Ratios and exposure times

February 21, 2012

nonetodate asked: I have enjoyed the gum work and discussion.  

I do have a few questions regarding your process:

What amount of pigment do you put into the gum and how much gum is used?

Do you vary this ratio depending on the pigment color?

Do you use the same exposure time for each color pigment or do you vary it when you’re doing those multi layer prints?

Thanks.  Starting with the Magenta negative I mix equal parts (1:1) of Ammonium Dichromate sensitizer with Gum Arabic (12 dropper stems of each or 12:12) and about and inch of pigment (Schmincke Pthalo Blue for the cyan, Permanent Carmine for the magenta and Cadmium Yellow Middle for the Yellow).  I don’t change the ratio for the pigment but I do change it to achieve greater contrast (i.e. increasing the Gum to Sensitizer ratio to 13:11 and then 14:10).  I vary the exposure for the different “sets” of layers.  The first set of M, Y & C is a short exposure (no greater than step 3), the second set of M, Y & C is a long exposure (no greater than step 8), the final set is a short exposure again (no more than step 3) and the black is a really short exposure (about 30 seconds).  Actual times may vary depending on the exposure unit you’re using, pigments, negatives etc.  You can check out my post “Gum Bichromate Workflow 2012 ©” from January for photo illustrations of the process.

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