The word Patina is used to describe the thin blueish-green film that forms on copper and bronze sculptures. It is a result of the oxidation of the copper due to natural weathering.

The word "patina" comes from the Latin word meaning  "shallow dish". The word patina can actually refer to any fading, darkening or other signs of age, which are felt to be natural or unavoidable. The chemical process by which a patina forms is called patination, and a sculpture coated by a patina is said to be patinated.

Perhaps the most well known example of a patinated sculpture is the Statue of Liberty, which appears light green.

A patina is sometimes a desired effect on a new sculptural work and various chemical treatments and specialist coatings are available to induce colored patinas on new metal, and it is often imitated in antiquing and painting techniques for home decor items too.

If you have an antique sculpture with a patina, do not be tempted to polish it off, you may actually be reducing it's value by doing this as collectors look for this as a part of a their valuation process.