Ochre

Argillaceous earth of different colours which, when finely ground, is used as a pigment. Red ochre is a form of specular iron ore; brown ochre is a variety of hæmatite. The yellow ochres become red when calcined, but the finest reds are made from those which are brown in the bed. Native red ochre is called red chalk or reddle in England. Spanish Brown, Indian Red, Venetian Red, and the yellow ochres have nearly the same composition. The other ochres are known as Oxford, Roman, and stone ochres, and as terra di Sienna and umber. They are all valuable and durable pigments for oil, water, or enamel painting. (See Am at it a.)