Bronze disease

Corrosion of copper and bronze objects caused by the production of copper chlorides, which break down the normally protective surface patinas.

Light blue-green blisters form on the surface. When they are touched, they crumble and fall away leaving a pitted surface. The corrosion is cyclic, setting up reactive and destructive corrosion cells on the surface of the metal.

Corner of a gilded frame showing green brown corrosion