Information from the Getty AAT
Pigment composed of basic copper acetate and having a dark bluish-green color. Verdigris has been manufactured since ancient times by placing copper plates over vats of fermenting grape skins; the acetic acid quickly reacts to form basic copper acetate. When used directly as a pigment, it discolors from green to black in oil paints, fades in watercolor paints, and reacts with a paper support. It is used to make copper resinate, as a drier for linseed oil, to dye fabrics, and as a colorant and fungicide in antifouling paints.