verdigris [key], one of three copper acetates: blue verdigris, Cu(CH3COO)2·CuO·6H2O; green verdigris, 2Cu(CH3COO)2·CuO·6H2O; or neutral verdigris, Cu(CH3COO)2·H2O; or a mixture of them. It is a poisonous gray-green to green-blue substance that is formed by the action of acetic acid on copper or copper oxide, e.g., verdigris can form on copper pots used to cook acidic foods such as tomatoes. Verdigris is used as a mordant in dyeing, as a pigment, and in making Paris green. Verdigris may also be used to mean patina.
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