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  1. #1

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    milkish and cloudy fixer

    I'm preparing a normal fixer using:

    1) Water 500ml
    2) Sodium thiosulfate 120g
    3) Sodium sulfite 10g
    4) Sodium metabisulfite 25g

    to this solution I add 25ml/l (12.5ml) of Tetenal Harter (potassium alum based hardener). The minute I add this the fixer turns immediately milkish and cloudy.

    Why?

  2. #2
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    Where do you live? You may have naturally occuring silver in the water. Park City Utah has a major problem with this. Try distilled water and see if that solves the problem.
    Non Digital Diva

  3. #3

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    I have had occasion when adding alum hardner to rapid fixer (ammonium thiosulfate) the alum precipitates. This is usually due to not having the other ingredients completely dissolved and in solution.

    From what you describe, I would think that this may be the problem...if the water supply contained silver, I would think that the precipitation would occur before the hardner is added.

  4. #4
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    Alum precipitates immediately as a white cloudy material, if the solution has a pH value much above about 5.5.

    From your description, this is what is taking place. You can add some 28 % acetic acid to see if it redissolves, but I doubt that it will.

    The pH of an alum fix must be below 5.0 to work.

    PE

  5. #5

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    The milkiness may be sulfurization caused by the solution becoming to acid when you add the hardener. Colloidal sulfur precipitates and cannot be redissolved. The 25 grams of sodium metabisulfite already makes the fixer quite acid and the hardener causes the pH to drop even lower.

    Most manufacturers are now recommending fixing baths without added hardener. This allows the thiosulfate to wash out more rapidly. This is especially true for FB papers where the alum holds the thiosulfate in the paper base.

    If you really think that you need hardener then halve the amount of meta-bisulfite in your formula and see if this helps. You may have to eliminate it entirely.

    When you add the hardener the fixer should be stirred rapidly to prevent local concentrations from becoming to too acid.

  6. #6

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    Quote Originally Posted by Gerald Koch
    The milkiness may be sulfurization caused by the solution becoming to acid when you add the hardener. Colloidal sulfur precipitates and cannot be redissolved. The 25 grams of sodium metabisulfite already makes the fixer quite acid and the hardener causes the pH to drop even lower.

    Most manufacturers are now recommending fixing baths without added hardener. This allows the thiosulfate to wash out more rapidly. This is especially true for FB papers where the alum holds the thiosulfate in the paper base.

    If you really think that you need hardener then halve the amount of meta-bisulfite in your formula and see if this helps. You may have to eliminate it entirely.

    When you add the hardener the fixer should be stirred rapidly to prevent local concentrations from becoming to too acid.

    So, being the role of metabisulfite, to acidify the fixer solution, and being the Tetenal Harter cointain a 28% acetic acid, I have to eliminate the metabisulfite entirely, is that correct?

    Unfortunately I haven't a pHmeter handy; I have to use the hardener because I use it in the b&w reversal process.

    Can I use the Tetenal harter alone, as a pre-bleach bath, to fight against the swelling of the gelatine in the following permanganate-based bleach bath?

  7. #7

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    Quote Originally Posted by Alessandro Serrao
    So, being the role of metabisulfite, to acidify the fixer solution, and being the Tetenal Harter cointain a 28% acetic acid, I have to eliminate the metabisulfite entirely, is that correct?

    Unfortunately I haven't a pHmeter handy; I have to use the hardener because I use it in the b&w reversal process.

    Can I use the Tetenal harter alone, as a pre-bleach bath, to fight against the swelling of the gelatine in the following permanganate-based bleach bath?
    What is the composition of the bleach bath that you are using?

  8. #8

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    The bleach I'm using is potassium permanganate acidified with bisulfate.
    In particular:

    Part A
    Potassium permanganate 4g
    Water to make 1l

    Part B
    Sodium bisulfate 66g
    Water to make 1l

    I mix 1:1 immediately before use.


    As a sidenote: on photo.net someone is suggesting me that: "No, no! The cloudiness you see is some kind of aluminum precipitate; it's because the pH is too HIGH. You need to lower the pH."

    I'm confused.

  9. #9

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    There's no way that the pH can be too high with the combination of metabisulfite and the acetic acid in the hardener. Take my word as I am trained as a chemist.

    I really believe that you can omit the metabisulfite and use just the hardener.

  10. #10

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    Since I'm perfectionist for nature I wanna understand well what's happening around me, especially in chemistry.
    Are you sure that the cloudy precipitate is colloidal sulfur (H2S) and not alluminium precipitate?
    Excuse me if I'm hammering you on this (insignificant point).

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