louis: H. A. Hyatt, 1905.
• Kennett, R. “On the Gelatino-Bromide Process, with a Description of an Easy Method of Working It by Using the `sensitive Pellicle’.” The Photographic News 18, no. 592 (June 19, 1874): 290–92.
• Maddox, Richard L. “An Experiment with Gelatino-Bromide.” The British Journal of Photography 18, no. 592 (September 8, 1871): 422–23.

Process and Historic Material

• Charriou, André. “Emploi des verres étirés dans la fabrication des plaques photographiques.” Sciences et Industries Photographiques 2, no. 6 (Juin 1930): 238–39.
• Lavédrine, Bertrand. “Gelatin Silver Negatives on Glass (1878-1940).” In Photographs of the Past: Process and Preservation, 244–51. Los Angeles: Getty Conservation Institute, 2009.
• Lavédrine, Bertrand, and Chantal Garnier. “Analysis and Restoration of Negatives Intensified with Mercuric Iodide.” Topics in Photographic Preservation 3 (1989): 12–21.

Further Reading

Historic sources

• Ackerman, Carl W. George Eastman: Founder of Kodak and the Photography Business. Beard Books, 1930.
• Anderson, J.A. “Indexing Negatives.” The American Annual of Photography, 1906, 94–98.
• Anonymous. Anthony’s Photographic Bulletin. The Anthony and Scovill Company, 1902. https://babel.hathitrust.org/cgi/pt?id=mdp.39015067043789.
• Baker, T. Thorne. Photographic Emulsion Technique. 2nd edition. American Photographic Pub. Co, 1941.
• Bennett, Charles. “A Sensitive Gelatin Emulsion Process.” British Journal of Photography 25, no. 934 (March 29, 1878): 146–47.
• Bennett, Charles. “Negatives with Gelatin Emulsion.” The Photographic News 22, no. 1052 (November 1, 1878): 524.
• Burton, W. K. The Development of Gelatine Dry Plates: A Practical Manual for the Amateur. Brunswick, Me: W.H. Burbank, 1890.
• Burton, W. K. Burton’s Modern Photography: Comprising Practical Instructions in Working Gelatine Dry Plates, Printing, Etc. 11th ed., rev. Enl. London: Carter & Co, 1894.
• Burton, W. K. “Preparing Glass: Coating It - Drying It and Packing Plates (Chapter XVIII).” In Burton’s Modern Photography Comprising Practical Instructions in Working Gelatine Dry Plates, Printing, Etc., 5th ed., 115–16. London: Piper & Carter, 1885.
• Burton, W. K., and G. Huberson. A B C de la photographie moderne: contenant des instructions pratiques sur le procédé sec a la gélatine. 3ème éd. Nineteenth Century Collections Online (NCCO): Photography:The World through the Lens. Paris: Gauthier-Villars, 1889.
• Clerc, Louis Philippe. Photography, Theory and Practice. London: George Brown, F.I.C., F.R.P.S., 1930.
• Cramer, G. Hints on Negative-Making. St. Louis: G. Cramer Dry Plate Co, 1902.
• Eder, Josef Maria. Modern Plates; or, Emulsion Photography. New York, NY: E. & H. T. Anthony & Co., 1881.
• Eder, Josef Maria. Theorie et pratique du procede au gelatino-bromure d’argent. Paris: Gauthier-Villars, 1883.
• Harrison, W. Jerome, W. I. Lincoln Adams, and Maddox. A History of Photography Written as a Practical Guide and an Introduction to Its Latest Developments. Scovill’s Photographic Series, no. 23. New York: Scovill Manufacturing Co, 1887.
• Johnston, J. “Hints to Gelatino-Bromide Workers.” British Journal of Photography 20, no. 706 (November 14, 1873): 544.
• “Retouching Negatives on the Glass Side.” Bulletin of Photography 17, no. 424 (September 22, 1915): 434–35.
• Sprange, Walter. “Primary Rules for Beginners.” The American Annual of Photography, 1903, 107–10.
• Whiting, Arthur. “Handwork on Negatives.” The Photo-Miniature: A Magazine of Photographic Information 10, no. 116 (June 1911): 353–87.
  

