Patina

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Patina

Patina ('pa t? n?) is a film on the surface of bronze

Bronze

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive, but sometimes with other chemical element such as phosphorus, manganese, aluminium, or silicon....
or similar metals (produced by oxidation over a long period); a sheen on wooden furniture

Furniture

Furniture is the mass noun for the movable objects which may support the human body , provide storage, or hold objects on horizontal surfaces above the ground....
produced by age, wear, and polishing; or any such acquired change of a surface through age and exposure. On metal, patina is a coating of various chemical compounds such as oxide

Oxide

An oxide is a chemical compound contaning at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides....
s or carbonate

Carbonate

In chemistry, a carbonate is a salt or ester of carbonic acid....
s formed on the surface during exposure to the elements (weathering

Weathering

Weathering is the decomposition of earth Rock , soils and their minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind, and gravity....
). Patina also refers to accumulated changes in surface texture and colour that result from normal use of an object such as a coin

Coin

A coin is a piece of hard material, usually metal or a metallic material, usually in the shape of a Disk , and most often issued by a government....
or a piece of furniture over time.

nas are restricted to exposed surfaces and are fragile (that is, they can flake off).

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Advantages

Patinas are restricted to exposed surfaces and are fragile (that is, they can flake off). One reason bronze is so highly valued in statuary is that its patina protects or passivates

Passivation

Passivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and peroxide alternating with deionized water....
it against further corrosion

Corrosion

Corrosion means the breaking down of essential properties in a material due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen....
. This natural patina is solid and seldom shows a tendency to flake. Brass

Brass

Brass is any alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties. In comparison, bronze is principally an alloy of copper and tin....
is also resistant to corrosion, but it is, in the long run, not as attractive since local pitting shows against the shiny background.

Etymology

The word "patina" is pronounced PAT'n-uh (although puh-TEE-nuh has come into common use in the U.S.), and comes from the Latin for "shallow dish". 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.

Acquired patina

The green patina that forms naturally on copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....
and bronze

Bronze

Verdigris

Verdigris is the common name for the green coating or patina formed when copper, brass or bronze is weathered and exposed to air or seawater over a period of time....
and consists of copper carbonate.

One example of a patina is a green surface texture created by slow chemical alteration of copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29.It is a ductile metal with very high thermal and electrical conductivity....
, producing a basic

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
carbonate. It can form on pure copper objects as well as alloy

Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
s which contain copper, such as bronze

Bronze

Brass

Applied patina

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.

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

Potassium sulfide

Potassium sulfide is the chemical compound with the formula K2S. It is an inorganic polymer with the "antifluorite structure," which means that the small K+ ions occupy the tetrahedral sites in fluorite, and the larger S2- centers occupy the eight-coordinate sites....
") 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 ring

Slip ring

A slip ring is a method of making an electricity connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels or electrical rotary joints, are commonly found in electrical generators for alternating current systems and alternators and in packaging machinery,...
s and commutator

Commutator (electric)

A commutator is an electricity switch that periodically reverses the Current direction in an electric motor or electrical generator. A commutator is a common feature of direct current rotating machines....
s. 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 or other metal baking dishes, 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 or other dish ware could damage the patina and possibly allow rust.

Value

Apart from the aesthetic appearance and practical protection of patination, antique experts confirm that an object's value increases when its patination is intact because it is an important effect of the ageing process and this evidential history is reflected in the value of the piece.

In terms of antiques then,

Repatination

In the case of antiques, several views are held on the value of patination and its replacement if damaged: repatination.

Preserving a piece's look and character is important and removal or reduction may dramatically reduce its value though if patination has flaked off repatination may be recommended.

Appraiser, Reyne Haines notes that "a repatinated metal piece will be worth more than one with major imperfections in the patina," but less than a piece still with its original finish.

Patina

Advantages

Etymology

Acquired patina

Applied patina

Value

Repatination

Gallery

Further reading