Verdigris

{{short description|Green copper-based pigment}} {{Cleanup rewrite|conflating verdigris, patina, copper acetates, and/or copper carbonates|talk=This article is fundamentally flawed|date=February 2026}} {{About|copper(II) acetate, used as a pigment}} {{Infobox color | title=Verdigris | hex=43B3AE | source=[https://www.colorhexa.com/43b3ae] | isccname=Brilliant bluish green }} '''Verdigris''' ({{IPAc-en|ˈ|v|ɜːr|d|ɪ|ɡ|r|iː|(|s|)}})<ref>"Its pronunciation in English is still unsettled" (''Fowler's Dictionary of Modern English Usage'' (4 ed.) edited by: Jeremy Butterfield). The pronunciation /-ɡriːs/ is the first one given by Merriam-Webster's dictionary, but /-ɡriː/ is first in the ''Oxford Dictionary of English'' (3 ed.) (2015).</ref> is a common name for any of a variety of somewhat toxic<ref name="Merriam-Webster Dictionary">{{Cite Merriam-Webster|verdigris}}</ref><ref name="Karmakar-2015">{{cite book |last=Karmakar |first=Rabindra N. |year=2015 |title=Forensic medicine and toxicology: theory, oral & practical |edition=5th |publisher=Academic Publishers |isbn=978-938342054-4 |pages=95–96 |url=https://books.google.com/books?id=xi1jDAAAQBAJ&q=Verdigris }}</ref><ref name="The Lancet-1843">{{Cite journal |date=January 1843|url=https://doi.org/10.1016/S0140-6736(02)76992-4 |journal=The Lancet |volume=39 |issue=1013 |pages=663–664 |doi=10.1016/s0140-6736(02)76992-4 |issn=0140-6736 |title=Poisoning by Verdigris|url-access=subscription }}</ref> copper salts of acetic acid, which range in colour from green to a bluish-green depending on their chemical composition.<ref name="Kühn-1993">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</ref>{{Rp|page=132}} Once used as a medicine<ref name=co>{{Cite web |title=Medical Uses of Copper in Antiquity |url=http://www.copper.org/publications/newsletters/innovations/2000/06/medicine-chest.html |access-date=8 June 2014 |website=Copper Development Association |ref=5}}</ref><ref name=paris>{{Cite book |last=Paris |first=John Ayrton |url=https://www.gutenberg.org/ebooks/62958 |title=Pharmacologia |publisher=W. E. Dean |year=1831 |location=New York |quote=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}}</ref> and pharmaceutical preparation,<ref name="Benhamou-1984">{{Cite journal |last=Benhamou |first=Reed |date=1984 |title=Verdigris and the Entrepreneuse |url=https://www.jstor.org/stable/3104711 |journal=Technology and Culture |volume=25 |issue=2 |pages=171–181 |doi=10.2307/3104711 |jstor=3104711 |s2cid=112614238 |issn=0040-165X|url-access=subscription }}</ref>{{Rp|page=176}}<ref name="De la Roja-2007">{{Cite journal |last1=De la Roja |first1=José Manuel |last2=San Andrés |first2=Margarita |last3=Cubino |first3=Natalia Sancho |last4=Santos-Gómez |first4=Sonia |date=2007 |title=Variations in the colorimetric characteristics of verdigris pictorial films depending on the process used to produce the pigment and the type of binding agent used in applying it |url=http://dx.doi.org/10.1002/col.20311 |journal=Color Research & Application |volume=32 |issue=5 |page=414 |doi=10.1002/col.20311 |issn=0361-2317|url-access=subscription }}</ref> verdigris occurs naturally, creating a patina on copper, bronze, and brass, and is the main component of a historic green pigment used for artistic purposes from antiquity until the late 20th century, including in easel painting, polychromatic sculptures, and illumination of maps.<ref name="De la Roja-2007"/>{{Rp|pages=414–423}}<ref>[http://colourlex.com/project/verdigris/ Verdigris], ColourLex</ref> However, due to its instability, its popularity declined as other green pigments became readily available.<ref name="Benhamou-1984" />{{Rp|page=171}} The instability of its appearance stems from its hydration level and basicity, which change as the pigment interacts with other materials over time.<ref name="Santoro-2014" />{{Rp|page=637}}

