Ochre - Pigment

Pigment

Ochres are non-toxic, and can be used to make an oil paint that dries quickly and covers surfaces thoroughly. To manufacture ground ochre, ochre clay is first mined from the ground. It is then washed in order to separate sand from ochre, which can be done by hand. The remaining ochre is then dried in the sun and sometimes burned to enhance the natural color.

As a painting pigment, it exists in at least four forms:

• Yellow ochre, Fe₂O₃ • H₂O, a hydrated iron oxide, also called Gold ochre
• Red ochre, Fe₂O₃, is the anhydrate of yellow ochre, which turns red when heated because heat drives off the water ligands
• 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 (Goethite), also partly hydrated iron oxide (rust)

They are found throughout the world in many shades. Many sources consider the best brown ochre to come from Cyprus, and the best yellow and red ochre from Roussillon, France. All have been used since prehistoric times.