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Here is my recipe for sensitizer for bleach develop:
Gum pigment solution:
100 cc of 14 Baume commercial gum 2.5 grams of Daniel Smith carbon black powder, 4 drops of jet dry. Jet dry is an automatic dishwasher rinse aid. I found this detergent very helpful in dispersing carbon black powder, which is difficult to wet. Jet dry is a miracle detergent for me to help with coating, reduce bubbles, etc.
All that mixed in a mixer for a few minutes. Last batch (0.5 liters) was made several months ago. I just shake it before using.
I call it a 2.5% carbon solution, although in reality it is higher, since gum density is less then 1.
Preparing sensitizer:
12 cc of gum pigment solution, 12 cc of water, 6cc of 30% ammonium dichromate. This gives me the right consistency for my coating method. It is also optimum in terms of having enough water to wet the paper and keep it moist long enough to smooth the coat, but not to keep it too wet. My paper has been Fabriano Artistico white and extra white since my first tricolor gum a few years back. When sized both papers act in the same way. I suppose I am so addicted to that paper that if they ever stop making it I'll have to quit printing.
Sieze is two coats of 3.5% gelatin hardened with glutaraldehyde or recently with dichromates. The examples on the web site were made on paper hardened with dichromates.
Exposure is 3 minutes under UV BL light bank. My typical gum exposure is 45s to 1 minute.
Development:
Soak briefly (1-2 minutes) in water to remove dichromates. Soak in bleach solution (20ml of bleach/liter) for 1 to 5 minutes, finish developing in water. 30 minutes to 2 hours are my typical times for water development. If development is very slow go back to bleach for a few minutes. I change or replenish bleach every 2 or 3 prints.
Have fun printing
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