Copper rust, also known as copper oxide, is a common form of corrosion that occurs when copper is exposed to oxygen and moisture. It is characterized by a greenish-blue or bluish-green color. The two most common forms of copper rust are VERDIGRIS (9 letters) and PATINA (6 letters). VERDIGRIS is a powdery, greenish-blue substance that forms on the surface of copper when it is exposed to air and moisture. PATINA is a thin layer of oxidation that forms on the surface of copper over time, giving it a distinctive greenish-brown color. Both VERDIGRIS and PATINA are forms of copper rust and are often used to give copper objects an aged, antique look.