Patina is a coating of various chemical compouns such as oxides or carbonates formed on the surface of metal during exposure to weathering. The green patina that forms naturally on copper and bronze is known as verdigris and consists of copper carbonate. Patina also refers to accumulated changes in surface texture and colour that result from normal use of an object such as a coin or a piece of furniture. Artists and metalworkers often deliberately add patinas as a part of the original design and decoration of art and furniture, or to simulate antiquity in newly-made objects.