Patina is also found on slip rings and commutators. More simply the French sculptor Auguste Rodin used to instruct assistants at his studio to urinate over bronzes stored in the outside yard to get the final effect he wanted, but there is no more real need to do that in modern times.Ī patina can be produced on copper by the application of vinegar (acetic acid) and this patina will be water-soluble and will not last on the outside of a building like a “true” patina, that’s why It is usually used as pigment. Sometimes the surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats. Some patina colours are achieved by the mixing of colors from the reaction with the metal surface with pigments added to the chemicals.
The basic palette for patinas on copper alloys includes chemicals like ammonium sulfide (blue-black), liver of sulfur (brown-black), cupric nitrate (blue-green) and ferric nitrate (yellow-brown).įor artworks, patination is often deliberately accelerated by applying chemicals with heat.Ĭolors range from matte sandstone yellow to deep blues, greens, whites, reds and various blacks. Patination composition varies with the reacted elements and these will determine the color of the patina: for copper alloys, such as bronze, exposure to chlorides leads to green, while sulfur compounds (such as “liver of sulfur”) tend to brown.
They are often used by artists as surface embellishments either for color, texture, or both.
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