Potassium ferrocyanide is the inorganic compound with formula K4[Fe(CN)6]·3H2O. It is the potassium salt of the coordination complex [Fe(CN)6]4−. This salt forms lemon-yellow monoclinic crystals.
Potassium ferrocyanide
Prussian blue is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula FeIII4[FeII(CN)6]3. Turnbull's blue is chemically identical, but is made from different reagents, and its slightly different color stems from different impurities and particle sizes.
Prussian blue
The Great Wave off Kanagawa by Hokusai, an artwork that makes extensive use of Prussian blue
Prussian blue in a vial
Simulated powder x-ray diffraction profile for Prussian blue crystal, crystallographic direction annotated. Image generated using CrystalMaker software.