Cyanotype (sa-YAN-no-type) is a photographic printing process invented in 1842 by Sir John Herschel, and is one of the oldest printing processes in the history of photography. Its telltale characteristic is the Prussian blue color—a result of a chemical reaction when cyanotype chemicals are exposed to ultraviolet light. English botanist Anna Atkins used the cyanotype process to create Photographs of British Algae: Cyanotype Impressions in 1843, marking the first book illustrated with photographs.
