Gum Bicromate Print
Frauke Hänke/Claus Kienle, Hamburg, Germany 1993 (pdf)
Gumgraphies don't give proof of documentary evidence which is characteristic of conventional photography. By using formal means - as among others colour, texture or materiality - a subjective image of reality is created. At the same time the onlooker will be inspired by these formal elements to have associations.
Gumgraphy is a photographic technique at which the positive material itself is coated by the artist(contact printed). The light-sensitive layer consists of gum arabic, chromate salt and pigments. For example drawing paper, cotton or wood can be used as base material. This will first be prepared by applying a mixture of gelatin which causes the pigments to remain on the base material surface rather than sinking in. The coated material will be exposed in daylight or ultraviolet light under a same size negative. The bichromate causes the gum arabic to harden in proportion to the amount of light received. After exposure, the print is placed in water, where the part of the gum that remained soluble slowly dissolves and sinks to the ground.
During the exposure interventions are possible in order to infl uence the picture. A positive of little contrasts is the result of the first process of exposure. It is only by repeating the copy process, by which the base material will be coated again with the light-sensitive emulsion, exposed and developed, that the picture will develop tonal values. At this process the contrast as well as the color can be varied with each new layer. Using the gumgraphy one is conscious of the particularities and "mistakes" of this technique which, however, are integral part of the working method. Gumgraphy is based on the historical technique of gum bichromate print (ca. 1895-1930).