Invented by Sir John Herschel in 1842, the cyanotype process requires Potassium ferricyanide and Ferric ammonium citrate to be mixed with water. The two solutions are then blended together in equal parts. Any naturally absorbent material (paper or textile) is coated with the solution and dried in the dark. Objects or negatives are placed on the material to make a print. The cyanotype is printed using UV light, such as the sun, a light box or a UV lamp. After exposure the material is processed by simply rinsing it in water, producing a white print on a blue background.