dichromate Restrainer for Cuprotype
I received a question about doing Cuprotype without a dichromate restrainer from someone in UK where it is very difficult to get dichromate.
Originally I used Copper II Chloride or Copper II Bromide in the Sensitizer. I settled on Copper II Sulfate as it is least expensive and not hygroscopic. Ammonium Dichromate works well as a restrainer with Copper Sulfate.
I tested hydrogen peroxide, sodium persulfate, and sodium chlorate. None of these worked well with Copper Sulfate. I added 6% Potassium Bromide to the Sensitizer and all these restrainers worked better. The potassium bromide is a less expensive way to get copper bromide in the Sensitizer. The best non-dichromate restrainer was 25% Sodium Chlorate solution.
I am sending photos of step wedges with comparisons of different restrainers vs none.
6% Potassium Bromide
12% Ferric Ammonium Citrate, green
Typical coating for 4x5 inch print
2 ml Sensitizer
1 drop 25% Sodium Chlorate solution
1 drop 10% Tween 20