Several types of inorganic color pigments used in printing inks. Brown iron oxide pigments (in nearly all cases, chemical formula Fe2O3) are derived from natural or synthetic sources, and are classified as either brown pigments ('CI Pigment Brown 6 and 7 No. 77491 [77492] [77499] [synthetic or natural brown iron oxide, burnt sienna]) or red pigments ('CI Pigment Red 101 and 102 No. 77491 [synthetic or natural red iron oxides, red hematite]). They possess very high lightfastness and are resistant to all substances. The natural iron oxides are more difficult to process than the synthetic iron oxides, and are used less frequently. (See also Inorganic Color Pigments.)
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