Fenech, A.; (2011) Lifetime of colour photographs in mixed archival collections. Doctoral thesis , UCL (University College London).

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Abstract

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

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