Prussian Blue
Composition and Properties of Prussian Blue
Prussian blue is an inorganic complex salt containing two differently charged iron ions Fe2+ and Fe3+ and the negatively charged hexacyanoferrate ions [Fe(CN)6]4–. The overall formula is usually written as Fe4[Fe(CN)6]3· x H2O. There are also variants containing other positive ions such as potassium K+ or sodium Na+.The pigment is decomposed by dilute alkalis to form brown iron hydroxide, but it is resistant against dilute mineral acids and withstands temperatures up to 140 °C. It is compatible with many pigments that are not alkaline, so it should not be mixed with lead white and calcium carbonate. The reports on the stability of this pigment vary and its lightfastness depends on several factors. In pure form, it is a permanent pigment but its lightfastness diminishes when mixed with other pigments.It is compatible with many pigments that are not alkaline, so it should not be mixed with lead white and calcium carbonate.
Names
Milori blue, iron blue, Turnbull’s bluePB 27, CI 77510From Prussia, the country in northern Germany
Preparation of Prussian Blue
The pigment can be prepared by a reaction of ferric chloride FeCl3 with potassium ferrocyanide K4[Fe(CN)6] in solution.
History of Use
It is the oldest modern synthetic pigment that has been in use since its discovery in 1704 until the present day. The following graph gives the frequency of its use in the paintings of the Schack Collection in the Bavarian State Art Collections in Munich (1).Examples of use
