Abstract
Silver gelatine photographs were the most dominant photographic process of the twentieth century from the 1880s until the 1960s. They are prone to yellowing, mirroring and fading which is largely attributed to the effects of pollutants, relative humidity and residual processing chemicals. Experts in the conservation of photographs claim they can determine the causes of deterioration with the naked eye: the effects of humidity result in a more yellowed appearance, whilst the presence of residual chemicals results in a redder appearance. This work aims to investigate if the same deterioration processes can be diagnosed in photographic prints with a spectrophotometer by addressing two questions: (1) In new and artificially aged silver gelatine photographs is it possible to distinguish between discolouration caused by silver migration and that caused by the presence of residual sulfur? (2) What are the complexities of applying these findings to historic photographs? A set of test photographs, some well processed and some insufficiently washed was developed and artificially aged. These were compared to a small collection of historical photographs of different ages, paper types and image colours. Samples were assessed using visual observation, residual silver and hypo spot tests, colour measurements including L*a*b* and reflectance spectra, Fourier transform infra-red (FTIR) spectroscopy and transmission electron microscopy (TEM). After artificial ageing the well processed test photographs were more yellowed, TEM indicated that this was due to colloidal silver formation. The insufficiently washed test photographs were more red but also darker, TEM showed these samples to have more homogeneous silver filaments, thought to be due to silver sulfide formation. The results for the historical photographs were similar but more subtle. A larger sample set is needed to investigate this more extensively. Further investigation on historical samples, with colour measurements and residual silver and fixer spot tests will take place.
Highlights
Black and white silver gelatine photos were the most dominant photographic process of the twentieth century from their introduction in the 1880s until the 1960s when they were superseded by chromogenic photographs and digitally printed images
Test photographs before ageing The following results focus on one paper type, fibre based matt
They showed similar effects with greater reflectance in the red at 480– 740 nm in the insufficiently washed samples, see Fig. 4. These results indicate that a more yellow colour may correspond to the migration of image silver whilst a more reddish colour may correspond to the presence of residual fixer, providing a better understanding of the causes of damage, without resorting to destructive testing
Summary
Black and white silver gelatine photos were the most dominant photographic process of the twentieth century from their introduction in the 1880s until the 1960s when they were superseded by chromogenic photographs and digitally printed images. A developed out silver gelatine photograph is composed of an image forming layer, a binder and a support layer. A typical processed silver gelatine print on fibre-based paper has a light sensitive emulsion composed of silver particles suspended in gelatine, attached to a paper base coated with. Moon and Curran Herit Sci (2017) 5:45 a baryta layer: barium sulphate in gelatine. The light sensitive emulsion is attached to a paper base coated with polyethylene (PE). The PE on the image side contains a pigmented layer, usually titanium dioxide
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