Everything about Patina totally explained
Patina is a coating of various chemical compounds such as
oxides or
carbonates formed on the surface of metal during exposure to
weathering. The green patina that forms naturally on copper and bronze is known as
verdigris and consists of copper carbonate. Patina also refers to accumulated changes in surface texture and colour that result from normal use of an object such as a coin or a piece of furniture. Artists 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.
Patinas are restricted to exposed surfaces and can flake off. One reason bronze is so highly valued in statuary is that its patina protects or
passivates 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.
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. Patination composition varies with the reacted elements and these will determine the color of the patina. Exposure to chlorides leads to green, while sulfur compounds (such as "
liver of sulfur") tend to brown. For artworks patination is deliberately accelerated by heat. Colors range from matte sandstone yellow to deep blues, reds and various blacks, sometimes with the surface sheen enhanced by waxing for artwork displayed indoors.
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
Image: David Ascalon_-_Balance.jpg|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).
Image: Patinated_Brass.jpg|The splash pattern from "instant" patination by highly reactive chemicals is visible on this brass surface by Stoller Metals. (External Link
)
Image: footprint-wiki.jpg|Footprint by artist Pam Glew (External Link
) - The footprint shows the copper beneath a layer of copper carbonate patination. The effect was made by the application of chemicals to the copper canvas.
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