Patina is a thin layer that variously forms on the surface of copper, bronze and similar

metals (tarnish produced by oxidation or other chemical processes), or certain stones, and

wooden furniture (sheen produced by age, wear, and polishing), or any similar acquired

change of a surface through age and exposure.

A patina layer takes many years to develop under natural weathering. Buildings in damp

coastal/marine environments will develop patina layers faster than ones in dry inland areas.

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.