Collotype

Collotype is a dichromate-based photographic process invented by Alphonse Poitevin in 1856 and used for large volume mechanical printing before the existence of cheaper offset lithography. It can produce results difficult to distinguish from metal-based photographic prints because of its microscopically fine reticulations which comprise the image. Many old postcards are collotypes. Its possibilities for fine art photography were first employed in the United States by Alfred Stieglitz.