ochers

Ochres are natural clay-based pigments composed primarily of hydrated iron oxide minerals. They occur in earthy tones ranging from pale yellows to deep reds and browns. The principal component is iron oxide hydroxide, typically FeO(OH)·nH2O, with color determined by oxidation state, hydration level, and impurities. Yellow ochre contains goethite; red ochre is richer in hematite; brown and burnt ochre result from dehydration and varying mineral content.

Processing and varieties: Ochre is usually mined and ground to a fine powder. It may be purified or mixed with other minerals to adjust color and texture. Heating ochre (burning) removes water and shifts the color toward red or brown, producing burnt ochre. The color range can be classified broadly as yellow ochre, golden ochre, red ochre, and brown ochre, with natural impurities contributing subtle variations.

Uses and history: Ochres have been used as pigments since prehistoric times, evident in cave paintings and ancient pottery decoration. They remain common in traditional and contemporary painting, ceramics, cosmetics, and art restoration due to their astringent lightfastness and natural composition. Synthetic iron oxide pigments, including synthetic ochres, are also produced for precise color control and consistency.

Geography and production context: Large natural deposits are found in several regions, including parts of France, Spain, Italy, and various locations in Africa and Australia. Today, ochre is produced both as natural pigment and as synthetic iron oxide pigments, serving artistic, industrial, and cosmetic markets.

Safety: Fine ochre powders can irritate the respiratory tract if inhaled; appropriate handling and ventilation are advised.