Fe4[Fe(CN)6]3 - A vivid, lightfast blue pigment. Prussian blue, synthetically produced ferric ferrocyanide, was developed in Berlin in 1704 by Diesbach. It is made by adding ferric chloride to a boiling solution of hexacyano ferrate. This forms a white intermediate, called Berlin white, that is oxidised in air to produce Prussian blue. Prussian blue has deep blue, finely divided particles that are transparent in watercolours. It has high tinting strength and is stable to light, although it will fade in strong light and turns brown in the presence of alkalis or heat. It is therefore inappropriate to use it on plaster walls. Prussian blue was the first cheap and stable pigment to replace the costly minerals azurite and lapis lazuli. It has tremendous tinting strength and is used as a pigment in watercolour and oil paints. It is listed among the pigments used for colouring stucco marble in the nineteenth and twentieth century. Synonyms: ferric ferrocyanide; iron blue; Turnbull's blue; Paris blue; Milori blue; Chinese blue; bronze blue; Berlin blue; American blue; Antwerp blue; steel blue; mineral blue; Hamburg blue; Pigment Blue 27; CI 77510; toning blue; gas blue; new blue; Erlanger blue; celestial blue; lacquer blue; soluble blue; oriental blue; Persian blue; potash blue; paste blue; Preussisch Blau (Ger.); bleu de Prusse (Fr,); Berlinerblau (Ger.); azzurro di Prussia (It.); azul de Prusia (Sp.); konjo (Jap.); yang lan (Ch.). Wittenburg (1999); Trench (2000); Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]