The effects of some common pigments on the photo-oxidation of linseed oil-based paint media

A simple infrared, sodium chloride disc technique is described which monitors the loss of binder in a paint medium. The early stages of this process correlate both with oxygen absorption measurements and with the formation of scission products (dicarboxylic acid half esters) by GLC in conventional pigmented paint media. The sodium chloride disc technique constitutes an accelerated environmental ageing test which can be used to predict the effects of pigments and their wavelength sensitivity on the physical deterioration of the medium. It is found that vermilion, one of the more effective photo-sensitizers for photo-oxidation, is relatively insensitive to wavelength variation in the diffuse daylight region and it is concluded that physical screening of the near UV wavelength is not in itself a satisfactory solution to conservation of old paint media.