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Photographic Materials Conservation Catalog
Date: Initiated March 2014
Contributors: Luisa Casella
The Photographic Materials Conservation Catalog is created and maintained by the Photographic Materials Group of the American Institute for Conservation for the convenience of the membership. The treatments, methods, or techniques described herein are provided for informational purposes. The reader assumes responsibility for any application results or interpretation of information.
Gelatin Dry-Plate Negative
Invented: Richard Leach Maddox developed the silver bromide emulsion in 1871. The process had to undergo several improvements before it could be an improvement to the use of collodion, eventually becoming faster and allowing for plates to be coated well before exposure time and developed later as well.
In 1873 John Burgess commercialized bottled gelatin silver bromide emulsion, stating it would allow anyone to coat their own plates. The product had problems such as crystalline soluble salts formed by the interaction of bromide and silver nitrate.
Commercial plates started being produced in 1875, coated on one side with gelatin containing a light sensitive silver halide. The plate was loaded onto a plate holder in the dark and exposed in camera. The photographer would develop, fix and wash the plate (possibly applying retouching or coatings after drying).
In 1877, Sir John Swan discovered that cooking the emulsion increased sensitivity and Charles Bennett introduced the ripening step to the process. As a result, dry plates exposures could be 1/20th of that of collodion plates.
Significant improvements were also made by adding dyes to the emulsions, expanding the spectrum of the light sensitivity from the initial UV/blue to yellow/green (orthochromatic plates, 1884) to full light visible spectrum (panchromatic, 1906), the latter development allowing for the introduction of [Autochrome| color photography].
Main Period of Use: 1880 - 1925
See Graphic Atlas for excellent identification and deterioration illustrations
Image layer: Filamentary (developed) silver, neutral gray in tone. May have retouching and varnish. If plate was intensified with mercuric iodide it may have a bright lemon-yellow appearance (silver-iodide).
Binder: Gelatin all the way to the edge of the support.
Support: Glass coated on one side with the emulsion. May have masks applied to opposite side of the image layer (red inks, paper masks). Glass plates came in a range of standard sizes established in 1891 after the International Congress of Photography in Brussels.
The plates were commercially available as a glass plate coated with a gelatin emulsion with a light-sensitive silver halide. The plate was loaded onto a plate holder in the dark and exposed in camera. A latent image was formed and the plate was then chemically developed. During development filamentary silver particles formed. The size and shape of these silver particles produce a neutral image tone. The plates were fixed and washed. Intensification baths could be used if the image was weak, such as mercuric iodide. Graphite retouching or coatings could be applied after drying. A variety of varnishes were used as coating, sometimes only on the face area of a portrait to allow for retouching on that area.
Conservation and Treatment
- High humidity may cause mold to appear on the emulsion and/ or plates to stick together
- Emulsion cracking or detaching along edges due to high temperatures or drastic variations in relative humidity and temperature; glass deterioration; or original manufacture problems
- Gelatin binder may present discoloration and/or stains with a variety of possible causes ( defective processing; inherent problems of residual chemistry; environmental pollutants; contact with poor quality materials; relative humidity and temperature variations)
- Breakage of the support is common due to mishandling or improper storage
- Glass deterioration (weeping glass, milky glass)
- Formation of silver mirroring
- Broken supports may be reattached; different adhesives have been successful (Whitman, 2003)
- Delaminating emulsions may be consolidated
Handling, Housing and Storage
- Plates should be housed in four flap paper envelopes that have passed the PAT.
- Storage boxes should not be to large in order to reduce their weight, and should be stored in mid to lower shelves.
- Plates should be handled with clean, dry hands (gloves will reduce the grip and may risk dropping the object), avoiding touching the image layer (fingertip grease will affect the binder and silver). When handling plates, work over a clean surface and do not lift the object to far from it.
- As with any artwork avoid speaking over the object to avoid risk of spitting to deposit over it.
- Do not leave object over light table for long periods of time. Insure light table does not get hot. If it does, work in small periods of time, turning the light off to cool down regularly.
- Commercial plates will likely have hardened gelatin binder. Water damage will still cause it to soften and the image layer should not be touched. Plates should be removed from enclosures, rinse in clean cold water is possible/ needed, and air dried with care not to be in contact with anything on the image side.
- Follow previous handling recommendations.
- GEH Lincoln Negative - https://www.youtube.com/watch?v=LEGcJGXjjT0
- Whitman, Katherine. 2003. "Conservation of an American Icon: the Abraham Lincoln Interpositive after Alexander Hesler, by George B. Ayres". Available at: http://www.notesonphotographs.org/index.php?title=Whitman,_Katharine._Case_study_1:_Conservation_of_an_American_Icon:_The_Abraham_Lincoln_interpositive_after_Alexander_Hesler,_by_George_B._Ayres
- Whitman, Katherine. 2003. "The History Conservation of Glass Supported and Protected Photographs". Capstone Research of the Advanced Residency Program in Photograph Conservation. George Eastman House, Rochester, NY. Available at: http://notesonphotographs.org/index.php?title=Whitman,_Katharine._%22The_History_and_Conservation_of_Glass_Supported_and_Protected_Photographs.%22
Process and Historic Material
- Encyclopedia of Nineteenth Century Photography, Available as a Google Book at: http://books.google.com/books?id=yVFdAgAAQBAJ&lpg=PP1&pg=PP1#v=onepage&q&f=false, page 438.
- Graphic Atlas: http://www.graphicsatlas.org/identification/?process_id=303
- Pedersen, Mark Scholer. "The silver gelatin dry plate process". Online article. Alternative Photography. Accessible at: http://www.alternativephotography.com/wp/processes/gelatin-silver/silver-gelatin-dry-plate-process