Process and Historic Material

• Brayer, Elizabeth. George Eastman: A Biography. University of Rochester Press. 1 vols. Rochester, N.Y., 1996.
• Brynjolf Pedersen, Karen, Ulla Bogvad Kejser, Mads Chr. Christensen, and Jesper Stub Johnsen. “Coatings on Black-and-White Glass Plates and Early Film.” In Coatings on Photographs : Materials, Techniques, and Conservation, edited by Constance McCabe, The Photographic Materials Group; 1St Edition edition. Washington, D.C: AIC, 2005.
• Barthe, Christine. “Gélatino-Bromure d’Argent sur Verre (Négatif au).” In Le Vocabulaire Technique de la Photographie, Marveal / Paris-Musees., 70–71. Paris, 2008.
• Deryagin, B. V., and S. M. Levi. Film Coating Theory. Focal Press, 1964.
• Gernsheim, Helmut, and Alison Gernsheim. “The Evolution of Dry Plates.” In The History of Photography. McGraw-Hill Book Company, 1969.
• Image Permanence Institute. “Gelatin Dry Plate.” Graphics Atlas. http://graphicsatlas.org/identification/?process_id=303.
• Kingslake, Rudolf. The Photographic Manufacturing Companies of Rochester, New York. 1st ed. Rochester, N.Y.: George Eastman House, 1997.
• Lavédrine, Bertrand, and Jean-Michel Susbielles. “Étude des Vernis des Négatifs sur Plaques de Verre.” Support/Tracé, no. 2 (2002): 25–32.
• Lavédrine, Bertrand. “Identification of Negatives.” In Photographs of the Past: Process and Preservation, 264–67. Los Angeles: Getty Conservation Institute, 2009.
• Neblette, Carroll B. Handbook of Photography and Reprography: Materials, Processes and Systems. Edited by John M. Sturge. 7th edition. New York: Van Nostrand Reinhold Company, 1977.
• Newhall, Beaumont. Latent Image: The Discovery of Photography. Doubleday, 1967.
• Salgado Aguayo, Cecilia, and Patricia Gonzales. “El uso de intensificadores en los negativos de Elias del Aguila.” In Redescubriendo a Elías del Águila: retrato fotográfico y clase media en Lima después de 1900, Instituto Cultural Peruano Norteamericano., 77–80. Lima, 2017.
• Sixou, Christian. Une Histoire de Plaques, L’industrie de la Plaque Photographique de 1850 à 1970. 1 vols. Paris: Christian Sixou, 2003.
• Valverde, Fernanda. Photographic Negatives, Nature and Evolution Processes. Rochester, NY: George Eastman House International Museum of Photography and Film, 2005. https://drive.google.com/file/d/1fg2jrp-C_VB37FQGkJF8MV3F8P8O9woh/view
• Wentzel, Fritz. “Early Gelatin Dry Plates in Europe and America.” In Memoirs of a Photochemist, 17–25. Philadelphia: American Museum of Photography, 1960.
  

