At what pH is a stop bath considered exhausted?

Discussion in 'Color: Film, Paper, and Chemistry' started by RattyMouse, Feb 26, 2014.

  1. RattyMouse

    RattyMouse Subscriber

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    I am making my own stop bath and am wondering at what point should I toss it. Is it OK to use as long as it is measurably acidic? (pH <6.0). Or, should it be something stronger, like 5.0 or 4.0?

    Thanks!
     
  2. RattyMouse

    RattyMouse Subscriber

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    Ack!!! I meant for this to be in the b & w forum!! :sad:
     
  3. fretlessdavis

    fretlessdavis Member

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    My understanding was that it needs to be lower than 5.5, but the lower it gets, the higher chance for reticulation/damage.
     
  4. Sirius Glass

    Sirius Glass Subscriber

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    When it gets blue.
     
  5. fretlessdavis

    fretlessdavis Member

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    You can always buy a bulk indicator-- IIRC it's mixed 1:1000, so one bottle will last forever. Pair that with bulk citric acid from a brewer's supply, and you'll have a massive stockpile of Ilfostop for the price of a single bottle of Ilfostop.
     
  6. Athiril

    Athiril Subscriber

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    Bromocresol Purple would be my indicator of choice.
     
  7. Tom1956

    Tom1956 Inactive

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    You can feel it on the print when the stop bath starts getting old. Fresh stop bath make the print feel tacky when you first put it in.After a while the slimy feeling from the developer takes longer to turn "tacky" or "squeaky" feeling, till a point where it stays slimy feeling.. Or the yellow goes brownish on its way to purple. This is not rocket science--you'll know when it's no good any more.
     
  8. markbarendt

    markbarendt Subscriber

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    You do realize that plain old water will work as a stop bath, right?

    The difference is mostly in how fast it stops development, water just takes a few seconds longer than fresh stop.
     
  9. jp498

    jp498 Member

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    Use a non-acidic fixer like tf5 and water is the recommended stop bath. This combination removes most of the odor we associate with darkroom work.
     
  10. Tom1956

    Tom1956 Inactive

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    What good is photography without the smells in the darkroom?:crazy:
     
  11. RattyMouse

    RattyMouse Subscriber

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    If the difference is only 1 or 2 seconds, why does ANYONE use stop bath?
     
  12. Tom1956

    Tom1956 Inactive

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    Because it halts development dead, hardens the gelatin, and protects the longevity of the fixer. Just makes best sense.

    BTW--you could conceivably slice up a cool cucumber from your garden into a bowl, pour in a little stop bath, and sprinkle on a little salt and pepper for some mighty fine eatin'.
     
    Last edited by a moderator: Feb 26, 2014
  13. markbarendt

    markbarendt Subscriber

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    It may take 20-30 seconds instead of 10, so you may pour off your developer 10-15 seconds early say at 9min 50sec, instead of 10min. Sometimes no development adjustment is even needed.
     
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  15. markbarendt

    markbarendt Subscriber

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    Hardens the gelatin, sure about that?

    As to protecting the fix water does the same thing, just takes a hair longer (and smells better).
     
  16. Tom1956

    Tom1956 Inactive

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    Hardens it more than it was while it was in the developer. Though I wouldn't go so far as to call it "a hardener".
     
  17. Xmas

    Xmas Member

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    the imperative reason for an acidic stop bath is to reduce the probability of stains with some developers... Real horrible with a print. It does reduce alkaline carry over into fixer as well.

    with non prehardened film or plates you might have used a hardened bath.

    with non prehardened film you run more risks of reticulation with an acid stop manufactures would caveat this...

    Ansell A and Barry Thorton used a borax post bath with film cause an 'instant' stop was not what they wanted

    web gossip is wonderful stuff
     
  18. flash26c

    flash26c Member

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    Besides the fact that it is so cheap, why chance anything, dump it after you're finished.
     
  19. BradS

    BradS Subscriber

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    Ratty, you're really over thinking this. Plain tap water works just fine....Kodak indicator stop bath is exhausted when it turns blue (instead of dark yellow) but, I never keep it that long.
     
    Last edited by a moderator: Feb 27, 2014
  20. Tom1956

    Tom1956 Inactive

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    I'll never agree with the "plain water stopbath" people. I always liked Kodak's way.
     
  21. RattyMouse

    RattyMouse Subscriber

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    I'm not over thinking this. You guys are! :laugh:

    I'm looking for a number. At what pH is stop bath considered exhausted? Give me a number. That's all I want.
     
  22. markbarendt

    markbarendt Subscriber

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    Okay, we might be overthinking, but if that's true then you are under thinking it. :whistling:

    There isn't an exact answer.

    The stop doesn't just quit working at a given PH. The first film or paper that is run through the stop is going to stop really fast, next one a bit slower, slower again for the next:it's a progressive change. If you are using indicator stop it is my understanding that when it turns color it has essentially reached a point where "it is as effective as water" and some of us think water is effective.

    So you need to define what "exhausted" means.
     
  23. MartinP

    MartinP Member

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    As the function is to lower the alkaline pH of the developer and stop it's actions, then one also needs to consider the developer and the size of the print and trays, as well as the pH of the second-bath (with water being more-or-less neutral, pH7).

    With a small print it is relatively easy to give evenly fast submersion and vigorous agitation to the whole print surface, while with a larger print this becomes much harder to to achieve perfectly -- in water, working by massive dilution of the carried-over developer, that could mean a visible difference from one area to another. An acidic stop-bath does it's job chemically and hence much more quickly than the dilution action of water.

    Whether this is significant depends on the print, the developer, the critical standards of the printer and the use to which a particular print will be put. So, as usual, the correct answer to the question is "it depends".
     
  24. Jaf-Photo

    Jaf-Photo Member

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    The classic stop bath is acetic acid diluted in water to 0.7 percent. This is a very cheap liquid that you could reuse a few times and then toss and replace.

    The benefit over water is that you stop the dvelopment instantly and uniformly across the negative, which provides greater control and consistency.
     
  25. RattyMouse

    RattyMouse Subscriber

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    Does the indicator flip at 7 or is it higher?
     
  26. Anon Ymous

    Anon Ymous Member

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    The indicator is bromocresol purple and it doesn't "flip", it's a gradual transition. Have a look here. I toss it when it has that dirty colour, about pH 6. It's still acidic.