Verdigris (/ˈvɜːrdɪɡriː(s)/)[1] is a common name for any of a variety of somewhat toxic[2][3][4] copper salts of acetic acid, which range in colour from green to a bluish-green depending on their chemical composition.

[5]: 132  Once used as a medicine[6][7] and pharmaceutical preparation,[8]: 176 [9] 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.

[8]: 171  The instability of its appearance stems from its hydration level and basicity, which change as the pigment interacts with other materials over time.

[15] The historical methods used for producing verdigris have been recorded in artistic treaties, manuscripts on alchemy, works in natural history, and texts on medicine.

[16] Another method of production was developed in 18th-century Montpellier, France, a locale which had the ideal climate to produce verdigris for pulverization.

[8]: 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.

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.

[clarify][2][3][4][better source needed] Symptoms of toxicity include nausea, anemia and death, although widespread acquired immunity has been documented, as occurred with female workers in Montpellier.

When verdigris glaze was combined with lead white or lead-tin yellow, it created a deeply saturated green.

[11]: 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.

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

[5]: 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.

[23]: 14847 Verdigris has also been used in medicine,[6][7] and is identified in the Pharmacologia of John Ayrton Paris as the healing rust of the Spear of Telephus mentioned by Homer.