Lifetime of colour photographs in mixed archival collections

Abstract

Chromogenic prints, which make up around 99% of all colour photographs, are \namongst the most vulnerable materials in archival storage. However, although environmental \nstandards for storage are available, antagonistic requirements within \narchives mean that the recommended conditions are not always appropriate. This \nstudy evaluated the impact of mixed archival storage on chromogenic prints by following \nthree lines of research: environmental, material and values. \nDuring storage, three environmental parameters predominantly influence chromogenic \nprint lifetime: temperature, relative humidity (RH) and pollutants. The \npollutant of greatest interest was determined to be acetic acid as it is the most \nabundant pollutant within archival boxes and also causes greatest changes in dye \nconcentrations. \nMaterials research focussed on the development of two non-destructive analytical \nmethods. The first used the sRGB colour model for monitoring dye concentrations. \nThe second combined near infrared spectroscopy to develop applications for dating \nand stability prediction of chromogenic prints. \nThe third line of research related to values, specifically fitness-for-purpose of \nan image within the context of an archival collection. A psychophysical approach \nwas taken to determine the point at which colour changes are no longer acceptable, \ndefined as the unacceptability threshold. It was identified that while assessor \ncharacteristics did not affect the threshold, image characteristics, particularly fading \nprofile and image detail, did. \nHaving investigated the three lines of research separately, their integration led \nto a more holistic approach. Accelerated degradation experiments were planned \nusing design-of-experiment principles to develop a multiparametric dose-response \nfunction. The function relates the rate of degradation to temperature, RH and \nacetic acid concentration. This allowed for isoperms and isochrones, which connect points of equal permanence and lifetime respectively, to be developed. \nFinally, an innovative photographic lifetime calculator has been developed using \nprinciples of stock modelling and the developed damage function, thus incorporating \nmaterial and value change dependent upon environmental parameters.

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