Patina
From Free net encyclopedia
Patina is a chemical compound formed on the surface of metal. Patinas form on metal from exposure to the elements, and they are deliberately added by artists and metalworkers.
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 would, in the long run, not be as attractive, as local pitting would show against a 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.
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.
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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, moisture, and need special conditions to work as intended.