Brown ochre
Composition and Properties of Brown Ochre
The main color giving component of natural brown ochre (ocher) is limonite which is not a single mineral but a mixture of several iron-containing minerals among them goethite, akageneite, lepidocrocite, and jarosite, goethite (iron oxide hydroxide α-FeOOH) being the main component. The brown color may be at least partly caused by small amounts of manganese.Iron oxides can withstand high temperatures but are not resistant to acids. The pigment is absolutely stable as is documented by the cave paintings still in excellent condition after many thousands of years. It is compatible with all other pigments and is often used in mixture with other pigments.
Names
Brown ocherbrown earthPBr 7, CI 77492From Old French ocre (c. 1300) and directly from Medieval Latin ocra, from Latin ochra, from Greek khra, from khros “pale yellow,” a word of unknown origin. From Online Etymology Dictionary
Preparation
The natural mineral is washed in order to separate it from sand and other impurities. The resulting sludge is dried and the pigment is ground and sieved.Deposit of natural ochre in Rustrel, Provence, FranceBrown ochres can also be prepared artificially by a variety of procedures. There are two main types of production methods: precipitation of iron oxides and/or hydroxides from solutions of iron salts is one possibility (2,3), thermal decomposition of iron compounds the other.
History of Use
Natural ochre pigments have been in use since prehistoric times.Examples of use
