Verdigris is a common name for any of a variety of somewhat poisonousKarmakar, Rabindra N. (2015). Forensic medicine and toxicology: theory, oral & practical. Academic Publishers.Anant, Jagdish Kumar, S. R. Inchulkar, and Sangeeta Bhagat (2018). "An overview of copper toxicity relevance to public health." EJPMR 5, no. 11 : 236. copper

salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

, which range in colour from green to a bluish-green depending on their chemical composition.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 Once used as a medicine and pharmaceutical preparation, verdigris occurs naturally, creating a

patina Patina ( or ) is a thin layer that variously forms on the surface of copper, brass, bronze and similar metals and metal alloys (tarnish produced by oxidation or other chemical processes) or certain stones and wooden furniture (sheen produced b ...

on copper,

bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...

, 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 with ...

, and is the main component of a historic

green pigment Varieties of the color green may differ in hue, chroma (also called saturation or intensity) or lightness (or value, tone, or brightness), or in two or three of these qualities. Variations in value are also called tints and shades, a tint be ...

used for artistic purposes from antiquity until the late 20th century, including in

easel painting An easel is an upright support used for displaying and/or fixing something resting upon it, at an angle of about 20° to the vertical. In particular, easels are traditionally used by painters to support a painting while they work on it, normally ...

, polychromatic sculptures, and illumination of maps. However, due to its instability, its popularity declined as other green pigments became readily available. The instability of its appearance stems from its hydration level and

basicity In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rou ...

, which change as the pigment interacts with other materials over time.

History

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 p ...

', 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 intelligib ...

. According to one view, it comes from ''vert d'aigre'', "green ade by actionof vinegar". The modern French writing of this word is ' ("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 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 with ...

").

Production

Copper(II) acetate is prepared by treatment of

copper(II) hydroxide Copper(II) hydroxide is the hydroxide of copper with the chemical formula of Cu(OH)2. It is a pale greenish blue or bluish green solid. Some forms of copper(II) hydroxide are sold as "stabilized" copper(II) hydroxide, although they likely consist ...

with

. The historical methods used for producing verdigris have been recorded in artistic treaties,

manuscript A manuscript (abbreviated MS for singular and MSS for plural) was, traditionally, any document written by hand – or, once practical typewriters became available, typewritten – as opposed to mechanically printing, printed or repr ...

s on alchemy, works in natural history, and texts on medicine. The most common ingredients used were copper and vinegar. Throughout history, recipes changed. In the

Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...

, 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. Another method of production was developed in 18th-century

Montpellier Montpellier (, , ; oc, Montpelhièr ) is a city in southern France near the Mediterranean Sea. One of the largest urban centres in the region of Occitania (administrative region), Occitania, Montpellier is the prefecture of the Departments of ...

, France, a locale which had the ideal climate to produce verdigris for pulverization. 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 Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating ...

wine. The acid in the grapes caused the copper to develop crystals. The crystals ripened into verdigris and were scraped off when matured. 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 World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

Chemical composition

Anatoli Boukreev Memorial at Annapurna Base Camp

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 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 avail ...

monohydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...

() and to "blue verdigris" as . Other sources describe the main copper salt in natural verdigris as (

brochantite Brochantite is a sulfate mineral, one of a number of cupric sulfates. Its chemical formula is Cu4SO4(OH)6. Formed in arid climates or in rapidly oxidizing copper sulfide deposits, it was named by Armand Lévy for his fellow Frenchman, geologist ...

). Still other sources describe it as

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 wi ...

(),Sharp, D. W. A: ''Penguin Dictionary of Chemistry'', page 419. Penguin Books, 1990 (2nd edition) or as where ''n'' varies from 0 to 3. In marine environments, the main copper salt is tribasic copper chloride (). Overall, variations of verdigris can be divided into two groups: basic verdigris and neutral verdigris. The difference in colour depends on the hydration level and degrees of

Toxicity

Verdigris, which was once used as a medicine and pharmaceutical preparation Symptoms of toxicity include nausea, anemia and death, although widespread acquired immunity has been documented, as occurred with female workers in

. 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 be a desirable artistic effect, it has been used primarily as a pigment and now-outdated medicinal preparations.

Pigment

Verdigris has been used as a pigment since antiquity, including in paintings in Rome and Pompeii. The use of verdigris continued into the

Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass ideas ...

and

Baroque The Baroque (, ; ) is a style of architecture, music, dance, painting, sculpture, poetry, and other arts that flourished in Europe from the early 17th century until the 1750s. In the territories of the Spanish and Portuguese empires including t ...

paintings. It has been identified in ''The Last Supper'' (1306) by

Giotto Giotto di Bondone (; – January 8, 1337), known mononymously as Giotto ( , ) and Latinised as Giottus, was an Italian painter and architect from Florence during the Late Middle Ages. He worked during the Gothic/Proto-Renaissance period. Giot ...

. During the 15th and 16th centuries, it was used in paintings for its transparency and brilliance. It was difficult to create strong

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...