== History == [[File:Verdigris.JPG|thumb|Naturally occurring verdigris on exposed metal in the Prague Metro.]] === Etymology === The name ''verdigris'' comes from the Middle English ''{{Lang|enm|vertegrez}}'', from the Old French {{Lang|fro|verte grez}}. According to one view, it comes from ''vert d'aigre'',<ref>{{cite book|first=Henri|id=RC2|last=Dauthenay|location=Paris|page=240|publisher=Librairie horticole|title=Répertoire de couleurs pour aider à la détermination des couleurs des fleurs, des feuillages et des fruits|url=https://gallica.bnf.fr/ark:/12148/bpt6k64453604/f94.image|volume=2|year=1905}}</ref> "green [made by action] of vinegar". The modern French writing of this word is ''{{Lang|fr|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 it is more usually given another etymology as ''vert-de-Grèce'' ("green of Greece").<ref name="StClair">{{Cite book|title=The Secret Lives of Colour|last=St. Clair|first=Kassia|publisher=John Murray|year=2016|isbn=9781473630819|location=London|page=215|oclc=936144129}}</ref><ref>''The Concise Oxford Dictionary of English Etymology'', edited by T. F. Hoad (1996), and Merriam-Webster's dictionary give only this second etymology.</ref>

=== Production === Copper(II) acetate is prepared by treatment of copper(II) hydroxide with acetic acid.<ref name="Solomon-2011" /> The historical methods used for producing verdigris have been recorded in artistic treaties, manuscripts on alchemy, works in natural history, and texts on medicine.<ref name="De la Roja-2007" />{{Rp|page=414}} The most common ingredients used were copper and vinegar. Throughout history, recipes changed. In the Middle Ages, copper strips were attached to a wooden block with acetic acid; the block was then buried in dung. A few weeks later, the block was to be dug up, and the verdigris scraped off.<ref>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.</ref> Another method of production was developed in 18th-century Montpellier, France, a locale which had the ideal climate to produce verdigris for pulverization.<ref name="Benhamou-1984"/>{{Rp|page=177}} The industry there was long dominated by women, with verdigris manufactured in household cellars using copper plates stacked in clay pots that were filled with distilled wine.<ref name="Solomon-2011">{{cite journal |last1=Solomon |first1=Sally D. |last2=Rutkowsky |first2=Susan A. |last3=Mahon |first3=Megan L. |last4=Halpern |first4=Erica M. |year=2011 |title=Synthesis of Copper Pigments, Malachite and Verdigris: Making Tempera Paint |journal=Journal of Chemical Education |volume=88 |issue=12 |pages=1694–1697 |bibcode=2011JChEd..88.1694S |doi=10.1021/ed200096e}}</ref> The acid in the grapes caused the copper to develop crystals. The crystals ripened into verdigris and were scraped off when matured.<ref name="Benhamou-1984" />{{Rp|page=172}} It was a profitable business, and 80% of production was sold abroad through certified female brokers. At the height of its popularity, in the 1710s, the government had to enforce inspection systems to address growing fraudulent practices. By the 20th century, the production of verdigris had moved away from Montpellier and more cost-efficient methods of producing green pigments sent the industry into decline after WWI.<ref name="Benhamou-1984" />{{Rp|pages=179–182}}

== Chemical composition == Verdigris is a collective term for copper acetate, whose chemical varieties produce different hues. The technical literature is inconsistent in describing these variations. Some sources refer to "neutral verdigris" as copper(II) acetate monohydrate ({{chem2|Cu(CH3CO2)2·(H2O)}}) and to "blue verdigris" as {{chem2|Cu(CH3CO2)2·CuO·(H2O)6}}.<ref name="Richardson-2000">{{cite book |last1=Richardson |first1=H. Wayne |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2000 |isbn=3527306730 |chapter=Copper Compounds |doi=10.1002/14356007.a07_567}}</ref> Other sources describe the main copper salt in natural verdigris as {{chem2|Cu4SO4(OH)6}} (brochantite).<ref name="Fitzgerald 1998">{{cite journal |last1=Fitzgerald |first1=K.P. |last2=Nairn |first2=J. |last3=Atrens |first3=A. |year=1998 |title=The chemistry of copper patination |journal=Corrosion Science |volume=40 |issue=12 |pages=2029–2050 |doi=10.1016/s0010-938x(98)00093-6 |bibcode=1998Corro..40.2029F |issn=0010-938X}}</ref> Still, other sources describe it as basic copper carbonate ({{chem2|Cu2CO3(OH)2}}),<ref name="Sharp 1990">Sharp, D. W. A: ''Penguin Dictionary of Chemistry'', page 419. Penguin Books, 1990 (2nd edition)</ref> or as {{chem2|Cu(CH3CO2)2·(Cu(OH)2)_''n''}} where ''n'' varies from 0 to 3.<ref>{{cite journal |last1=Kühn |first1=Hermann |year=1970 |title=Verdigris and Copper Resinate |journal=Studies in Conservation |volume=15 |pages=12–36 |doi=10.1179/sic.1970.15.1.002}}</ref> In marine environments, the main copper salt is tribasic copper chloride ({{chem2|Cu2(OH)3Cl}}).<ref name="Fitzgerald 1998" /><ref name="Sharp 1990" />

