PB30
Azurite is a naturally occuring copper carbonate, with a long history within European and Asian painting. It was mined in northern Europe, so was a less expensive source of blue than Lapis Lazuli, which was imported from Afghanistan. Medieval artists would often use Azurite in underpaintings, before applying layers of Lapis Lazuli during later stages of production.
It is best used in aqueous media, as the acidity of oils can cause it to darken in colour, although this can be somewhat counteracted by protecting the pigment particles with a protein such as egg yolk. It has a very low tinting strength, and the particle size tends to be quite large, to give a darker colour. It is sensitive to damp conditions, and is slightly transparent.