Patina

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A bronze coin of the Han Dynasty - circa 1st century BC with green patina.

Patina is a chemical compound formed on the surface of metal. Patinas form on metal from exposure to the elements. They are often deliberately added by artists and metalworkers. Patinas may be used to 'antique' objects, as a part of the design or decoration of art and furniture.

Patinas are restricted to exposed surfaces and can flake off. One reason bronze is so highly valued in statuary is that its patina protects it against further corrosion. This natural patina seldom shows a tendency to flake. Brass is also resistant to corrosion, but it is, in the long run, not as attractive since local pitting shows against the shiny background.

Figuratively, patina can refer to any fading, darkening or other signs of age, which are felt to be natural and/or unavoidable.

The chemical process by which a patina forms is called patination, and a work of art coated by a patina is said to be patinated.

One example of a patina is a green surface texture created by slow chemical alteration of copper, producing a basic carbonate. It can form on pure copper objects as well as alloys which contain copper, such as bronze or brass.

The Statue of Liberty gets its green color from the natural patina formed on its copper surface.

A wide range of chemicals, both household and commercial, can give a variety of patinas. They are often used by artists as surface embellishments either for color, texture, or both.

Patina is also found on slip rings and commutators. This type of patina is formed by corrosion, what elements the air might hold, residue from the wear of the carbon brush and moisture; thus, the patina need special conditions to work as intended.

Patinas can also be found in woks, which form when properly seasoned. The patina on a wok is a dark coating of oils that have been burned onto it to prevent food sticking and to enhance the flavor of the foods cooked in it. Steaming foods or using soap on a wok could damage the patina and possibly allow the wok to rust.

In terms of antiques, "Patina is everything that happens to an object over the course of time. The nick in the leg of a table, a scratch on a table top, the loss of moisture in the paint, the crackling of a finish or a glaze in ceramics, the gentle wear patterns on the edge of a plate. All these things add up to create a softer look, subtle color changes, a character. Patina is built from all the effects, natural and man-made, that create a true antique." - Israel Sack

In this cast bronze sculpture, Balance by David Ascalon, reactive chemicals were applied to the metallic surface to create an intentional surface patina (in this case, a marbleized blue).

The splash pattern from "instant" patination by highly reactive chemicals is visible on this brass surface by Stoller Metals. [1]

Footprint by artist Pam Glew [2] - The footprint shows the copper beneath a layer of oxidised copper patination. The effect was made by the application of chemicals to the copper canvas