Overall, variations of verdigris can be divided into two groups: basic verdigris and neutral verdigris.<ref name="Kühn-1993" />{{Rp|page=132}} The difference in colour depends on the hydration level and degrees of basicity.<ref name="Santoro-2014">{{Cite journal |last1=Santoro |first1=Carlotta |last2=Zarkout |first2=Karim |last3=Le Hô |first3=Anne-Solenn |last4=Mirambet |first4=François |last5=Gourier |first5=Didier |last6=Binet |first6=Laurent |last7=Pagès-Camagna |first7=Sandrine |last8=Reguer |first8=Solenn |last9=Mirabaud |first9=Sigrid |last10=Du |first10=Yann |last11=Griesmar |first11=Pascal |last12=Lubin-Germain |first12=Nadège |last13=Menu |first13=Michel |date=2014-01-29 |title=New highlights on degradation process of verdigris from easel paintings |url=http://dx.doi.org/10.1007/s00339-014-8253-2 |journal=Applied Physics A |volume=114 |issue=3 |pages=637–645 |doi=10.1007/s00339-014-8253-2 |bibcode=2014ApPhA.114..637S |s2cid=253847558 |issn=0947-8396|url-access=subscription }}</ref>{{Rp|page=637}}

=== Toxicity === {{Main|Copper toxicity}} Verdigris, which was once used as a medicine<ref name=co/><ref name=paris/> and pharmaceutical preparation <ref name="Benhamou-1984" />{{Rp|page=176}}<ref name="De la Roja-2007"/>{{Rp|page=414}}{{Clarify span|text=is mildly poisonous.|reason='How' is it poisonous? Inhalation? Contact? Ingestion? Please clarify and expand.|date=February 2024}}<ref name="Merriam-Webster Dictionary" /><ref name="Karmakar-2015" /><ref name="The Lancet-1843" />{{better source needed|reason=Of the four current citations one is a dictionary definition, one is of a non-publicly accessible journal article published in 1843, and two are just bare references to publications inaccessible online.|date=February 2024}} Symptoms of toxicity include nausea, anemia and death, although widespread acquired immunity has been documented, as occurred with female workers in Montpellier.<ref>[https://muse.jhu.edu/pub/3/oa_edited_volume/chapter/3623045/pdf Women and the Verdigris Industry in Montpellier], European Women and Preindustrial Craft. Project MUSE, Indiana University Press, 1995</ref> Nontoxic substitutes have been developed for some applications, such as art pigments.

==Uses== Verdigris is a naturally occurring protective layer on metals such as copper, brass, and bronze. In addition to being a desirable artistic effect, it has been used primarily as a pigment and in now-outdated medicinal preparations.

When burned, verdigris produces a green flame.<ref>{{Cite web |last=Fluke |date=July 7, 2015 |title=Verdigris removal Via firing |url=https://en.numista.com/forum/topic41034.html |access-date=2024-08-03 |website=Numista}}</ref>

===Pigment=== Verdigris has been used as a pigment since antiquity, including in paintings in Rome and Pompeii. The use of verdigris continued into the Middle Ages, Renaissance and Baroque paintings.<ref name="Kühn-1993" />{{Rp|page=132}} It has been identified in ''The Last Supper'' (1306) by Giotto.<ref name="Kühn-1993" />{{Rp|page=142}} During the 15th and 16th centuries, it was used in paintings for its transparency and brilliance.<ref name="Santoro-2014" />{{Rp|page=637}} It was difficult to create strong green colors in paintings due to the limitations of the existing green, yellow and blue pigments. In early Italian, Netherlandish, and German paintings, verdigris was widely used to create pure green tones for landscapes and drapery, such as the green coat of Saint John in the ''Mond Crucifixion'' by Raphael.<ref name="Bette-2017" />{{Rp|page=46}} Verdigris was used as both glaze and opaque paint. When verdigris glaze was combined with lead white or lead-tin yellow, it created a deeply saturated green.<ref name="Kühn-1993" />{{Rp|page=132–136}} It was used in oil-based house paint for French and Dutch country houses. Verdigris also was used as an imitation of 'Chinese varnish' on European lacquer.<ref name="Benhamou-1984" />{{Rp|pages=175–176}} However, during the 19th century, the use of verdigris began to decrease as alternatives such as Emerald Green and viridian became more popular.<ref name="Kühn-1993" />{{Rp|page=132}}

