The cyanotype or blue-print was one of the first photographic printing processes (in some early texts it is called the 'ferroprussiate process') and remains one of the simplest. Its main characteristic, as the name suggests is that it produces blue prints, usually a deep blue colour, although the lighter tones may be slightly more cyan. The colour varies slightly on different papers and with different methods of production, and occasionally cyanotypes were toned to give purplish or brown.
Cyanotypes are prints made on ordinary paper with a matte surface. Photographic images are contact printed from a negative, although a positive working cyanotype process was often used for the production of copies of large plans and engineering drawings (blueprints.) The term cyanotype is sometimes chosen to distinguish the negative image-making process from the technical positive working blue-print.
Under suitable storage conditions, cyanotypes have proven to be extremely stable.
