NATURAL AGING OF PHOTOGRAPHS
STANTON ANDERSON, & ROBERT ELLISON
1 BACKGROUND AND PURPOSE
The stability of photographic images is of interest to manufacturers as well as private and commercial users of photographic films and papers. The most important image stability information comes from natural aging that most closely simulates actual use and storage. Information on light stability is useful, but dark stability is generally more important. All photographs experience the effects of dark-keeping, but many important processed images see little light exposure during their lifetimes.
Most image-stability data on photographic products come from accelerated testing evaluating either light or dark stability. Early photographic standards, for example, have been based on rather severe conditions, such as 60�C/70% RH (ANSI 1984). Conditions of this type provide quick results on the relative dark stability of products. However, it is now generally recognized that such single accelerated tests at extreme temperatures and humidities have limited value since they do not always correlate to actual keeping during use. The advent of Arrhenius testing, in which a series of temperatures are used at a constant humidity to make extrapolations to room conditions, has provided us with a more powerful tool (Bard et al. 1980). This type of prediction is widely employed at Kodak for research and development as well as for defining the stability of new products entering the market place.