Cyanotype is an old monochrome photographic printing process which creates a cyan-blue print. English scientist and astronomer Sir John Herschel discovered it in 1842. Though Sir John Herschel is perhaps the inventor of the procedure, it was Anna Atkins, a British scientist, who brought the process to photography. She created a limited series of cyanotype books that documented ferns and other plant life. By using this process, Anna Atkins is regarded as the first woman photographer.
The developing of the picture takes place by flushing it with flowing water. The water-soluble Iron(II) salts are washed away, while the non-water-soluble Prussian Blue remain in the paper. This is what gives the picture its typical blue color. The process was popular in engineering circles well into the 20th century. The simple and low-cost process enabled them to produce large-scale copies of their work, referred to as “blueprints”.