bromoil bleach for the timid
I was wondering......
Is it necessary to use hydrochloric acid or sulfuric acid when making a bleach solution? I'm not a chemist and am very reluctant to try mixing these. Is there such a thing as a pre-mixed bleach that can be used for bromoil, or is there another recipe that is a bit safer? I have an Ohaus triple gram (?) scale for mixing dry chemistry, but the acid scares me a bit.
I love the look of bromoils and would really like to try it.
Also, what is the recommendation for exhaust systems? I manage to get along with out it while using selenium/sepia split toning in an 'open' basement without too much trouble and am wondering if there is an issue when mixing bromoil bleach.
Thanks in advance.......
From where have you your recipie?
I have never heard og adding any acids to the bromoil bleach... (unless I am from Denmark, and not understanding anything...)
I use (from memory): potassium bromide - copper sulfate and potassium dichromate...
(My recipie is slightly different than the one ex Gene Laughter uses, as I am doing this using liquid emulsions as matrix'es and not "normal" paper (can't seem to get it to work)
Care should be taken with especially the dichromate! (don't inhale - drink - eat - touch it... - use it in a well ventilated place. AND when disposing it - don't pour it in the sink... it is very damaging to the water inviroment...)
I found an old (1943) publication by "Camerette" Photographic Series called "Bromoil Printing Made Easy" by Hugo P. Rudinger which gives a bleach formula:
20 drops of pure sulphuric acid in 12 1/2 oz water. Then dissolve the following in the order given:
Copper Sulphate 1 oz.
Potassium Bromide 1 oz.
Potassium Bichromate 25 grains.
Then he goes on to say "This gives a stock solution which, for use, is diluted 1 part solution to 4 parts water..."
Some say the acid assists in softening the gelatin, thus making the matrix easier to ink. I haven't found that it makes any difference in the inking for me. I never use acid in my bromoil bleach. My recipe: 70 mls of 10% copper sulphate. 70 mls of 10% pot bromide. 30 mls 1% pot dichromate. Distilled water to make I liter. Constant agitation for 8 minutes. This mixture will bleach/tan about ten 8x10 matrices.
Thank you so much for your replies. I am really looking forward to this adventure!
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Check the "Darkroom Cookbook". You can substitute sodium bisulfate for sulfuric acid in most bleaches that call for it, although the quantities are fairly large. Sodium bisulfate plus sodium chloride can often be substituted for hydrochloric acid. Sulfamic acid is an often used dry substitute for sulfuric acid. (Warning: sulfamic acid is a strong acid, and it is just as dangerous as concentrated sulfuric. But it is a lot easier to handle.) Cupric chloride in a bleach is an interesting possibility, but I haven't tried it.