To kick off a new year of blogging, I thought it would be interesting to discuss a few forms of photographic material degradation, their causes, and steps one can take to prevent them. One form of degradation that affects silver based photographic materials is silver mirroring, which manifests physically as a reflective, bluish cast that appears in the deepest shadows of a print or negative when it is examined in raking light. Silver mirroring is often a good indication that older photographic materials have been subject to improper storage and unchecked humidity. According to Bertrand Lavadrine, silver mirroring is a two stage process. “First, air pollution and moisture oxidize some of the silver that forms the image. The silver ions migrate to the surface of the gelatin. When the ions come into contact with the atmosphere, they are transformed into metallic silver (colloidal silver) and silver sulfide.” It is also important to note that the location of silver mirroring on a print or negative is indicative of specific archival storage issues. For instance, as Gawain Weaver observes in A Guide to Fiber-Base Gelatin Silver Print Condition and Deterioration, silver mirroring that appears around the edges of a print or negative is most likely the work of humidity and air pollutants while silver mirroring that appears throughout or in localized areas of a print or negative is most likely caused by contact with wood pulp based papers, mats, or storage containers. A simple way to prevent or mitigate the threat of silver mirroring is to store photographic materials in a cool, dry place. Also, always store photographic materials in containers that pass the Photographic Activity Test. Check out the George Eastman House‘s website for more information about silver mirroring and other forms of photographic degradation. More posts about other forms of degradation to follow.
–Information gathered from: Lavedrine, Bertrand. A Guide to the Preventative Conservation of Photographic Collections. Los Angeles: Getty Publications, 2003. Print. and Gawain Weaver, A Guide to Fiber-Base Gelantine Silver Print Condition and Deterioration, electronic publication, April 2008. Photographs: USD Photograph Collection, Series 4.