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Verdigris is the common name for blue-green, poisonous,[1][2][3] copper-based pigments that form a patina on copper, bronze, and brass. The technical literature is ambiguous as to its chemical composition. Some sources refer to "neutral verdigris" as copper(II) acetate monohydrate (Cu(CH3CO2)2·(H2O)) and to "blue verdigris" as Cu(CH3CO2)2·CuO·(H2O)6.[4] Another source describes it as a basic copper carbonate (Cu
2CO
3(OH)2), and, when near the sea, basic copper chloride (Cu2(OH)3Cl).[5] Still other sources describe verdigris as Cu(CH3CO2)2.(Cu(OH)2)n where n varies from 0 to 3.[6] The alchemical symbol for verdigris is 🜨 (unicode U+1F728).

History

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The name verdigris comes from the Middle English vertegrez, from the Old French verte grez, meaning vert d'aigre,[7] "green [made by action of] vinegar". 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").[8]

Manufacture

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A variety of recipes have been described for obtaining this blue-green patina on copper, brass, or bronze.[9] It was originally made by hanging copper plates over hot vinegar in a sealed pot until a green crust formed on the copper.[8] Another method, used in the Middle Ages, was to attach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, 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.[10] Copper(II) acetate is prepared by treatment of copper(II) hydroxide with acetic acid.[11]

Uses

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Pigment

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The Verdigris of the angels' costumes in "Nativita Mistica" by Botticelli (1500) darkened from bluish green to foliage green.
 
Verdigris in Prague Underground
 
Verdigris on The Spirit of Detroit

The vivid green color of copper(II) acetate made this form of verdigris a much used pigment. Until the 19th century, verdigris was the most vibrant green pigment available and was frequently used in painting.[12][13] 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, is not lightfast, even in oil paint. In the presence of light and air, green copper resinate becomes stable brown copper oxide.[8]

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).[8] 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.[14]

Verdigris fell out of use by artists as more stable green pigments became available.[citation needed]

Other

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Copper compounds are used as fungicides (The Merck Index , Ninth Ed., 1976). Verdigris has also been used in medicine[15] and is identified in the Pharmacologia of John Ayrton Paris as the healing rust of the Spear of Telephus as mentioned by Homer.[16]

A compound containing beeswax, kidney fat, and verdigris was used in medieval times in the fletching of arrows.[citation needed]

  1. ^ "Verigris". Merriam-Webster.com Dictionary. Merriam-Webster.
  2. ^ Karmakar, Rabindra N. (2015). Forensic medicine and toxicology: theory, oral & practical. Academic Publishers.
  3. ^ Anant, Jagdish Kumar, S. R. Inchulkar, and Sangeeta Bhagat (2018). "An overview of copper toxicity relevance to public health." EJPMR 5, no. 11 : 236.
  4. ^ Richardson, H. Wayne (2000). "Copper Compounds". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a07_567. ISBN 3527306730.
  5. ^ Sharp, D. W. A: Penguin Dictionary of Chemistry, page 419. Penguin Books, 1990 (2nd edition)
  6. ^ Kühn, Hermann (1970). "Verdigris and Copper Resinate". Studies in Conservation. 15: 12–36. doi:10.1179/sic.1970.15.1.002.
  7. ^ Dauthenay, Henri (1905). Répertoire de couleurs pour aider à la détermination des couleurs des fleurs, des feuillages et des fruits. Vol. 2. Paris: Librairie horticole. p. 240. RC2.{{cite book}}: CS1 maint: date and year (link)
  8. ^ a b c d St. Clair, Kassia (2016). The Secret Lives of Colour. London: John Murray. p. 215. ISBN 9781473630819. OCLC 936144129.
  9. ^ Helmenstine, Annie Marie (August 26, 2020). "Why Is the Statue of Liberty Green?". ThoughtCo. Retrieved 2021-03-02.
  10. ^ Darnton, Robert. "A Bourgeois Puts His World in Order" in The Great Cat Massacre --and other Episodes in French Cultural History. New York: Vintage Books, 1985. p. 114.
  11. ^ Solomon, Sally D.; Rutkowsky, Susan A.; Mahon, Megan L.; Halpern, Erica M. (2011). "Synthesis of Copper Pigments, Malachite and Verdigris: Making Tempera Paint". Journal of Chemical Education. 88 (12): 1694–1697. Bibcode:2011JChEd..88.1694S. doi:10.1021/ed200096e.
  12. ^ H. Kühn, Verdigris and Copper Resinate, in Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 2: A. Roy (Ed.) Oxford University Press 1993, p. 131 – 158
  13. ^ Verdigris, ColourLex
  14. ^ Bomford, David; Ashok, Roy (2009). A Closer Look at Colour. London: National Gallery, London. p. 38. ISBN 978-1-85709-442-8.
  15. ^ "Medical Uses of Copper in Antiquity". Copper Development Association. Retrieved 8 June 2014.
  16. ^ Paris, John Ayrton (1831). Pharmacologia. New York: W. E. Dean. The rust of the spear of Telephus, mentioned in Homer as a cure for the wounds which that weapon inflicted, was probably Verdegris, and led to the discovery of its use as a surgical application
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