What is Sunprint/ Cyanotype?
Sunprints are produced through cyanotype process. The word ‘cyan’ comes from Greek, meaning “dark blue substance”. Sunprints as the name implies, are photographic prints that produce distinctive dark blue when exposed to sunlight.
History of Cyanotype
The process was invented by Sir John Herschel, a brilliant astronomer and scientist, in 1842. FUN FACT: His father was the astronomer Sir William Herschel, who discovered the planet Uranus. Interestingly, Uranus, due to mostly methane gas in its atmosphere, appears cyan blue.
However, Herschel did not use cyanotype for photography, but for reproducing notes. It was a family friend, the botanist Anna Atkins, who used the cyanotype printing process in 1843 to create an album of algae specimens. She created the images by placing objects directly on photosensitive paper (Note: this process is also called a photogram). She is regarded as the first female photographer.
FUN FACT: The cyanotype process was also used to create copies of technical and architectural plans, and these copies were called blueprints; even though the cyanotype process is no longer used, any construction documents or detailed plan is still referred to as a blueprint.
What makes it blue?
The distinctive blue is created when iron salt solutions (rather than the silver salt solution of black and white photography) is exposed to the sun. These iron salt solutions are Potassium Ferricyanide and Ferric Ammonium Citrate. Combined and exposed to UV light, it creates Ferric Ferrocyanide, also known as Prussian Blue (named for the color of the Prussian military uniforms.)