gum bichromate

Gum Bichromate is an early 19th Century printing contact process that requires an emulsion made up of gum arabic (colloid), top quality watercolour pigments and Ammonium dichromate (the light sensitive component).

Watercolour paper is coated with the emulsion, dried and placed in contact with a large negative, exposed to a good UV light source and developed out in water and manipulated with soft brushes. The dichromated colloid hardens in proportion to the amount of exposure to UV light. The image is made up of several coats to increase the density.

The Gum Bichromate process was closely associated with the Pictorialist movement in photography, in which photographers placed less emphasis on achieving sharp-focused clarity and more on 'artistic' modification of the image. The main photographers using gum were Steiglitz in Europe, Steichen in America and Demachy and Maskell in England.

A great variety of subjects can be approached through gum, the essential is that the photographer wishes not merely to depict a subject but also to convey a mood or feeling towards it. With most other processes the image is something which “appears”, but in gum it is something which is to a far greater extent “contrived”.