Description

Ferric ammonium ferrocyanide is a synthetic colorant used to impart a blue color to cosmetic formulas, paint, and printer ink. It is closely related to ferric ferrocyanide, or Prussian Blue, but is not the same chemical. It belongs to a class of chemicals called inorganic cyanides. It has long-standing approval as a colorant in foods and cosmetics by the FDA and in the EU. It's made by reacting sodium dichromate in acid, then reacting with ferrous sulfate and sodium ferrocyanide in the presence of ammonium sulfate. The oxidized product is filtered, washed, and dried. The pigment consists principally of ferric ammonium ferrocyanide with smaller amounts of ferric ferrocyanide and ferric sodium ferrocyanide.