Ochres

Ochres are native pigments consisting of clays or earths composed chiefly of silica and alumina, along with oxide of iron or more rarely with other oxides. Some are found in a natural state fine enough to be used after being simply washed. The two important classes of ochres are the yellow and the red, the colouring material of the former being the hydrated oxide of iron, and that of the latter the red or sesquioxide. Umber (q.v.), which is classed with the ochres, contains manganese as well as oxide of iron. Yellow ochres are reddened by being burned. Most of the ochres can be prepared artificially, but these are not so safe for artists' purposes as the native earths. The latter are remarkable for their stability, as can be seen in many pictures by the old masters. Yellow ochre and Roman ochre are much used both by artists and house-painters, and so also (but the first more by artists) are the red ochres, known as light red, Indian red, and Venetian red. This last, however, is an artificial product, and, although it is an oxide of iron colour, it contains no earthy base, so that correctly speaking it is not an ochre. Ochre is found in several English counties, but it is most largely worked in Anglesey and Devonshire. About 12,000 tons are raised in some years, the value of which is roundly £2 per ton. It occurs in many other countries, there being large deposits of it in Canada. The earthy or powdery varieties of some of the less common metallic compounds found native are called ochres by mineralogists. Among these there are bismuth ochre, antimony ochre, nickel ochre, and chrome ochre.