Cyanotype is a photographic printing process that produces a cyan-blue print. Engineers used the process well into the 20th century as a simple and low-cost process to produce copies of drawings, referred to as blueprints. The process uses two chemicals: ferric ammonium citrate and potassium ferricyanide.
Potassium ferricyanide is the chemical compound with the formula K3[Fe(CN)6]. It is soluble in water and its solution shows some green-yellow fluorescence.
The compound has widespread use in blueprint drawing and in photography (Cyanotype process). Several photographic print toning processes involve the use of potassium ferricyanide.
Potassium ferricyanide has low toxicity, its main hazard being that it is a mild irritant to the eyes and skin.
