Chessylite

Synonyms:

Chessylite, Blue Verditer, Bice, Mountain Blue, Azurite, Cendres Bleues, Bergblau

Azurite. Ref.: Wikimedia Commons, User "Noodle_snacks"

This copper mineral differs from malachite in containing less hydrate, or more carbonate of the metal, its composition being represented by the formula Cu₃(CO₃)₂(OH)₂. Its best-known locality is Chessy, near Lyon, in France, but very fine specimens are found at Wallaroo and Burra-Burra, in South Australia, and in the district of Perm, Siberia.

This blue pigment has been prepared artificially, but the natural substance is far less liable to change on exposure to impure air. The introduction of cobalt blue, and more particularly of artificial ultramarine, has practically caused the disuse of blue verditer, or rather of chessylite (= azurite), this beautiful native blue pigment, which, when used in illuminated manuscripts, as was largely the case between the thirteenth and sixteenth centuries, has kept its hue unimpaired to the present day.

Under the name of Bleu Lumière a beautiful turquoise-coloured paint was introduced to artists. It consists mainly of an artificial copper hydrate along with some carbonate. It becomes greenish by exposure to sunlight or a very moderate degree of heat. Like all similar artificial compounds of copper it proves to be untrustworthy.

Many old pictures, especially those in tempera, afford evidence of the blue hydrato-carbonates of copper having become green. With the extensive range of more permanent blues at the command of the modern artist, there is no need to retain this pigment on the palette.