Copper dyes

Copper compounds produce a large amount of green or blue colored pigments. They can be natural or artificial.
N a t u r a l ones, such as azurite, malachite and mountain blue, were known in ancient times. They are carbon-copper compounds.
S t u c k s - are a mixture of copper compounds.

There are three main types of copper compounds yielding copper dyes:

1.Copper carbonates: mountain blue, Bremen green, Hamburg green, Brunswick green.
2.Copper acetates: gritschop, French green.
3.Arseno-acetates of copper (the most poisonous group): schweinfurtz green, Paola Veronese green.

Properties of the above groups:

1.More or less poisonous.
2.Intense color.
3.Sensitivity to sulfur compounds and combinations with sulfur dyes (blacken).
4.Ability to react with organic dyes.
5.Formation of chemical compounds with oil, so-called "copper soaps" (copper salts of fatty acids).
6.Blue copper dyes in oil turn green after some time.

Copper dyes are most useful in wall techniques.In easel painting they can be used with great care, avoiding combinations.
Malachite green is the most durable.
In general, copper ones are going out of use.