Tuesday, March 24, 2009

gum bichromates

photo by Karl Gerling

Please join us on April 5th @ 1:00 and explore the photographic process of gum bichromates. Gum bichromate (or dichromate) is a photographic printing process that involves creating a working emulsion made of:
  • gum arabic
  • a dichromate (usually ammonium or potassium)
  • pigment

The light sensitive emulsion is spread on paper and allowed to dry. Negatives or objects (in the case of a photogram) are then laid on the coated paper and exposed to a UV light source. The light source will harden the dichromate in proportion to the densities of the negative. After exposure, the paper is washed in a series of water baths and allowed to develop until the unhardened portions of the emulsion have dissipated. Voila!

Participants will learn to mix chemicals, coat papers, and print from negatives/transparencies, and how to make photograms. Folks will also receive an instruction packet, a frame for printing, and paper.

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