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Potassium ferricyanide

Potassium ferricyanide (K3Fe(CN)6), also known as Red prussiate or Prussian Red, is a coordination compound that is stable at room temperature and pressure and forms ruby red crystals and powder. It is manufactured by passing chlorine gas through solutions of potassium ferrocyanide. Potassium ferricyanide then separates out of the solution.

The compound has widespread use in blueprints and in photography. Iron and copper toning involve the use of potassium ferricyanide. Potassium ferricyanide is used as a reducing agent to remove silver from negatives and positives, a process called dot etching. In color photography, potassium ferricyanide is used to reduce the size of color dots without reducing their number, as a kind of manual color correction. The compound is also used to temper iron and steel, in electroplating, dyeing wool, as a laboratory reagent, and as a mild oxidizing agent in organic chemistry.

See also: potassium ferrocyanide, Prussian blue