ABSTRACT
Gum printing makes water-soluble pigments, such as gouache and watercolors, photographic, producing prints of subtle and wide-ranging colors on paper, ceramics, or fabric. Gum arabic, paint, and a solution of ammonium or potassium bichromate as the light sensitizer are mixed to create a single or multicolored image ranging from continuous-tone to high-contrast. Gum printing also can be combined with traditional printmaking processes such as etching and drypoint, or with other photo-printmaking techniques. One of the earliest photographic processes to be used as a personally expressive medium, gum bichromate—also known as dichromate—printing is usually credited to a Frenchman, Alphonse Louis Poitevin, whose 1855 patent, based on experiments using carbon, were founded on tests with the light sensitivity of dichromates by earlier inventors. Bichromates can cause skin inflammation, similar to an allergic reaction, upon repeated exposure. Bichromates can be poisonous when ingested, even in small quantities.
