Effects of Poliutant Vapors on Image Permanence

In the complex situation of a real archives or library, the contribution that air pollution makes to the fading of images is not easy to measure or observe. The effects are subtle and occur slowly, blending in with the action of light, heat, humidity, and the inherent stability (or instability) of each individual type of photograph. We are not able to say what percentage of the fading of a color print is due to air pollution. We know it causes some fading, but the thermal fading characteristics of color materials are probably the major factors. Because of the chemical nature of images (including in that term products commonly used in still photography, cinema, microforms, and color hard copy output from computers), it is a reasonable expectation that airborne pollutants would act to destroy them. Color images are usually comprised of organic dyes, which depend on complex structural arrangements within the dye molecule to absorb light. Disturb that precise structure at the right spot, and a yellow dye becomes colorless, or a cyan dye becomes a weak yellow. Black-and-white photographic images are comprised of metallic silver, which must first become oxidized before it can degrade; but, with silver, the response to atmospheric pollutants is complex and depends on more than just the presence of an oxidant. The subtle interactions of the component gases of air pollution are an intriguing problem and were a major focus of this research.