Abstract The incorporation of gas black, ferric oxide, and lead titanate, which absorb actinic rays, into rubber-sulfur ebonites did not reduce the rate of electrical surface deterioration appreciably. It increased the final equilibrium resistivity, but not sufficiently for the increase to be of much practical value. This result confirms the conclusion from a study of the mechanism of surface deterioration that a light-absorbent pigment is unlikely to be effective in retarding deterioration because its particles are relatively large and far apart in comparison with the thickness of the surface layer responsible for the deterioration. The use of the mercury-vapor lamp causes a more rapid deterioration than daylight, but does not appear to alter the order in which the samples range themselves.