Potassium ferricyanide is the chemical compound with the formula K3[Fe(CN)6]. This bright red salt contains the octahedrally coordinated [Fe(CN)6] ion. It is soluble in water and its solution shows some green-yellow fluorescence. It was discovered in 1822 by Leopold Gmelin.
The cyanotype (from Ancient Greek: κυάνεος, kyáneos 'dark blue' and τύπος, týpos 'mark, impression, type') is a slow-reacting, photographic printing formulation sensitive to a limited near-ultraviolet and blue light spectrum, the range of 300 nm to 400 nm, known as UVA radiation. It produces a monochrome, blue-coloured print on a range of supports, and is often used for art and reprography in the form of blueprints. For any purpose, the process usually uses two chemicals – ferric ammonium citrate or ferric ammonium oxalate, and potassium ferricyanide, and only water to develop and fix. Announced in 1842, it is still in use.