Cyanotype is a photographic printing process that produces a distinctive blue image. It involves mixing two chemicals, ferric ammonium citrate and potassium ferricyanide, which react to ultraviolet light. When a surface coated with this mixture is exposed to sunlight, areas not covered by an object or negative turn blue, creating a striking contrast. This technique was invented in 1842 by Sir John Herschel, a British scientist. Cyanotype is often used for artistic purposes, such as creating photograms or prints of plants, due to its simplicity and the vibrant blue color it produces.