Cyanotype is a photographic printing process that produces a cyan-blue print. Engineers used the process well into the 20th century as a simple and low-cost process to produce copies of drawings, referred to as blueprints. The process uses two chemicals: ferric ammonium citrate and potassium ferricyanide. You can get the chemicals in a pack at your neighborhood art store.
The English scientist and astronomer Sir John Herschel discovered cyanotype in 1842. Though the process was developed by Herschel, he considered it as mainly a means of reproducing notes and diagrams, as in blueprints.
Anna Atkins created a series of cyanotype limited-edition books that documented ferns and other plant life from her extensive seaweed collection, placing specimens directly onto coated paper and allowing the action of light to create a silhouette effect. By using this photogram process, Anna Atkins is sometimes considered the first female photographer.
Cyanotype photography was popular in Victorian England, but became less popular as photography improved. Another proponent of the craft was Washington Teasdale from Leeds.
Numerous contemporary artists employ the cyanotype process in their art: Christian Marclay, Marco Breuer, Kate Cordsen and John Dugdale.