Artworks

Patina

A patina is a thin layer that forms on the surface of copper, brass, bronze, and similar metals and alloys through age and exposure. Patinas can also provide a protective covering to materials that would otherwise be damaged by corrosion or further weathering.

The green patina that forms naturally on copper and bronze, sometimes called verdigris, usually consists of varying mixtures of copper chlorides, sulfides, sulfates, and carbonates, depending upon environmental conditions such as sulfur-containing acid rain. In clean air rural environments, the patina is created by the slow chemical reaction of copper with carbon dioxide and water, producing a basic copper carbonate. In industrial and urban air environments containing sulfurous acid rain from coal-fired power plants or industrial processes, the final patina is primarily composed of sulphide or sulphate compounds.