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 A landscape is the visible features of an area of Terrestrial ecoregion, land, its landforms, and how they integrate with Nature, natural or man-made features, often considered in terms of their aesthetic appeal.''New Oxford American Dictionar ...

and

drapery Drapery is a general word referring to cloths or textiles (Old French , from Late Latin ). It may refer to cloth used for decorative purposes – such as around windows – or to the trade of retailing cloth, originally mostly for clothin ...

, such as the green coat of Saint John in the ''

Mond Crucifixion The ''Mond Crucifixion'' or ''Gavari Altarpiece'' is an oil on poplar panel dated to 1502–1503, making it one of the earliest works by Italian Renaissance artist Raphael, perhaps the second after the c.1499-1500 Baronci Altarpiece. It origina ...

'' by

Raphael Raffaello Sanzio da Urbino, better known as Raphael (; or ; March 28 or April 6, 1483April 6, 1520), was an Italian painter and architect of the High Renaissance. List of works by Raphael, His work is admired for its clarity of form, ease of ...

. Verdigris was used as both glaze and opaque paint. When verdigris glaze was combined with

lead white White lead is the basic lead carbonate 2PbCO3·Pb(OH)2. It is a complex salt, containing both carbonate and hydroxide ions. White lead occurs naturally as a mineral, in which context it is known as hydrocerussite, a hydrate of cerussite. It was ...

or lead-tin yellow, it created a deeply saturated green. 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 Lacquer is a type of hard and usually shiny coating or finish applied to materials such as wood or metal. It is most often made from resin extracted from trees and waxes and has been in use since antiquity. Asian lacquerware, which may be ca ...

. However, during the 19th century, the use of verdigris began to decrease as alternatives such as

Emerald Green Varieties of the color green may differ in hue, chroma (also called saturation or intensity) or lightness (or value, tone, or brightness), or in two or three of these qualities. Variations in value are also called tints and shades, a tint b ...

and

viridian Viridian is a blue-green pigment, a hydrated chromium(III) oxide, of medium saturation and relatively dark in value. It is composed of a majority of green, followed by blue. Specifically, it is a shade of spring green, which places the color b ...

became more popular.

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 A binder or binding agent is any material or substance that holds or draws other materials together to form a cohesive whole mechanically, chemically, by adhesion or cohesion. In a more narrow sense, binders are liquid or dough-like substances th ...

and type of verdigris used. For example, changes are less pronounced with neutral verdigris in oil and

egg tempera Tempera (), also known as egg tempera, is a permanent, fast-drying painting medium consisting of colored pigments mixed with a water-soluble binder medium, usually glutinous material such as egg yolk. Tempera also refers to the paintings done ...

compared to basic verdigris. With aging, the green pigment in these applications will show signs of browning or darkening. For example, in

Botticelli Alessandro di Mariano di Vanni Filipepi ( – May 17, 1510), known as Sandro Botticelli (, ), was an Italian painter of the Early Renaissance. Botticelli's posthumous reputation suffered until the late 19th century, when he was rediscovered ...

's ''

The Mystical Nativity ''The Mystical Nativity'' is a painting in oil on canvas dated by the Italian Renaissance master Sandro Botticelli, in the National Gallery in London. It is his only signed work and has an unusual iconography for a painting of the Nativity. Th ...

'', from 1500, the blue-green costumes of the angels have darkened to a dark green colour. Verdigris pigment is

lightfast Lightfastness is a property of a colourant such as dye or pigment that describes its resistance to fading when exposed to light. Dyes and pigments are used for example for dyeing of fabrics, plastics or other materials and manufacturing paints or ...

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 natu ...

, is not lightfast, even in oil paint. In the presence of light and air, green copper resinate becomes stable brown copper oxide. 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 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 compo ...

. Furthermore, linseed oil induces the transformation of the copper acetate bimetallic structure, and forms

monomer In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification Mo ...

ic series.

Dioxygen There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are: *A ...

that reacts with partially

decarboxylated Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...

dimers to form a peroxy-Cu dimer complex is responsible for the darkening of the pigment. 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 Varnish is a clear transparent hard protective coating or film. It is not a stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, and is sold commercially in various ...

to avoid rapid discoloration (but not in the case of oil paint). 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. In terms of identification and reproduction, modern technology and reproducible synthesis procedures have been developed to be used for

museum A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make these ...

s and collections to identify distinct verdigris phases in historical artworks. Certain components of historical verdigris pigments,

s, are partially

irreproducible Reproducibility, also known as replicability and repeatability, is a major principle underpinning the scientific method. For the findings of a study to be reproducible means that results obtained by an experiment or an observational study or in a ...

based on the given historical recipes.

Medicine

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 succeeded ...

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 ...

. Verdigris solids were also used for pharmaceutical preparations in the 18th century to treat

canker sores A plant canker is a small area of dead tissue, which grows slowly, often over years. Some cankers are of only minor consequence, but others are ultimately lethal and therefore can have major economic implications for agriculture and horticultur ...

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