A variety of inorganic color pigments used in printing inks, derived from a complex iron compound, generally potassium ferric ferrocynanide—chemical formula KFe(Fe[CN]6) x H2O—although the potassium may be replaced by sodium, ammonium, or some combination of both. Iron Blues range from highly transparent (some of the lighter shades) to highly opaque (the darker shades). Iron Blues possess high lightfastness and resistance to acids, oils, waxes, and heat, but react strongly to alkalis. They are also prone to spontaneous combustion if the undispersed pigment particles are left unmilled. They are highly popular pigments, however, primarily due to their low cost and high strength. Tinted Iron Blues can degrade upon storage, turning green and dirty. Various shades of Iron Blue include Chinese Blue, Milori Blue (or Bronze Blue), Prussian Blue, and Toning Blue). (See Inorganic Color Pigments.)
('CI Pigment Blue 27 No. 77510'.)