Preservation Workshops : Identification and Deterioration of Photographic Prints
On March 23, 1999, the Harvard University Library Preservation Center and the Harvard College Library Preservation Services Department sponsored the first in a planned series of seminars that will address the nature and care of photograph collections. The opening seminar focused on the identification of 19th- and 20th-century photographic prints.
Julie Mellby, Assistant Curator in the Houghton Library Department of Printing and Graphic Arts; and Ann Whiteside, Visual Resources Librarian in the Frances Loeb Library, Harvard School of Design, worked with conference planner Lisa Biblo, HUL, Preservation Information Librarian, to identify topics of interest to the Harvard community.
Debra Hess Norris.
More than 75 curators, librarians, photographers, and preservation and conservation staff Debra Hess Norrisfrom the University's libraries and museums came to hear Debra Hess Norris, Director of the Winterthur/University of Delaware Program in Art Conservation and a leading expert in the preservation of photographs.
Photographic Print Processes
During the daylong seminar, Ms. Hess Norris discussed the major photographic print processes, including salt, albumen, collodion-chloride, silver-gelatin, platinum, cyanotype, and various color processes. Photographic prints, she explained, are made up of multiple components-usually the support layer (paper, for example, or plastic film); a binder layer (such as albumen, collodion, or gelatin), which binds the image to the support; and various materials that form the image itself (silver or pigment, for example).
Noting that the structural components of photographs determine their visual characteristics, Ms. Hess Norris outlined a system for identification, and in so doing, suggested a new way of "seeing" photographic images. For example, the color and surface texture of albumen prints, the products of a popular 19th-century technique, have much to do with the albumen binder layer (made of egg whites) that coats a thin paper support and imparts a glossy appearance. Gold-toned albumen images in good condition exhibit a warm purplish-brown tone. The silver image layer is formed from round silver particles that disperse light (rather than absorb it) and impart luminosity. The characteristics exhibited by photographs when they deteriorate also provide clues to their identification. The egg white binder in albumen prints, for example, is inherently unstable and often cracks and yellows. Also characteristic, when the silver image material is exposed to humidity it is altered and no longer reacts with light in the same way. The result is fading, loss of highlights, and a color shift from purplish brown to yellow brown.
Systematic Approach to Identification
Ms. Hess Norris described a systematic approach to identifying photographic prints. First, she says, observe the physical attributes of the print (texture, color, signs of deterioration). Note the date of the image (inscriptions and costumes can be helpful pointers) and relate it to the introduction of various processes. From this preliminary visual examination make an educated guess regarding print type. Next, use a microscope to examine the image and confirm the presence of identifying physical characteristics. Seminar participants experimented with this identification scheme, working in small groups with hand-held 30x microscopes.
The identification of photographs is not straightforward. A number of photographic processes share similar characteristics and are difficult to distinguish from one another. Prints from a single process can look very different, and there are occasional exceptions to the rules. Identification requires a trained eye and comes only with practice. The Preservation Center has begun to develop a study collection of print type examples that are available for examination.
Through her engaging and clear presentation, Ms. Hess Norris provided seminar participants with some fundamental tools for assessing the physical nature of photograph collections. Correct identification ultimately ensures more effective preservation.
Future Workshops
Future initiatives at Harvard will include seminars on identification of photographic negatives, as well as preservation management of photograph collections (including disaster preparedness).