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  1. #11
    gandolfi's Avatar
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    Quote Originally Posted by cliveh View Post
    Try this -
    1) A possible formula for a one part bleach/tanning solution is as follows: -
    Copper Sulphate 113 gms
    Potassium Bromide 113 gms
    Potassium Bichromate 5 gms
    Sulphuric Acid concentrated 6 gms
    Distilled Water to make 1.8 lt
    Clive: I have to ask: why add Sulphuric Acid to the bleach?


    UPDATE: I just inked the two images shown in my first post.
    They actually ink well - a little harder than usual, but they do recieve the oil as planned. I am happy with the results for two reasons:

    1: I like the images... ;-)
    2: Even though they sometimes seem not to have been bleached anough, I should't worry - they are still good for bromoil inking..

    When the images are dry, I'll make a quick snap and upload it..

  2. #12
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    Quote Originally Posted by gandolfi View Post
    Thanks PE. That does make sense.

    But it doesn't explain why it looks like the image isn't bleached away. It is not that the bleach is exhausted I think, as the deepest blacks are gone - but the "middletones" and highlights seems to stay..
    What you are seeing is a partial image of Silver Sulfide that remains behind due to extremely high density in original Silver metal. If it is Ag2S, it cannot be removed.

    My guess anyhow.

    PE

  3. #13
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    Quote Originally Posted by gandolfi View Post
    Clive: I have to ask: why add Sulphuric Acid to the bleach?


    UPDATE: I just inked the two images shown in my first post.
    They actually ink well - a little harder than usual, but they do recieve the oil as planned. I am happy with the results for two reasons:

    1: I like the images... ;-)
    2: Even though they sometimes seem not to have been bleached anough, I should't worry - they are still good for bromoil inking..

    When the images are dry, I'll make a quick snap and upload it..
    It helps to control the correct pH of the entire solution.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  4. #14
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    Actually, all Dichromate or Permanganate bleaches must be acidic and must be acidified with Sulfuric Acid. This is because the Silver metal must be converted to Silver Sulfate which begins dissolving in the water. These cannot be rehal bleaches and work with any great efficiency.

    PE

  5. #15
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    But if all bromoil bleaches must be acidic - then why does some of the recipes show no acid? As far I have understood it, the function of the acid is to soften the emulsion to take the ink better. Never heard of the pH function of the acid in this process - in that case, could you substitute it with whatever chemical that balanced out the pH? At what level should the pH be to be optimal?
    “Do your work, then step back. The only path to serenity.” - Lao Tzu

  6. #16
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    Jerevan;

    I can only say that dicrhomate does three things. It bleaches silver, it softens gelatin in acid, and it tans gelatin imagewise. Whether all 3 of these are of equal importance or whatever, here, IDK.

    PE

  7. #17
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    Jerevan and PE: interesting. I have never seen a ewcipie for bromoil printing that contains acid...

    And as it might work well for "normal" papers, I don't dare to use it for liquid emulsion papers. The emulsion is soft enough as it is, and I fear, that softer emulsion will make inking impossible....

  8. #18
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    There is one in Derek Watkins book, the Gilbert Hopper one and that one is with 10 ml of a 10% solution of sulphuric acid. Emil Mayer also gives a recipe, but with hydrochloric acid. From what Emil says, heavy silver deposits may not bleach fully. And when doing liquid emulsion I guess it would be possible to get these thicker deposits. All of this is theory and reading - I have only used the non-acid bleach, on Foma papers.

    On a related note, some of the sensitizer recipes for oil printing contains citric acid.
    “Do your work, then step back. The only path to serenity.” - Lao Tzu

  9. #19
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    The proof of the pudding is in the eating and I should imagine there are probably as many different ways/chemical formulations for Bromoil as there are people who make Bromoils. I suppose it's what works for you.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  10. #20
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    I would have to agree with cliveh. If it woks, why worry. But then Jerevan's comment about silver not bleaching completely is in line with my original comment. I think there is either too much silver or overdevelopment for the bleach you are using.

    PE

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