Chemical Reactions Between Copper Pigments and Oleoresinous Media

study demonstrates that resin and fatty acids are able to extract copper(II) ions from verdigris (copper acetate) and verditer (basic copper carbonate). Ligand exchange reactions of basic copper carbonate with fatty acids and resin acids are much slower than is the case with copper acetate. The browning of paint layers is closely correlated with the relative ease of copper extraction; the copper diffuses in the form of fatty acid or resin carboxylic acid complexes. These complexes are formed in the painting layer during grinding of the pigment with binding media containing oleoresin acids, as well as being formed at the interface of this layer and organic upper layers, such as varnishes.