Azurite is a copper based blue pigment popular from Roman times until replaced by synthetic ultramarine and cobalt blue in the 19th century. Although natural Ultramarine was preferred, the low cost and ready availability of Azurite made it an important blue. Better as a water based color, it never performed as well when bound in oil, and soon died out after the discoveries of affordable cobalt and ultramarine in the 1820’s. Due to its natural occurrence with the green malachite, this impurity often made it a beautiful sky blue color. Often the ethereal blue of the sky in some renaissance landscapes is pure Azurite.