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One of the most versatile Alternative Processes, Gum
Bichromate was invented in 1855, and became popular at the turn of the century.
The process takes advantage of the fact that colloids, such as gum, gelatine and
glue, when mixed with a bichromate, become hardened and insoluble when exposed
to light. By mixing a coloured pigment in with the colloid, and then washing
away the undeveloped areas with water, you are left with an image in the dye.
Exposure times using daylight will be typically between 30 seconds and 2
minutes. Advanced Gum Bichromate workers build up a number of layers of varied
pigment colours by re-sensitising, re-exposing and re-developing
prints.