Ochre, earthy oxide of iron employed with oil as a paint. When obtained as a native product it is intermixed with argillaceous or calcareous earth; and it is also prepared by the decomposition and oxidation of pyritous ores. Deposits of it are produced about springs that flow from rocky beds which contain decomposed iron pyrites. The color of the material varies with the degree of oxidation of the iron, and may be changed by heat from yellow to brown and red. The earthy matters present also affect its color, and these may be partially or wholly removed by washing, the heavy sediments remaining behind. For the finer varieties of ochre these sediments are ground in mills. Ochres are sold under a variety of names. The coarser sorts are sometimes known as stone ochres. A kind from the Persian gulf is called Indian red. There are also the Spanish brown, a yellow variety known as the French ochre, the Oxford and Roman ochres of brownish yellow colors, and others distinguished merely by the names of their colors.

Dr. Thomson says the term ochre is applied to native oxides of cerium, molybdenum, lead, tungsten, chromium, and uranium.