gum dichromate

Definition: Printing process based on sensitised gum arabic carrying coloured ink. * Gum arabic (water-soluble glue from acacia tree) is sensitised with potassum dichromate. When paper coated with pigment-dyed sensitised gum is exposed by contact to a negative, unexposed areas are soft and can be washed away by hot water, leaving hardened, coloured areas behind. The result can be re-coated with another layer, with a different colour. * Obsolete commercially, but various forms revived for art and special effects.

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