A simple infrared sodium chloride disc technique 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 conven-tional pigmented paint media. The sodium chloride disc technique constitutes an accelerated environmental aging test which can be used to predict the effects of pigments and their wave-length sensitivity on the physical deterioration of the medium. 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 wave-length is not in itself a satisfactory solution to conservation of old paint media.