Ironblue

Ironblue, commonly known as Prussian blue, is a dark blue pigment that has played a major role in painting, printing, and dyeing since the early 18th century. It is chemically ferric ferrocyanide, Fe4[Fe(CN)6]3, often expressed as Fe4[Fe(CN)6]3·xH2O, and forms when iron salts react with ferrocyanide under alkaline conditions.

Discovery and naming: The pigment was discovered in 1704 in Berlin by Johann Jacob Diesbach, who was attempting to produce a red pigment and instead created a vivid blue. It was marketed as Berlin blue or Paris blue, and the name Prussian blue became common in many languages.

Chemical properties and production: Prussian blue is a coordination polymer with iron in mixed valence states. Its color depends on particle size and medium. It is valued for strong tinting strength and relatively high colorfastness in oil and watercolor media.

Applications: In art, it became a standard pigment for painters from the 18th century onward. It also found use in blueprints and cyanotype photographic processes due to its deep blue color. In printing and textiles, it served as a stable dye and pigment.

Medical use: The compound ferric ferrocyanide is used clinically as an antidote for certain types of heavy metal poisoning, particularly radioactive cesium and thallium, in a drug called Prussian blue.

Modern status: Although newer blues have broadened the palette, Prussian blue remains in use for artistic, archival, and medical applications, and its historical importance is recognized in art history and industrial chemistry.