Mechanisms of antioxidant action: The role of copper salts in the photostabilization of paint media

Verdigris, a copper pigment containing basic copper acetate hydrate, is an effective light stabilizer for linseed oil based paint media but gives rise to discolouration over a long period. The antioxidant process is shown to result in the formation of conjugated chromophores in the medium. A catalytic antioxidant mechanism involving redox reactions of the copper ions is proposed to account for the efficiency of the pigment as a light stabilizer.