Prussianblue

Prussian blue, also known as Berlin blue, is a dark blue pigment widely used in art, printing, and various industrial applications. It is chemically described as iron(III) hexacyanoferrate(II), with the approximate formula Fe4[Fe(CN)6]3·xH2O. The compound is a mixed-valence iron complex that yields a deep, intense blue color and is typically insoluble in water.

The pigment was discovered in 1704 by Johann Jacob Diesbach in Berlin, apparently during a failed attempt to produce a red pigment. Its emergence in Prussia led to the common name Prussian blue. It quickly became one of the most important blue pigments of the 18th and 19th centuries and influenced the development of several blue hues and printing processes.

Production and properties are based on reacting iron salts with potassium ferrocyanide under alkaline conditions to form the insoluble blue precipitate. The pigment is known for its stability and lightfastness, resisting many forms of deterioration better than organic blue dyes. It is widely used in oil, tempera, and watercolor painting, as well as in dyeing and in the blue-printing process (cyanotype) due to its vivid coloration and durability.

Prussian blue has additional medical significance. In modern medicine, radiopharmacological formulations use ferric hexacyanoferrate to act as an intestinal adsorbent. Under the brand name Radiogardase, it binds cesium-137 and thallium in the gastrointestinal tract to reduce systemic absorption following exposure.

Prussian blue remains a foundational component in pigment history and has found enduring relevance in both art and applied science.