Conservation

General on Dry Plates Conservation

• Allen, Sarah, and David Dungworth. “Conservation of the Bedford Lemere Photograph Collection at the NMR.” Research News 16 (2011): 36–38.
• Berselli, Silvia, Anne Cartier-Bresson, Karin Einaudi, Michael Hager, and Grant Romer. La Fragilità Minacciata; Aspetti e problemi della conservazione dei negativi fotografici. Roma: Unione internazionale degli instituti dei archeologia, storia e storia dell’arte in Roma, 1991.* Borýsková, Štěpánka. “Glass Plate Negatives – Conservation and Restoration in Practice,” 126. Prague: Institute of Chemical Technology, Prague, 2014.
• Cartier-Bresson, Anne. “Les négatifs: Méthodologie des traitements individuels.” In La Fragilità Minacciata; Aspetti e problemi della conservazione dei negativi fotografici, 23–32. Roma: Unione internazionale degli instituti dei archeologia, storia e storia dell’arte in Roma, 1991.
• Garnier, Chantal, and Francoise Flieder. “Les négatifs sur plaque de verre: conservation et restauration.” Les documents graphiques et photographiques : analyses et conservation. Travaux du CRCDG, 1984-1985, Archives Nationales, 1986, 207–42.
• Gillet, Martine. “Les Clichés Au Gélatino-Bromure d’argent Sur Plaque de Verre.” In Conservation et Restauration Du Patrimoine Photographique, Direction des Affaires Culturelles de la Ville de Paris., 66–69. Paris: Paris Audiovisuel, 1985.
• Gillet, Martine, Chantal Garnier, and Francoise Flieder. “Glass Plate Negatives; Preservation and Restoration.” Restorator 7, no. 2 (January 1986): 49–80.
• Grøntoft, Terje. “Air Quality Measurements for Preservation of Photographs,” 126. Prague: Institute of Chemical Technology, Prague, 2014.
• Herrera Garrido, Rosina. “Alfred Stieglitz’s Lantern Slides: History, Technique and Technical Analysis.” Andrew W. Mellon Fellow, fourth cycle Advanced Residency Program in Photograph Conservation, George Eastman House International Museum of Photography and Film, 2007.
• Herrera Garrido, Rosina. “Treatment of Alfred Stieglitz’s Lantern Slides.” Topics in Photographic Preservation 13 (2009): 170–80.
• Herrera Garrido, Rosina. “Emerge: La conservación de vidrio en fotografía. Casos prácticos: negativos en placa, autocromos y placas de linterna,” Jornadas de Investigacion Emergente en Conservacion y Restauracion del Patrimonio, 363–72, 2014.
• Koch, Mogens S. “Preservation & Treatment of Wet Plate & Other Negatives.” Presented at the Nineteenth Century Photographic Negative Processes Meeting, George Eastman House, Rochester, NY, June 2005.
• Lavédrine, Bertrand, and Chantal Garnier. “Analysis and Restoration of Negatives Intensified with Mercuric Iodide.” Topics in Photographic Preservation 3 (1989): 12–21. http://resources.culturalheritage.org/pmgtopics/1989-volume-three/03_03_Lavedrine.pdf
• Orraca, Jose. “The Preservation and Restoration of Glass Plate Negatives.” Image 16, no. 2 (June 1973): 8–9.
• Ostroff, Eugene. “Photographic Preservation, Modern Techniques,” 1974.
• Pietsch, Katrin. “www.Photographicnegatives.Net.” Topics in Photographic Preservation 12 (2007): 64–66. http://resources.culturalheritage.org/pmgtopics/2007-volume-twelve/12_12_Pietsch.pdf
• Puglia, Steven T. “Negative Duplication: Evaluating the Reproduction and Preservation Needs of Collections.” Topics in Photographic Preservation 3 (1989): 123–34.
• Salgado Aguayo, Cecilia. “Conservacion del fondo Elias del Aguila.” In Redescubriendo a Elías del Águila: retrato fotográfico y clase media en Lima después de 1900, Instituto Cultural Peruano Norteamericano., 69–76. Lima, 2017.
• Simcoe, Robert J., Edward Los, and Josh Grindley. “Harvard Plate Cleaning Machine,” 126. Prague: Institute of Chemical Technology, Prague, 2014.
• Weinstein, Robert, and Larry Booth. Collection, Use, and Care of Historical Photographs. Nashville American Association for State and Local History, 1977. https://trove.nla.gov.au/work/10975367?q&sort=holdings+desc&_=1558557628935&versionId=50580955.
• Whitman, Katharine. “Saving Images on Glass.” George Eastman Museum. Around the Museum (blog), 2007. http://www.dantrommater.com/conservation/graphics/articles/katy-close-up.pdf
• Whitman, Katharine. “The History and Conservation of Glass Supported Photographs.” Andrew W. Mellon Fellow, fourth cycle, George Eastman House, 2007.
• Whitman, Katharine. “The History and Conservation of Glass Supported Photographs.” George Eastman House, 2007.

Consolidation of Lifting Emulsion

• Albright, Gary E. “A Tentative Method for Consolidating Gelatin Dry Plates.” Topics in Photographic Preservation 7 (1997): 36–37. http://resources.conservation-us.org/pmgtopics/1997-volume-seven/07_05_Albright.pdf
• Derby, Deborah. “Singing The Blues: The Treatment of Water-Damaged Negatives.” Topics in Photographic Preservation 5 (1993): 84–88. http://resources.culturalheritage.org/pmgtopics/1993-volume-five/05_09_Derby.pdf
• Maheux, Anne F., and Wanda McWilliams. “The Use of the Ultrasonic Mister for the Consolidation of a Flaking Gouache Painting on Paper.” The Book and Paper Group Annual 14 (1995). https://cool.culturalheritage.org/coolaic/sg/bpg/annual/v14/bpga14-03.pdf
• Rempel, Siegfried. “Cleaning and Stabilizing Photographs.” In The Care of Photographs, Siegfied Rempel., 78–104. New York, NY: Lyons & Burford, 1987.
• Viars, Dominique. “Analyse et conservation-restauration des négatifs au gélatino-bromure d’argent vernis sur plaque de verre présentant un soulèvement de l’image.” Support/Tracé, no. 2 (2002): 33–39.
• Viars, Dominique. “Etude de douze plaques de verre négatives au gelatino-bromure d’argent vernies présentant des soulèvements d’émulsion, réalisées par l’atelier Nadar dans les années 1880-1886.” Masters Thesis, Institut national du patrimoine, 2001.
• Wagner, Sarah S. “A Preliminary Study: Consolidation of Gelatin Glass Plate Negatives with Organosilanes.” Topics in Photographic Preservation 3 (1989): 69–85. http://resources.culturalheritage.org/pmgtopics/1989-volume-three/03_11_Wagner.pdf
• Weidner, Marilyn Kemp. “Treatment of Water Sensitive and Friable Media Using Suction and Ultrasonic Mist.” The Book and Paper Group Annual 12 (1993). https://cool.culturalheritage.org/coolaic/sg/bpg/annual/v12/bpga12-16.pdf

