The Casein Printing Kit from Photographers' Formulary contains pre-measured amounts of the chemicals needed, as well as red, yellow, and blue watercolors, to produce approximately twenty 8 x 10" tri-color gum prints.
Casein is a colloid derived from milk, and when used for printing, the process follows a traditional gum printing method: the colloid is mixed with a light-sensitive dichromate and watercolor, brushed onto paper, and exposed underneath a negative using UV light. After exposure, the light will harden the casein in the thinner regions of the negative and the areas receiving less exposure will wash away in a water bath. For each print this exposure and development process is done multiple times, particularly when making tri-color prints that require separate red, yellow, and blue exposures.
- Potassium dichromate
- Ammonium caseinate
- Sodium benzoate
- Red, yellow, and blue watercolors