Ochre is a family of earth pigments, which includes yellow ochre, red ochre, purple ochre, sienna, and umber. The major ingredient of all the ochres is iron(III) oxide-hydroxide, known as limonite, which gives them a yellow colour. Yellow ochre (Goldochre)- pigment Yellow ochre, FeO(OH)·nH 2O, is a hydrated iron hydroxide (limonite) also called gold ochre. Red ochre, Fe 2O 3, takes its reddish colour from the mineral hematite, which is an anhydrous iron oxide. Purple ochre is identical to red ochre chemically but of a different hue caused by different light diffraction properties associated with a greater average particle size. Brown ochre, also FeO(OH), (goethite), is a partly hydrated iron oxide. Sienna contains both limonite and a small amount of manganese oxide (less than five percent), which makes it darker than ochre.
