A mildly photosensitive solution composed of potassium ferricyanide and ferric ammonium citrate is applied to a receptive surface, such as paper, and allowed to dry in a dark place.
A positive image can be produced by exposing it to a source of ultraviolet light (such as sunlight) as a contact print through the negative. The combination of UV light and the citrate reduces the iron(III) to iron(II). This is followed by a complex reaction of the iron(II) complex with ferricyanide. The result is an insoluble, blue dye (ferric ferrocyanide) known as Prussian blue. The extent of colour change depends on the amount of UV light.
Cyanotype on Hahnemühle German Etching and Canson L'Aquarelle paper.
The Angels' rest
Artichokes
