Metabisulphite as stop bath.

Discussion in 'B&W: Film, Paper, Chemistry' started by john_s, Sep 20, 2007.

  1. john_s

    john_s Subscriber

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

    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. Dave Miller

    Dave Miller Member

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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.
     
  3. juan

    juan Subscriber

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    I use citric acid when I use stop bath.
    juan
     
  4. Les McLean

    Les McLean Subscriber

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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.
     
  5. john_s

    john_s Subscriber

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    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. lee

    lee Member

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

    lee\c
     
  7. Photo Engineer

    Photo Engineer Subscriber

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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. Photo Engineer

    Photo Engineer Subscriber

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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. john_s

    john_s Subscriber

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    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. Photo Engineer

    Photo Engineer Subscriber

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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
     
  11. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I use a 1% metabisulfite solution in my tank line with Acufine and TF-4 (until I run out, and then I'll switch to another alkaline fixer), but I just measured the pH, and it's just about 2.1, so still quite acidic, if my pH meter isn't too far out. Maybe I should increase the dilution in the interest of maintaining the fixer. After a few years, I haven't had a problem with this.

    It doesn't have as strong an odor as acetic acid stop, so that's a plus.
     
  12. RalphLambrecht

    RalphLambrecht Subscriber

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    then why do itand not leave it out?
     
  13. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    When I don't use a stop, I use a water rinse, and I use it to prolong the life of the fixer.
     
  14. john_s

    john_s Subscriber

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    Since I started this thread in 2007 I offer this update. I now use a very dilute metabisulphite stop for FB paper, on the basis that it's more compatible with neutral fixer (Kodak Flexicolor Fixer, pH close to neutral, not very smelly) than acetic acid. The metabisulphite stop smells of SO2 but in a Nova slot processor it's not too bad. The occasional staining no longer occurs.

    The metabisulphite solution does not seem to last long, so I replace it during a long session. It's very dilute, but as David Goldfarb notes above, still rather acidic.
     
  15. Gerald C Koch

    Gerald C Koch Member

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    The only problem would be the sulfur dioxide that the metabisulfites release. Some people are sensitive to this gas which can cause asthmatic symptoms especially in a closed environment such as a darkroom. A better choice would be citric acid.
     
  16. juan

    juan Subscriber

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    Jerry, do you have an idea of how much citric acid would be best for film? I use it for paper, but have never been really careful about how much there - a couple of teaspoons in a tray of water. I would think film would be more critical.
    juan
     
  17. Gerald C Koch

    Gerald C Koch Member

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    Of the organic acids citric acid is quite strong and also contains three acid groups as contrasted to acetic acid's one. A concentrate can be made up by dissolving 300 g of citric acide in enough water to make one liter. For use it is diluted 1+19. Fiber based papers should be treated for 30 to 60 sec.
     
  18. RalphLambrecht

    RalphLambrecht Subscriber

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    i use a 2%solution for paper and a 1%solution for film.
     
  19. Photo Engineer

    Photo Engineer Subscriber

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    I was told not to use Citric Acid stops with color materials. The reason escapes me now, but that is what I remember.

    PE