Mending of Broken Plates

• Crow, Kelly. “Abe Lincoln’s Comeback.” The Wall Street Journal 249, no. 39 (February 16, 2007).
• Jamieson, Stephanie. “Repairing a Glass Lantern Slide: Stephanie Jamieson Sets out Some Tips for the Repair of a Glass Lantern Slide Using Vivak PETG.” Icon News, April 15, 2018, 34–36.
• Whitman, Katharine. “Conservation of an American Icon: The Reconstruction of the Lincoln Interpositive.” Topics in Photographic Preservation 15 (2013).
• Whitman, Katharine, and Ralph Wiegandt. “Case Study: Repair of a Broken Glass Plate Negative.” Topics in Photographic Preservation 12 (2007): 175–81. http://resources.culturalheritage.org/pmgtopics/2007-volume-twelve/12_25_whitman.pdf

Preventive Conservation

• Library of Congress, Washington, D.C. 20540 USA. “Negatives.” Web page. Accessed December 21, 2020. https://www.loc.gov/collections/genthe/articles-and-essays/deterioration-and-preservation-of-negatives-autochromes-and-lantern-slides/negatives/.
• McCabe, Constance. “Glass Plate Negatives: The Importance of Relative Humidity in Storage,” Sauvegarde et conservation des photographies, dessins, imprimés et manuscrits : Actes des journées internationales d'Etudes de l'ARSAG, 36–44. Paris: Association pour la Recherche Scientifique sur les Arts Graphiques, 1991.
• McCabe, Constance. “Preservation of 19th-Century Negatives in the National Archives.” Journal of the American Institute for Conservation 30, no. 1 (Spring 1991): 41–73. https://www.researchgate.net/publication/271690758_Preservation_of_19th-Century_Negatives_in_the_National_Archives
• Murata, Hanako, and Nora W. Kennedy. “Introduction to Glass Deterioration Issues in Photograph Conservation.” In Proceedings of XX International Congress on Glass. Kyoto, Japan, 2004.
• National Park Service. “Caring for Photographs: Special Formats.” Conserv’O Gram 14, no. 5 (June 1997). https://www.nps.gov/museum/publications/conserveogram/14-05.pdf
• Romer, Grant. “Problems and issues of photographic negative collection preservation.” In La Fragilità Minacciata; Aspetti e problemi della conservazione dei negativi fotografici, 11–22. Roma: Unione internazionale degli instituti dei archeologia, storia e storia dell’arte in Roma, 1991.
• The State Archives and Records Authority of New South Wales. “Conservation Tip 04: Rehousing Glass Plate Negatives,” n.d. https://www.records.nsw.gov.au/archives/collections-and-research/guides-and-indexes/conservation-tip-04-rehousing-glass-negs.
• Wagner, Sarah S. “Approaches to Moving Glass Plate Negatives.” Topics in Photographic Preservation 6 (1995): 130–33. http://resources.culturalheritage.org/pmgtopics/1995-volume-six/06_13_Wagner.pdf
• Wagner, Sarah S. “How Do I House Glass Plate Negatives?” National Archives, August 15, 2016. https://www.archives.gov/preservation/storage/glass-plate-negatives.html
• Wagner, Sarah S. “How Do I Move Glass Plate Negatives?” National Archives, August 15, 2016. https://www.archives.gov/preservation/holdings-maintenance/moving-glass-plate.html.
• Whitman, Katharine. “Housing Glass Transparencies.” Topics in Photographic Preservation 12 (2007): 182–85. http://resources.conservation-us.org/pmgtopics/2007-volume-twelve/12_26_whitman.pdf
• Whitman, Katharine. “Housing Glass Transparencies.” Topics in Photographic Preservation 12 (2007): 182–85. http://resources.culturalheritage.org/pmgtopics/2007-volume-twelve/12_26_whitman.pdf

Contemporary Practice

• Mark Osterman. http://thelightfarm.com/Map/DryPlate/Osterman/DryPlatePart4.htm; http://www.tiltgallery.com/mark-osterman/;
• Ross, Denise. “Gelatin Dry Plate Photography.” The Light Farm (blog). Accessed December 21, 2020. http://www.thelightfarm.com/Map/Books/cim/MapTopic.htm.
• Jonathan Stead. http://www.jonathanstead.com/index.html

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