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Gum printing, developed in 1839 by Mungo Ponton, is one of the earliest photographic processes for creating an image on paper.

The process takes advantage of the fact that a wet mixture of gum arabic and potassium dichromate coated onto a sheet of paper will harden and become relatively insoluble by water when exposed to light.

The full process works as follows:

  1. coat a sheet of paper with a mixture of gum arabic and potassium dichromate.
  2. place a negative over the paper.
  3. expose the negative/paper sandwich to light.
  4. wash off the parts of the mixture which are water soluble (i.e. the parts of the mixture which the dark areas of the negative prevented being exposed to the light).
The result is a positive image of the original.

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