Verdigris

Verdigris is a basic acetate of copper, or rather it is a mixture of three such acetates. This substance has long been largely made at Montpellier in France, by exposing thin sheets or strips of copper to the vapour of acetic acid arising from fermenting grape skins. Verdigris is used by itself as a green pigment, and also in the manufacture of several other green colours. It was in use as a paint by the ancient Romans, and it has continued to be employed as such to the present time. But as it suffers from exposure to impure air, and acts injuriously on some other pigments if mixed with them, it has fallen very much out of use for artistic work. Mixed with white-lead, it is largely used in Russia for painting iron roofs, the mixed paint changing by exposure from a bluish to a fine green colour. External wood-work is coated with it in Holland, partly, perhaps, because it is a good preservative of timber. It is mixed with some dark colours as a 'drier,' and is employed as an external application in surgery. Verdigris is very poisonous, and as it has a tendency to form on copper cooking-vessels they should always be kept perfectly clean.