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  1. #1

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    Stop bath for printing - water or something else?

    When developing film I use a water stop bath and this works well. Is there any reason not to use a water stop bath for paper (both RC and fibre based) when printing?

    I did a search of the archives looking for an answer but nothing came up. Any thoughts gratefully received.

    Paul

  2. #2

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    Prints have the potential of carrying much more developer to the stop bath. Since you are planning on using water, you will quickly contaminate the water bath and then transfer developer to the fixer. This will lead to rapid deterioration of the fixer.

  3. #3
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    I also tend to use water as a stop in dveloping film, but an indicating acid stop when printing. There are several reasons for this.

    First, one of the main reasons for a stop is to provide a means of adjusting the pH of the film between developer and fix. Developer is a base, while fix is acid. If you use a plain water stop, it will quickly become a weak base. Then, when you move the print to the fix, the collision between base and acid results in the fix being neutralized. Using an acid stop minimizes this effect and makes the fix last longer. Fixer life is very important when printing because it's so easy to lose track of how many sheets of paper have gone through the bath.

    For this reason, the stop that I use in printing is also an indicator stop that changes color when it approaches a neutral pH. That way I know when it's nearing the end of its useful life.

    Another reason for an acid stop is that it brings the development action to a rapid conclusions. A plain water stop cause the development action to "coast" to a stop - that's fine when developing film, and may actually be advantageous. Paper is much more foregiving that film and can put up with the "abuse". But more importantly, stopping the development action abruptly makes it easier to tone the finished print - if you use a plain water stop, toned prints may have a mottled appearance since the duration of development will affect the visual appearance of the toned finished product.

    Louie

  4. #4
    Ole
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    The only time I use an acid stop is when lith printing. In that one case it is important to stop development immediately at the right point, and nothing does that as well as an acid stop.

    For everything else I use plain water. Paper is developed to conclusion (which it should be in all cases except lith prints), so any developer action in the "stop" - or even the fix - is irrelevant.

    I also use alkaline fix (again: For everything except lith printing), so there is no reason to change the pH from alkaline to acid before the fixer.

    Furthermore: pH has very little influence on the activity of the fixer. Adding alkali to an acid fix will neutralise the pH, but not the thiosulfate!
    If you are really worried about damaging the fixer I will suggest doing without the stop altogether, and replace the fixer as soon as it is visibly brown. That way you will never overuse it.

    In the one case where I do use a stop, I use about 10g citric acid (supermarket grade) in one liter of water. The cost is so low that I make a new one for every session.
    -- Ole Tjugen, Luddite Elitist
    Norway

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    I'm with Ole here. The fix doesn't stop working if it's neutralized, or even if it turns alkaline, as evidenced by the alkaline and neutral fixers out there. It the fix has hardener that may stop working when the ph rises, but you only need hardening in a few circumstances anyway. I use a water tray that I replace every few hours and a neutral fix.

  6. #6

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    Okay guys, I need some enlightenment here. Why should today be any different, right?

    Other than the smell, what's so terrible about using an acetic acid stop bath?

  7. #7
    Ole
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    Quote Originally Posted by seadrive
    Other than the smell, what's so terrible about using an acetic acid stop bath?
    The smell isn't enough for you? :o :o

    Acetic acid drops the pH lower than it should be, increasing the risk of damaging the emulsion due to differential contraction (leading to reticulation). Acetic acid without additives is also poorly buffered: It stops working suddenly.

    Citric acid is "self-buffering" to a certain extent, and also smells much nicer. Gram for gram, the capacity is greater. And I also find it much easier to avoid spilling the little citric acid crystals than to avoid spilling corrosive liquids. But that may be just me...
    -- Ole Tjugen, Luddite Elitist
    Norway

  8. #8
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    I use a water stop for both FB paper and film, with TF-3 (an alkaline fix) for both. No problems with fast fixer exhaustion, or smell

    Murray

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    Yes Murray. It's effective and cheap. I love cheap!!

  10. #10

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    What Ole and Murray have said!

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