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Verdigris is the common name for
blue-green Blue-green is the color that is between green and blue. It belongs to the cyan family of colors. Variations Cyan (aqua) Cyan, also called aqua, is the blue-green color that is between blue and green on a modern RGB color wheel. The ...
,
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
-based
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
s that form a patina on copper, bronze, and
brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...
. The technical literature is ambiguous as to its chemical composition. Some sources refer to "neutral verdigris" as
copper(II) acetate Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is availab ...
mono hydrate () and to "blue verdigris" as . Another source describes it as a
basic copper carbonate Basic copper carbonate is a chemical compound, more properly called copper(II) carbonate hydroxide. It is an ionic compound (a salt) consisting of the ions copper(II) , carbonate , and hydroxide . The name most commonly refers to the compound w ...
(()2), and, when near the sea, basic copper chloride (Cu2(OH)3Cl). Still other sources describe verdigris as .(Cu(OH)2)n where n varies from 0 to 3. The
alchemical symbol Alchemical symbols, originally devised as part of alchemy, were used to denote some elements and some compounds until the 18th century. Although notation like this was mostly standardized, style and symbol varied between alchemists, so this pag ...
for verdigris is 🜨 (unicode U+1F728).


Etymology

The name ''verdigris'' comes from the
Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English ...
''vertegrez'', from the
Old French Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intellig ...
''verte grez'', meaning ''vert d'aigre'', "green ade by action ofvinegar". The modern French writing of this word is ''vert-de-gris'' ("green of grey"), sounding like the older name ''verdet gris'' ("grey greenish"), itself a deformation of ''verte grez''. It was used as a pigment in paintings and other art objects (as green color), mostly imported from Greece, and hence ''verte grez'' is also given another etymology as ''vert-de-Grèce'' ("green of
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders ...
").


Manufacture

A variety of recipes have been described for obtaining this blue-green patina on copper,
brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...
, or bronze. It was originally made by hanging copper plates over hot
vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to eth ...
in a sealed pot until a green crust formed on the copper. Another method, used in the Middle Ages, was to attach copper strips to a wooden block with acetic acid, then bury the sealed block in dung. A few weeks later, the block was to be dug up, and the verdigris scraped off. In eighteenth-century Montpellier,
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
, it was manufactured in household cellars, "where copper plates were stacked in clay pots filled with distilled wine." The verdigris was scraped off weekly by the women of the household. Copper(II) acetate is prepared by treatment of copper(II) hydroxide with acetic acid.


Uses


Pigment

The vivid green color of copper(II) acetate made this form of verdigris a much used
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
. Until the 19th century, verdigris was the most vibrant green pigment available and was frequently used in painting. Verdigris is lightfast in oil paint, as numerous examples of 15th-century paintings show. However, its lightfastness and air resistance are very low in other media. Copper resinate, made from verdigris by boiling it in a
resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
, is not lightfast, even in oil paint. In the presence of light and air, green copper resinate becomes stable brown copper oxide. This degradation is to blame for the brown or bronze color of grass or foliage in many old paintings, although not typically those of the Early Netherlandish painters such as Jan van Eyck, who often used normal verdigris. In addition, verdigris is a fickle pigment requiring special preparation of paint, careful layered application and immediate sealing with varnish to avoid rapid discoloration (but not in the case of oil paint). Verdigris has the curious property in oil painting that it is initially bluish-green, but turns a rich foliage green over the course of about a month. A painting by Botticelli, The Mystical Nativity, from 1500, shows a group of angels whose blue-green costumes have discolored to a dark green. Verdigris fell out of use by artists as more stable green pigments became available.


Other

Copper compounds are used as fungicides (''
The Merck Index ''The Merck Index'' is an encyclopedia of chemicals, drugs and biologicals with over 10,000 monograph on single substances or groups of related compounds published online by the Royal Society of Chemistry. History The first edition of the M ...
'', Ninth Ed., 1976). Verdigris has also been used in medicine and is identified in the ''Pharmacologia'' of John Ayrton Paris as the healing rust of the Spear of
Telephus In Greek mythology, Telephus (; grc-gre, Τήλεφος, ''Tēlephos'', "far-shining") was the son of Heracles and Auge, who was the daughter of king Aleus of Tegea. He was adopted by Teuthras, the king of Mysia, in Asia Minor, whom he succe ...
as mentioned by
Homer Homer (; grc, Ὅμηρος , ''Hómēros'') (born ) was a Greek poet who is credited as the author of the ''Iliad'' and the ''Odyssey'', two epic poems that are foundational works of ancient Greek literature. Homer is considered one of the ...
. A compound containing beeswax, kidney fat, and verdigris was used in medieval times in the fletching of arrows.


See also

*
Bronze disease Bronze disease is an irreversible and nearly inexorable corrosion process that occurs when chlorides come into contact with bronze or other copper-bearing alloys. It can occur as both a dark green coating, or as a much lighter whitish fuzzy or ...
* Green pigments *
List of colors These are the lists of colors; * List of colors: A–F * List of colors: G–M * List of colors: N–Z * List of colors (compact) * List of colors by shade * List of color palettes * List of Crayola crayon colors * List of RAL colors * List of X ...
*
List of inorganic pigments The following list includes commercially or artistically important inorganic pigments of natural and synthetic origin.. Purple pigments Aluminum pigments * Ultramarine violet: (PV15) - a synthetic or naturally occurring sulfur containing silica ...
* Patina


References


External links


National Pollutant Inventory - Copper and compounds fact sheet

Verdigris
ColourLex

Paul Grosse {{Shades of cyan Pigments Organic pigments Copper(II) compounds Alchemical substances Shades of cyan Shades of green