The gum bichromate process is a printing method that stands at the crossroads of photography and printmaking, expressing itself in painterly terms. Introduced in the middle of the 19th century, it experienced a surge of popularity during the Pictorialist period of photographic history from 1880 to 1920. It resurfaced along with several other hands-on printing processes in the 1970s and remains one of the ennobling processes.
Beginning with an enlarged black and white negative, gum bichromate photographs are made by coating non-photographic paper with a mixture of tree sap, pigment, and potassium dichromate. Gum arabic (the tree sap), derived from the acacia tree, a colloidal agent, holds the light-sensitive dichromates and pigments together. I mostly use mineral pigments taken from the earth (Italian and German soils are favorites) but other materials round out the palette – things like walnut hulls gathered from nearby woods, turmeric from the kitchen, and others imported from afar like sandalwood and indigo.
I make these prints by brushing the pigmented mixture indoors, attaching the black and white negative, then exposing the print to sunlight outdoors or a bank of UV lights in my darkroom. During exposure, gum arabic is transformed from a water-soluble to water-insoluble material according to the amount of light received. After exposure, the negative is removed and the print is then placed face down in a tray of water, allowing the least exposed areas of the print to fall away from the brushed surface. When “enough” pigmented mixture has fallen off, the print is hung out to dry. This process is then repeated on another day using other pigments. Most images take a week or more to create. Most are printed more than three times and upwards of a dozen or more times, resulting in a full-scale print of beauty and permanence.
In the 19th century, what a photograph looked like, what it was made from, and how it was created was very much a personal, creative decision. By 1900, expediency would settle on silver gelatin as the standard of the industry and the dozens of other photographic methods developed in the first years of photography were abandoned.
The wide variety of alternative photographic processes has fascinated me for years and I have experimented with many of them. In the gum bichromate process, I find a method of making photographs that is flexible, somewhat forgiving, has excellent surface qualities, and a beautiful finish.