#64203
Red Prussiate of Potash

Ruby-red to orange-red crystals that are readily soluble in water. The salt is used in chemistry classes for growing red monoclinic crystals. The chemical industry requires red blood liquor salt as a weak oxidizing agent in organic syntheses. It is used in the production of Berlin blue and is required in vat dyeing. In analog photography, it is used as an attenuator during development. If an image is overexposed, the precipitated silver can be re-oxidized with the red blood liquor salt. In the past, it was used in cyanotype together with ammonium iron citrate or with ammonium iron oxalate. In this photographic cyanotype process, a light-sensitive layer is formed when solutions of the two substances are mixed. When light strikes it, Berlin blue is formed. The image is developed by rinsing with water. The soluble iron(II) salts are washed out, while the insoluble iron(III) salts remain in the paper and give the cyanotype its characteristic coloration.