Potassium Ferricyanide - Prussian Blue

Prussian Blue

Prussian blue, the deep blue pigment in blue printing, is generated by the reaction of K₃ with ferrous (Fe2+) ions.

In histology, potassium ferricyanide is used to detect ferrous iron in biological tissue, as the stain Perls' Prussian blue. In this reaction, potassium ferricyanide reacts with ferrous iron in acidic solution to produce an insoluble blue pigment, and both the stain and the pigment are commonly referred to as Turnbull's blue. To detect ferric (Fe3+) iron, potassium ferrocyanide is used instead; the stain and pigment produced are commonly known as Prussian blue. It has been found that the compound formed in the Turnbull's blue reaction and the compound formed in the Prussian blue reaction are the same unique compound, Prussian blue.