Handcrafted Gum Bichromate prints
A recent 3 colour gum bichromate print. (some say Dichromate, some say Bichromate)
The gum bichromate process, is a 19th-century photographic printing process based on the light sensitivity of dichromates, which is nasty stuff to work with and these day’s difficult to get a hold of without a licence. Gum Bichromate is capable of rendering painterly or photographic images from photographic negatives. A sheet of watercolour paper is coated with a sensitiser: gum arabic, ammonium dichromate to make it light sensitive and a watercolour pigment for the colours, exposed through 3 CMY separation negatives and processed. The image is built up in three layers/passes, (sometimes as many as 11 layers), one for each of the process colours Cyan, magenta and yellow.
When the coated paper has dried, it’s exposed in contact with each separation negative ( separately ) to ultraviolet light. It’s usually a good idea to have some kind of registration system to make sure that the negatives are positioned correctly for each layer. My print below looks mainly like a photograph with a slight painterly touch. I have posted 3 images, one of the mounted print, one of the print in it’s 3 stages of the process, Cyan, Yellow and then with the final layer of Magenta, the last image is me holding the print next to the original digital file on the screen.