Archival preservation of photographic films—A perspective

Abstract

Only black-and-white silver-gelatin photographic films processed according to ANSI IT9.1-1988 or equivalent ISO standards, 1,2 coated on cellulose (organic) esters, such as cellulose triacetate, CTA, or poly(ethylene terephthalate), PET, supports are considered as archival recording materials. For optimum preservation, these archival films should be kept at 21°C and 15–40% RH. 3 Strict adherence to the storage conditions is required to prevent degradation, as photographic film is a laminate structure of dissimilar materials differing widely in their hydrolytic stabilities. Longevity of the recorded information for retrieval and duplication after long periods of ambient storage requires ultimate stability of these flexible supports. This paper reviews the practival performance versus predicted estimations of usable life for films on CTA and PET supports and gives an account of the degradation reactions of the supports under ambient conditions. Slow hydrolysis of both CTA and PET is the primary degradation pathway at ambient temperatures, which is independent of the mode by which they are manufactured. However, PET is far less susceptible to hydrolysis than CTA. These hydrolytic reactions will begin long before any physical property losses are noticeable. Chemical inertness of these supports over the entire archival life span cannot be achieved, as total elimination of moisture from photographic films is not practicable. However, storage of these photographic films at 21°C and low relative humidities provides the archival life expectancy for their intended usage.