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Verdigris [44450]

Verdigris [44450]

Verdigris [44450]

 

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Product details

synthetic, coarse bluish green powder, contains copper. PG 20.77408

CI: PG 20

Chemical Formula: Cu(CH3COO)2·[Cu(OH)2]3·2H2O

Suitability: Oil, Acrylics, Tempera, Watercolor / Gouache

44450 Verdigris PG 20

Chemical composition : Cu(CH3COO)2·[Cu(OH)2]3·2H2O

Verdigris is basic copper acetate, but sometimes the term is falsely also used to indicate copper carbonate or any other blue or green corrosion product of copper, brass or bronze. Verdigris is a bluish green crystalline powder with an acetic odor.

The preparation of verdigris was known in ancient times and recipes can be found in numerous manuscipts. It is mentioned in Greek and Roman literature, where the termaerugo refers to various blue-green and green corrosion products formed ar the surface of copper, copper alloy and copper ores. Current usage of the term verdigris refers exclusively to the copper salts of acetic acid and probably derived from vert de Grèce mentioned in ancient texts.

Verdigris was prepared by exposing copper to the vapors of fermenting grape skins or in closed casks over vinegar. The action of acetic vapors on metallic copper produced basic or "crude" verdirgris, which can be lixivated and the product recrystallized from acetic acid. This product known as neutral verdigris and can also be used as a pigment or to make copper resinate.

Well crystallized verdigris particles have the shape of pointed needles. They often unite in bundles, while the larger pieces show fibrous structure.

In earlier centuries, literature on painting warned against the instabilty of verdigris, its use would lead to deterioration of other pigments and it could only be used under special conditions which should be strictly followed. However, observation on paintings and experiments with paint specimens show that verdigris does not manifest any harmful alterations to the paint quality or stability. Many areas containing verdigris found in old paintings contain additions of lead white and/or lead-tin yellow. A mixture of verdigris with orpiment (yellow arsenic sulfide) bound in an oil-medium has remained unchanged. Mixtures of verdigris with sulfur-containing pigments (such as ultramarine blue) in aqueous media may darken due to the formation of copper sulfide. Verdigris, in common with other copper containing pigments, will degrade paper and other cellulosic materials.

Experiments with prepared paint specimens have shown that verdigris paints in both aqueous- as well as oil-mediums have good lightfastness.


excerpts from:
Artist's Pigments Vol.2 Ashok Roy (editor) and
Painting Materials Rutherford J. Gettens and George L. Stout

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