Carbon Prints and Gum Bichromate Prints – The Pigment Processes – Invention of Photography 5.44 min video created by George Eastman House.
Carbon prints and gum bichromate prints are both examples of pigment processes. Rather than the metal salts typically used in the formation of photographic images, pigments and bichromated colloids are used in making these prints.
A bichromated colloid is a viscous substance such as gelatin or albumen that is made light-sensitive by the addition of a bichromate. Bichromated colloids harden when exposed to light and become insoluble in water; this is the principle behind many of the non-silver-based photographic processes.
Pigment processes were developed in the 1850s and offer superior permanence and control of the appearance of the final print. The resulting prints are characterized by broad tones and soft detail, sometimes resembling paintings or drawings.
(This video is made possible by a grant from the U.S. Institute of Museum and Library Services, grant number MA-10-13-0194.)
George Eastman House, an independent nonprofit museum, is an educational institution that tells the story of photography and motion pictures—media that have changed and continue to change our perception of the world.