Bertrand Lavédrine, Director of the Centre de Recherche sur la Conservation des Collections (CRCC), CNRS, MNHN, MCC, Paris, France, outlines the latest research on the effect of lighting while preserving photographs.
Light exposure can damage photographs; gelatin silver prints are generally much more resistant to light-induced damage, although poor processing treatment may leave them vulnerable to light, and the optical brighteners incorporated in recent gelatin silver papers may be “extinguished” by large light doses.
Colour chromogenic process prints are considered quite light fugitive, even though since 1990 the light stability of some photographic papers has greatly improved. “Digital print” such as ink-jet prints were generally prone to rapid light fading in the first years of the new technology (late twentieth century), but the new generations of ink sets and substrates are believed to equal the light stability of current chromogenic process papers.
In consequence, the light fastness of an historical artifact is difficult to assess. The development of new tools such as the “microfading tester” could provide quantitative data on the light sensitivity of specific objects. Institutions that hold important photograph collections have adopted some rules for the exhibition of photographs that may be useful indicators for anyone in possession of cherished photographs. First, only low-intensity illumination should be used on photographs: from fifty to three hundred lux —as measured by an appropriate illuminance meter (luxmeter)—with very low ultra-violet (UV) content. The use of light emitting diodes is very promising if the colour rendering index is high enough and the geometry of the lighting is appropriate. Even using low-intensity filtered illumination, photographs cannot be displayed indefinitely since the damaging effects of light are cumulative. Photographs that are particularly light fugitive can only be displayed for short periods of time before being returned to dark storage.
As a result of the collaboration between AXA-Art and the CRCC, light dosimeters designed to estimate the amount of light on photographs whilst they are on display are currently under development. This will be used as an early warning system to indicate when light sensitive artefacts may suffer from over-exposure. Such care makes it possible for future generations to view photographs in something approaching their original condition.
The article is courtesy of AXA Art, sponsors of the AXA Art Research Grant, which is currently supporting the Centre de Recherche sur la Conservation des Collections (CRCC, Paris) and helping to promote the protection of photographic collections.