Bronze disease

A corrosion reaction that occurs when moisture and oxygen interact with certain chloride compounds, occasionally found in the corrosion layers of copper-rich metals. This reaction is self-perpetuating, causes pitting in the metal, and produces a powdery, light-green corrosion by-product (see photo).

However, the light green often seen on outdoor bronzes is rarely, if ever, bronze disease, but rather one of the copper sulphate salts. (See 'Paratacamite'.)