Cyanotype

= a 19th-century camera-less photographic printing process, invented in 1842 by Sir John Herschel, that produces distinctive, monochrome Prussian blue images, often used in art to create ethereal silhouettes, photograms, and blueprints, which uses UV light (sunlight) to develop light-sensitive iron salts on paper or fabric, resulting in a permanent, cyan-blue print.