Predicting light fading

We all know the damage that light can cause to organic objects, and we also know a great deal about why it happens, but predicting how fast that damage will occur is an issue conservators continue to grapple with. The Blue Wool standards (a method whereby the empirically measured fading of blue dyes in wool can be used as a reference point for measuring fading) help to inform conservators on the light sensitiveness of objects. They in turn can then advise curators on the regularity of turnover of these objects whilst on exhibition. This of course is about limiting exposure to light (and thus damage), not about reversing that damage. There continues to be a myth that by 'resting' light sensitive material, such as watercolours, their colour can miraculously be restored.

These changeovers of light sensitive objects can add an enormous cost to a ‘permanent’ exhibition (life span of say 8 years). The National Museum of Australia has estimated that each changeover costs about $1,000 per object, by the time that conservation, relabeling, and installation is taken into account. Change objects every two years over an eight year exhibition span, and the NMA have calculated that in some object rich exhibitions, the changeovers can cost many hundreds of thousands of dollars.

So it was exciting to hear a couple of papers by Bruce Ford at the recent AICCM (Australian Institute for the Conservation of Cultural Material) conference in Fremantle, WA on work he is undertaking for the NMA to try and more accurately calculate the rate of fade, and thus pragmatically reduce the high cost of the change-over of light sensitive objects. NMA has acquired an Oriel Micro fading test system which is providing the relevant data. Basically the system blasts a vast amount of light (c 10 million lux) at a tiny spot, smaller than a printed full stop. Because the light is so intense it can replicate about 10 years display at 50 lux for 8 hours a day in 10 minutes. But by doing it on an actual element of the artwork, but in such a small area that the eye cannot read the damage caused, it allows for much more accurate understanding of the rate of fade.

And the results are clearly showing that while some objects are more vulnerable to light than previously assumed, conservators have vastly overestimated light sensitivity. The result is that light levels and exhibition durations have been unnecessarily restricted and curators saddled with the difficult task of finding and interpreting suitable replacements mid exhibition.

Salutary stuff and one that will have a big impact on future planning for exhibitions and their maintenance budgets.