A blue-green powder, which consists of basic copper (II) acetate. It is
made by pickling copper in acetic
acid and is used as a pigment and a
mordant in dyeing. The term is also applied
to the blue-green coating, or patina, that exposed copper acquires in air
over a period of time. It is usually a basic copper carbonate, but near
the sea will be a basic copper chloride.