Cyanotype is one of the oldest monochrome processes that do not use silver salts.
It is based on the reaction of iron salts to light, and it is a relatively quick, simple, and low-cost approach. A solution of ammonium iron citrate and potassium ferricyanide is applied onto the paper, which is then allowed to dry in a dark place. The print is exposed by contact under the negative. About fifteen minutes of exposure to natural light changes the composition of the iron salts. The paper is then rinsed with water to dissolve the unexposed iron salts, and dried. The characteristic Prussian blue pigment is formed during the drying process.
Although invented in 1842 by English scientist John Frederick Herschel, the process did not achieve success until later: its deep, intense blue and pictorial results did not appeal to photographers at the time, who were seeking a more realistic look. It was used at first for essentially documentary purposes, such as copy making, architectural plans, and industrial drawings. In the 1940s-50s, however, it did draw the attention of two main photographers: the English botanist Anna Atkins, who used it to produce photograms of dried plants, and the French artist Henri Le Secq, for his work on the gothic monuments of Paris and his still lifes. The process finally became popular in the late 19th century. It was valued by the pictorialists, particularly Paul Burty Haviland, who were keenly interested in its aesthetic qualities.
Today, cyanotype is used by many contemporary artists among whom Nancy Wilson Pajic or Christian Marclay.
Visual glossary of photographic techniques
© ARCP / Mairie de Paris, 2013