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  1. #1

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    Metabisulphite as stop bath.

    In the current thread on alkaline stop baths, Photo Engineer made this comment:

    Quote Originally Posted by Photo Engineer View Post
    .............an alkaline stop bath makes the removal of metol and similar compounds more difficult. Amino phenol compounds are not easily removed from coatings in alkaline solutions, and that is one reason to use an acid stop bath. Of course, hydroquinones are harder to remove in acidic solutions. Sulfite assists in their removal though by making sulfonate salts as the HQ oxidizes......
    PE
    I use plain water in a Nova vertical slot processor instead of a traditional stop. It does have to be renewed frequently which wastes water, something I'd like to avoid. I'm considering an acid stop bath, perhaps acetic acid or perhaps Ryuji Suzuki's buffered acetic acid/acetate bath. I'd be tempted to use a more dilute version to minimize carry over of acid into the fixer (which is near neutral pH).

    An alternative stop bath that I've read about is a sodium (meta)bisulphite solution, which is acidic (and smells of SO2 but in a slot processor maybe not too bad). Would the bisulphite be an effective stop and developer-removing agent?

    Has anyone experience in such a stop bath?

  2. #2
    Dave Miller's Avatar
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    Peter Hogan, in his film developing instruction, does suggest using several plain water rinses as an alternative to using his stop bath. It's a method I use for both film and paper.
    Regards Dave.

    An English Eye


  3. #3
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    I use citric acid when I use stop bath.
    juan

  4. #4
    Les McLean's Avatar
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    I've use a water stop bath for both film and paper for years and so far there is no evidence that it has had any effect on the final result.
    "Digital circuits are made from analogue parts"
    Fourtune Cookie-Brooklyn May 2006

    Website: www.lesmcleanphotography.com

  5. #5

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    Quote Originally Posted by Les McLean View Post
    I've use a water stop bath for both film and paper for years and so far there is no evidence that it has had any effect on the final result.
    Yes, I use water too, and I don't have a problem with it. I use a discontinued Nova "Chrome" processor that has running water in slot number 2, very handy. It's surprising how much developer leaches out of fibre paper into the water, which of course is the whole purpose of the wash. But it leads to higher water useage, and here in Melbourne we are becoming increasingly aware of water useage.

    I was looking for something that would reduce my water useage and be more compatible with near-neutral fixer than would acetic acid.

  6. #6
    lee
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    I use water for film and citric acid from a beer making store for paper.

    lee\c

  7. #7
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    Metol is an amine which is basic. It is very soluable in acid and is sold as a salt made with sulfuric acid.

    If you use an acid stop bath, metol forms the acid salt with whatever acid is present in the stop. With a water stop bath, the removal of metol is slower than in acid solution.

    In basic stop baths, it is even slower.

    Use what works, but remember that the stain from any retained chemistry may depend on keeping conditions, wash and time. I have used an acid stop my entire life. I did at Kodak as well. Even if the pH is only 6.5, it works.

    Some community tap water is pH 8 to prevent corrosion. This tap water is less effective than acidic tap water.

    Color developers are even less soluable in water or alkali than are B&W developers. I have seen almost complete retention in some processes and the p-phenylene diamine color developer ends up causing a pink stain in prints or films after several years keeping.

    PE

  8. #8
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    I've been thinking of this. You should know that HQ is more soluable in base than in acid, so we have a double bind here. Metol loves acid and HQ loves base for solubility.

    Sulfite reacts with oxidized HQ to form a more soluable product but regenerates Metol. Therefore this is another problem.

    For those who wish to see this latter take place, if you have CD3, put some in water. It turns cherry red. Now, add a pinch of sulfite and it clears up due to the formation of the CD3 sulfonate. This is the same as happens to many other developers.

    Sulfites are good scavengers for HQ and color developers. I'm not sure about Metol. There are a lot of possibilities there.

    PE

  9. #9

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    Quote Originally Posted by Photo Engineer View Post
    I've been thinking of this. You should know that HQ is more soluable in base than in acid, so we have a double bind here. Metol loves acid and HQ loves base for solubility.

    Sulfite reacts with oxidized HQ to form a more soluable product but regenerates Metol. Therefore this is another problem.

    For those who wish to see this latter take place, if you have CD3, put some in water. It turns cherry red. Now, add a pinch of sulfite and it clears up due to the formation of the CD3 sulfonate. This is the same as happens to many other developers.

    Sulfites are good scavengers for HQ and color developers. I'm not sure about Metol. There are a lot of possibilities there.

    PE
    My print developer contains phenidone and hydroquinone, so metol is not an issue for me. Would a mild acid like bisulphite be a reasonable rinse for my developer: in other words, would the sulphite in it work positively but the acid in it work negatively leading to........?

    I think I'll try it. The smell might make the other questions irrelevant anyway.

  10. #10
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    Phenidone does not react in any significant way to change its solubility.

    Bisulphite would react with oxidized HQ to form the HQ monosulfonate which is much more soluable in water than HQ alone is.

    Other than that, I cannot help.

    PE

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