All the industrially important production processes for (Ⅲ) oxide pigments start from chromates or dichromates, which are obtained by alkaline oxidative
digestion of chrome ores.

Manufacturing Processes in Aqueous Media

Chromium hydroxide or chromium oxide hydrate are formed when chromates are used as oxidizing agents in organic chemistry. These can be calcined to α-Cr₂O₃ or directly used as a pigment. Such processes have declined in importance, due to the increasing use of catalytic oxidation in organic chemistry.

Organic waste products such as molasses or sawdust and sulfur are particularly cheap reducing agents for chromates or dichromates. Polysulfide-containing sulfur suspensions are the most widely used reducing agents producing chromium hydroxide which is difficult to filter together with thiosulfate, which can be used for reducing further chromate. This is achieved by mixing the thiosulfate-containing suspension with additional in a kneader. The resulting granulate is then calcined to α-chromium(Ⅲ) oxide at 900 to 1100°C.

Manufacturing Processes in the Solid State

Sodium dichromate is reduced with sulfur by intensively mixing the components and then calcining in rotary kilns or rotary-plate furnaces at 800 to 1000°C.

The calcination product, which contains sodium sulfate in addition to chromium oxide and also possibly unreacted chromate, is purified by mashing with water, filtering and washing.
The presence of fluxes such as NaCl or Na₂SO₄ during the decomposition of ammonium dichromate ensures that Cr₂O₃-pigments are formed in addition to nitrogen and water, instead of extremely fine powders. The isolation of ammonium dichromate can therefore be dispensed with by calcining mixtures of sodium dichromate and ammonium chloride or ammonium sulfate at 800 to 1000 °C.

To ensure a good yield and high quality pigments, it is important that the intermediate formation of ammonium dichromate be as complete as possible.

The use of stoichiometric quantities of ammonium chloride or slightly under stoichiometric quantities of ammonium sulfate in the reaction mixture yields low sulfur chromium(Ⅲ) oxide for the manufacture of chromium metal.

The Cr₂O₃-pigments produced by the different processes are further processed by washing, filtering, drying and grinding.