Patinas can also be found in woks or other metal baking dishes, which form when properly seasoned. 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 needs special conditions to work as intended. Patina is also found on slip rings and commutators. The dark color of the statue made English sailors call the square that houses it "Black Horse Square".
The same statue in 2015, after removal of the patina (2012–13), showing the original 1775 finish. This patina is water-soluble and will not last on the outside of a building like a "true" patina. A patina can be produced on copper by the application of vinegar ( acetic acid).
More simply, the French sculptor Auguste Rodin used to instruct assistants at his studio to urinate over bronzes stored in the outside yard. Sometimes the surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats. Some patina colors are achieved by the mixing of colors from the reaction with the metal surface with pigments added to the chemicals. Colors range from matte sandstone yellow to deep blues, greens, whites, reds, and various blacks. For artworks, patination is often deliberately accelerated by applying chemicals with heat. 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). For copper alloys, such as bronze, exposure to chlorides leads to green, while sulfur compounds (such as " liver of sulfur") tend to brown. Patination composition varies with the reacted elements and these will determine the color of the patina. They are often used by artists as surface embellishments either for color, texture, or both. The process is often called distressing.Ī wide range of chemicals, both household and commercial, can give a variety of patinas. See also: Copper in architecture § FinishesĪrtists and metalworkers often deliberately add patinas as a part of the original design and decoration of art and furniture, or to simulate antiquity in newly made objects. The chemical process by which a patina forms or is deliberately induced is called patination, and a work of art coated by a patina is said to be patinated. Figuratively, patina can refer to any fading, darkening, or other signs of age, which are felt to be natural or unavoidable (or both). The word patina comes from the Italian patina (shallow layer of deposit on a surface), derived from the Latin patĭna (pan, shallow dish). It also refers to development as the result of weathering of a case-hardened layer, called cortex by geologists, within the surface of either a flint or chert nodule. In geology and geomorphology, the term patina is used to refer to discolored film or thin outer layer produced either on or within the surface of a rock or other material by either the development of a weathering rind within the surface of a rock, the formation of desert varnish on the surface of a rock, or combination of both. This has led stone tool analysts in recent times to generally prefer the term cortification as a better term to describe the process than patination. Īrchaeologists also use the term patina to refer to a corticated layer that develops over time that is due to a range of complex factors on flint tools and ancient stone monuments. Patina also refers to accumulated changes in surface texture and color that result from normal use of an object such as a coin or a piece of furniture over time. In common parlance, weathering rust on steel is often mistakenly referred to as patina. On metal, patina is a coating of various chemical compounds such as oxides, carbonates, sulfides, or sulfates formed on the surface during exposure to atmospheric elements ( oxygen, rain, acid rain, carbon dioxide, sulfur-bearing compounds).
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