The Characterization of Cobalt Violet Pigments

The study of several commercial paints and dry pigments, as well as paint samples removed from works of art, allowed the identification of magnesium cobalt arsenate, a pigment that has not previously been reported in the literature. This article focuses on the composition, characterization and occurrences of this pigment as well as other violet cobalt compounds used as artists' pigments, namely cobalt phosphate, cobalt phosphate octahydrate, ammonium cobalt phosphate hydrate and lithium cobalt phosphate. Cobalt arsenate, a pigment frequently mentioned in the literature on artists' materials, has not yet been unambiguously identified. The introduction of these compounds as pigments is briefly discussed.