Verdigris

Another name for the green patina that forms on the surface of copper.

Verdigris is the common name for the green coating or patina formed when copper, brass or bronze is weathered and exposed to air or seawater over a period of time. It is usually a basic copper carbonate, but near the sea will be a basic copper chloride. If acetic acid is present at the time of weathering, it may consist of copper(II) acetate.