In contrast to photograph degradation that occurs as a result of improper storage, the two problems I will discuss today start in the dark room. The first, sulfiding, affects the half tones of black and white prints, turning them from various shades of gray to yellow and brown. In addition, sulfiding can spread throughout a print, softening contrast and fading fine details in lighter areas. The root cause of sulfiding is improper washing during photographic processing. When a photographer fails to wash a black and white print thoroughly enough to remove all remaining fixer solution, fixer salts stay on the print. According to Bertrand Lavedrine, “The fixer that is left behind decomposes in the presence of high relative humidity to form colored silver sulfide stains.” Lavedrine also notes that storing prints in dry environments may help mitigate this process. It is also important to note that because the symptoms of sulfiding are similar to those of other forms of photograph degradation, it is often difficult to identify. Lavedrine states that chemical tests such as the methylene blue test or the silver densitometric test can determine the amount of residual fixer on a print. If one does not want to go through chemical testing, a simpler way to tell whether or not a print is subject to sulfiding is to smell it. The lingering fixing solution can leave a strong odor that, in the olfactory spectrum, registers some where between vinegar and rotten eggs.
The end results of insufficient fixing during black and white photograph processing are easier to identify. The lighter shades of gray in an affected photograph are stained with yellow or rust colored spots. Stains can also appear on the back of a print. These symptoms are generally caused by one of two errors during photographic processing: the use of an exhausted fixing bath or too short of a time in the fixing bath. In the case of the former, Lavedrine states, “the use of an exhausted fixing bath leads to the formation of insoluble silver complexes. It is thus impossible, even with a thorough wash, to remove them from the image. As time goes by, the silver salts might decompose into sulphurous acid or silver sulphide. The lighter areas of the photograph will turn yellow with the formation of silver sulphide while the halftones will be affected by the sulphurous acid.” If the fixing bath is not exhausted, but the print does not spend enough time in it, silver remains on the print surface, reacts with light, and forms colored stains. Unlike the symptoms associated with the use of an exhausted fixing bath, these symptoms generally appear immediately upon light exposure, alerting the photographer that the affected print should be discarded. Thus, it is pretty unlikely to see this type of photograph degradation in archival collections.
All of the above forms of photograph degradation are irreversible. The progress of degradation can be slowed through the proper maintenance and environmental control, but ultimately degradation eventually renders images indecipherable. It is of the utmost importance that photographs subject to degradation are quarantined from other photographic materials. The chemical processes at work on degraded images can spread to other photographic materials if the two are kept in close proximity. At the USD Archives and Special Collections, we’ve made it a priority to identify compromised photographs and store them separately from the rest of the photograph collection. Thus we ensure the health and continued conservation not only of individual photographs, but of the collection as a whole.
–Information gathered from: Lavedrine, Bertrand. A Guide to the Preventative Conservation of Photographic Collections. Los Angeles: Getty Publications, 2003. Print; Lavedrine, Bertrand. “The Yellowing of Black and White Photographs during Exhibition.” Centre de recherche sur la conservation des collections. Muséum national d’histoire naturelle. Web. 17 Feb 2012: http://www.crcc.cnrs.fr/spip.php?article156&lang=en; Photographs: Series 3, USD Photograph Collection, and Clay County Schools, Richardson Collection