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Calcination and transformation
After the various phases of extraction, washing, settling, and drying, the ocher is transported to the factory to complete its manufacture and undergo calcination. The iron oxide of raw ochres is a goethite (hydrated oxide) which, when heated to 1472-1652°F (800-900°C) in gas rotary ovens, dehydrates and turns into hematite. Its color, usually yellow, then becomes red. The ovens, usually 49.2 ft (15 m) in length and 3.2 ft (1 m) in diameter, are bricked to keep the heat.
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