Cyanotype is a photographic printing process based on light-sensitive iron salts.

When a 50/50 mixture of Potassium Ferricyanide, and Ferric Ammonium Citrate are exposed to ultraviolet (UV) light, the ferric ions are reduced to ferrous ions, which react to form insoluble ferric ferrocyanide (Prussian blue pigment).

Areas blocked from light remain water soluble and wash away during rinsing, leaving a deep blue and white image.

The intensity of the blue depends on UV source, exposure time and chemical concentration, making cyanotype just as much an experiment as an art.