Iron oxide pigments

Iron oxide materials yield pigments that are nontoxic, nonbleeding, weather resistant, and lightfast. Natural iron oxides include a combination of one or more ferrous or ferric oxides, and impurities, such as manganese, clay, or organics. Synthetic iron oxides can be produced in various ways, including thermal decomposition of iron salts, such as ferrous sulfate, to produce reds; precipitation to produce yellows, reds, browns, and blacks (e.g., the Penniman-Zoph process); and reduction of organic compounds by iron (e.g., nitrobenzene reduced to aniline in the presence of particular chemicals) to produce yellows and blacks. Reds can be produced by calcining either yellow or blacks.

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• USGS Mineral Commodity Specialist