The deterioration of cadmium sulphide yellow artists' pigments

This paper investigates the deterioration of cadmium sulphide yellow pigments, through analysis of artificially aged pigments and samples from 12 paintings. The deterioration occurs mainly in the lighter zinccontaining yellows and leads to discolouration and loss of adhesion within the paint, resulting in a chalking and crumbly surface. Samples were characterized using light/ultraviolet and electron microscopy/energy dispersive X-ray (EDX) spectroscopy and X-raydiffraction. Darkening of yellow paint was characterized by the formation of brown cadmium oxide at the surface of some samples, while the formation of colourless/white products including cadmium sulphate and zinc hydroxide, and the degradation of the oil bindingmedium, is associated with chalking. A hypothesis is suggested involving the oxidation of cadmium zinc sulphide. The cause of instability may be linked with early manufacturing methods, where the product is largely amorphous.