Cyanotypes are made by the application of a light-sensitive solution to a porous substrate followed by exposure to a UV light source such as the sun. They are characteristically blue, but can be toned to shades of brown. The process was invented by Sir John Herschel in 1842 and used by Anna Atkins in 1843 for the first ever book of photographs, Photographs of British Algae: Cyanotype Impressions in 1843. It is a form of contact printing, so the resulting print is the same size as the negative. I have used it for photograms, cliche verre and prints of my pinhole photos.