==== Stability ==== As a pigment, verdigris is subject to colour change. The changes are most pronounced during the first month of exposure to air. The changes also depend on the type of binding agent and type of verdigris used. For example, changes are less pronounced with neutral verdigris in oil and egg tempera compared to basic verdigris.<ref name="Kühn-1993" />{{Rp|page=135}} With aging, the green pigment in these applications will show signs of browning or darkening.<ref name="Santoro-2014" />{{Rp|page=637}} For example, in Botticelli's ''The Mystical Nativity'', from 1500, the blue-green costumes of the angels have darkened to a dark green colour.<ref>{{cite book |last1=Bomford |first1=David |title=A Closer Look at Colour |last2=Ashok |first2=Roy |date=2009 |publisher=National Gallery, London |isbn=978-1-85709-442-8 |location=London |pages=38}}</ref>

Verdigris pigment 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.<ref name="StClair" /> The browning mechanism is attributed to the transient formation of Cu(I) in the pigment and oil system. The reduction of Cu(II) into Cu(I) due to the release of a carboxylate, causes changes in the optical properties of pigment. Furthermore, linseed oil induces the transformation of the copper acetate bimetallic structure, and forms monomeric series. Dioxygen that reacts with partially decarboxylated dimers to form a peroxy-Cu dimer complex is responsible for the darkening of the pigment.<ref name="Santoro-2014" />{{Rp|pages=635–638}}

In previous literature on painting, verdigris has been described as unstable when combined with other pigments which leads to further deterioration. Due to the fickle nature of the pigment, it required special preparation of paint, carefully layered application, and immediate sealing with varnish to avoid rapid discoloration (but not in the case of oil paint).<ref name="StClair" /> However, further scientific research suggests that the difficulties are less extreme than previously described. The pigment nonetheless has the ability to degrade cellulosic materials, such as paper.<ref name="Kühn-1993" />{{Rp|page=137}} In terms of identification and reproduction, modern technology and reproducible synthesis procedures have been developed to be used for museums and collections to identify distinct verdigris phases in historical artworks.<ref name="Bette-2017">{{Cite journal |last1=Bette |first1=Sebastian |last2=Kremer |first2=Reinhard K. |last3=Eggert |first3=Gerhard |last4=Tang |first4=Chiu C. |last5=Dinnebier |first5=Robert E. |date=2017 |title=On verdigris, part I: synthesis, crystal structure solution and characterisation of the 1–2–0 phase (Cu₃(CH₃COO)₂(OH)₄) |journal=Dalton Transactions |volume=46 |issue=43 |pages=14847–14858 |doi=10.1039/c7dt03288a |pmid=29043336 |issn=1477-9226|doi-access=free }}</ref>{{Rp|page=14857}} Certain components of historical verdigris pigments, copper(II) acetates, are partially irreproducible based on the given historical recipes.<ref name="Bette-2017" />{{Rp|page=14847}}

{{gallery | height = 200 width = 175 align = center |File:Last Supper (by Giotto di Bondone) - Capella degli Scrovegni (Padova).jpg|One of the earliest uses of verdigris as a pigment in painting; ''Last Supper'' (1306) by Giotto Di Bondone |File:CrocefissioneRaffaello.jpg|Raphael used verdigris for the green coat of Saint John, the left angel's frock, and other accents, in ''The Mond Crucifixion''. |File:Sandro botticelli, natività mistica, 1500, 02 angeli.jpg|The Verdigris of the angels' costumes in ''Nativita Mistica'' by Botticelli darkened from bluish green to foliage green. }}

=== Medicine=== Verdigris has also been used in medicine,<ref name=co/><ref name=paris/> and is identified in the ''Pharmacologia'' of John Ayrton Paris as the healing rust of the Spear of Telephus mentioned by Homer.<ref name=co/><ref name=paris/> Verdigris solids were also used for pharmaceutical preparations<ref name="De la Roja-2007"/>{{Rp|page=414}} in the 18th century to treat canker sores.<ref name="Benhamou-1984"/>{{Rp|page=176}}

==See also== * Bronze disease * Green pigments * List of colors * List of inorganic pigments * Patina

==References== <references/>

==External links== {{Wiktionary}} * [https://www.dcceew.gov.au/environment/protection/npi/substances/fact-sheets/copper-and-compounds National Pollutant Inventory – Copper and compounds fact sheet] * [https://colourlex.com/project/verdigris/ Verdigris], ColourLex * [http://www.grosse.is-a-geek.com/paintings_pigments-2.html Making Pigments – Verdigris], Paul Grosse

{{Shades of cyan}}

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Category:Pigments Category:Inorganic pigments Category:Copper(II) compounds Category:Alchemical substances Category:Shades of cyan Category:Shades of green