Some people call this process “Sun Printing” but that’s a fairly simplified way to explain a complex process. Cyanotype process was one of the first non-silver technologies used to create photographic images.

The technique was invented in 1841 by astronomer and scientist Sir JohnHerschel, and was popularised by photographer and botanist Anna Atkins. Her book ‘Photographs of British Algae: Cyanotype Impressions’, published in October 1843, is considered the first photographically illustrated book.

Mainstream photography eventually adopted cyanotype as a copying technique and this became known as a “blueprint”. This blue, called Prussian Blue, was used in reproductions of large architectural and mechanical drawings.
To begin the process, two solutions are prepared for the two-part sensitizing process. Material sensitized with the solution is then printed by ultraviolet light.
Variations of the original formula involve different ratios of the following chemicals:(1) Potassium ferricyanide and (2) Ferric ammonium citrate(green). Too much potassium ferricyanide in the solution will lower printing speed; too little may cause the blue color to bleed into the lighter areas. Basically equal volumes of the two solutions are used.
Each print is an original and cannot be recreated. Process times vary depending on the amount of sunlight. I mix my own chemistry, although paper and fabric can be purchased that already have the cyanotype chemicals on them.

Caring for your cyanotype: HERE