ultramarine, blue pigment used chiefly as a coloring material and as a bluing agent. A double silicate of sodium and aluminum with some sulfur, it is prepared commercially from kaolin, sulfur, soda ash, and other inexpensive ingredients. It was formerly produced by grinding the rare mineral lapis lazuli and was very costly.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.