Pigments-copper-based greens and blues

Since antiquity, various copper-containing substances have been used as green and blue pigments. Their exceptional diversity, reflecting their various chemical and phase composition, chemical stability as well as their origin, makes their correct identification challenging. The review focuses on copper-based pigments used in ancient and mediaeval works of art, especially in wall paintings and/or related polychromed decorations or statues-siliceous copper pigments (Egyptian blue and green, Han blue and purple, chrysocolla), copper carbonates (azurite, malachite, blue and green verditers), copper chlorides (atacamite-group, cumengeite, calumetite), copper sulphates (posnjakite, brochantite) and-to a lesser extent-copper acetates (verdigris) and other organometallics. Particular attention is given to the necessity of the detailed study of accompanying phases which can serve as useful indicators of natural and/or artificial origin of copper pigments. Factors affecting the stability of copper pigments in wall paintings-salt attack, oxalic acid, alkalinity and heat-are overviewed. A suitable analytical approach based on complemental combination of in situ and laboratory analyses for proper identification and differentiation of copper pigments is proposed.

Automated summary

This review discusses the diverse copper-based pigments used in ancient and mediaeval artworks, such as siliceous copper pigments, copper carbonates, copper chlorides, and copper sulphates. It also highlights factors affecting the stability of these pigments in wall paintings and proposes a suitable analytical approach for their proper identification.