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  1. #11
    esanford's Avatar
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    Quote Originally Posted by Ole
    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.
    This may be a scientific truth, but I have been using 2% acetic stop bath for 20 years and I have not reticulated a film or damaged an emulsion... I don't use indicator stop bath because I don't trust it. The key is dilution. I dilute stop bath for films 1:31 with 2% acetic acid. Stop bath for prints is diluted 1.5:31. I am very careful to make sure that the stop bath and fixer are all +- 3 degrees from the developer. Stop Bath is discarded after every film or print developing session. Reticulation is caused more by the difference in the temperatures then any other source. I only use FB paper so I don't know the impact on platic resin coated papers.

    Getting to the question, I use a stop bath because it halts the developer. If I develop something for 2 minutes, I want 2 minutes... not 2 minutes and 10 seconds or 20 seconds. That level of precision lets me isolate other problems. Finally, the stop bath extends the life of the fixer... especially for prints. With films I develop no more than 7 rolls of film in one quart of fixer. With prints, I process no more then 75 prints in 1 gallon of fixer. I got this routine from Fred Picker's Zone VI workshop... A 30+ year old text that is still worth having....
    Often wrong, but never in doubt!

  2. #12

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    Quote Originally Posted by Ole
    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.
    Here's what it says on the bottle of "Sprint BLOCK Stop Bath (buffered, vanilla-scented, with indicator)", the stuff I use:

    "In conventional stop baths, the acid ingredient which stops development is hazardous and unpleasant to use, and can damage prints. Acid can break down print sizing which normally protects fibers from fixer thiosulfate contamination, a major cause of deterioration. Plain water stop baths eliminate the side-effects of acid, but do not stop development as effectively, and can cause stains, emulsion swelling and reticulation.

    BLOCK is an acid solution, but the acids are buffered to minimize the side-effects. Buffering protects print filbers for greater permanence, reduces emulsion swelling, staining, reticulation, and eliminates odors. BLOCK will also prevent carbonate gas ruptures of films (pinholes) when used as directed."

    Whaddya think, guys and gals?

    Steve

  3. #13
    Ole
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    Apart from the alleged "can cause stains, emulsion swelling and reticulation" from water bath, that's about what I think about acetic acid stop baths too. Well - I have my doubts about the deletorious effects of stop bath on sizing too...

    Block seems good - buffered, moderate pH (about 5.5 to 6?) - they've even added vanilla scent (to camouflage the characteristic smell of the main ingredient?)!

    But I still think I'll stick to my citric acid when I need a stop bath - a 25g pack lasts a very long time!

    As to short developing times: This is really the same thing as my lith printing, a need to stop immediately. But paper should be developed to completion (usually at about 2 minutes), and all the film/developer combinations I use are a lot slower.

    I'll round this off with a little "alternative stop procedure": Don't.
    I developed Maco IR 820/400 in Neofin Blau for 20 minutes, then ended the processing by pouring in a tot of 60% ammonium thiosulfate. Negatives were just great - no "stains" or "reticulation" or problems with "emulsion swelling" either! And no pinholes - which is a danger when using carbonate developers and acid stop baths!
    -- Ole Tjugen, Luddite Elitist
    Norway

  4. #14
    Ed Sukach's Avatar
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    I think a great deal of the "troubles" usually connected with an acetic acid stop bath are a result of using too strong an acid concentration. However, I do NOT use any acidic or otherwise stop bath in film OR print processing, with one great exception: I've found it necessary between color development and bleach-fix in RA-4 Color Print processing - otherwise uneven development, streaking, and assorted other miseries seem to occur. In that case, I use 1% acetic acid -- made by diluting common 5% "strength" white vinegar 1:4 with water for a 1% acetic acid solution. All my work is "one-shot" anyway, in a JOBO processor.
    Diluting white vinegar with water - now we are talking CHEAP!!. As for the smell of diluted white vinegar - is there a smell? Certainly, I`ve used far stronger concentrations on my salads, and I've encountered stronger in one of my favorite foods - sill/i - pickled herring.
    Carpe erratum!!

    Ed Sukach, FFP.

  5. #15
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    There should be no problem with todays modern films if you use an acid stop bath. In fact, the acidity reduces the severe swell induced by the developer. Modern films have their minimum swell at about pH 4.5, the isoelectric point of gelatin. Swell is high on the alkaline side, and high below about pH 3.5.

    Swell is optimum and moderate in neutral and alkaline fixes, allowing faster fix and wash times. (see for example, specs for TF-4 and RA C41 fix)

    Acidification before an acid or neutral fix is said to reduce the potential for fixer stain and formation of dichroic fog in some fixers.

    If you use an acid hardener fix, you can precipitate the alum out of the fixer onto your film or paper by going from developer to water to fix. The alum is difficult if not impossible to remove and can be seen as a white crust or sheen on negatives or prints. So, a stop bath is really a good idea with acid hardening fixes.

    It has also been shown that uniformity in negatives and prints is somewhat better when a stop bath is used after the developer. The best example illustrating that is with the RA paper example above. Uniformity is best with a stop after development and before the blix. On large prints and LF or MF negatives, you can often see nonuniformities, streaks or mottle in large areas of uniform density.

    The only exception I have seen to this is in the C41 process where the development is slow (considering temperature) and the bleach is very rapid compared to development. A stop is not needed in C41.

    PE

  6. #16

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    Quote Originally Posted by Ole
    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.
    Have you tried a sodium sulfite stop? You know how
    incompatible is the lith process with more than a
    trace of sulfite.

    The little lith printing I've done has had no "snatch"
    point; no suddenly done. So, as with any printing done,
    it's from developer and into the VERY dilute one-shot
    fix I use. A. or S. Thiosulfates, unadulterated, are
    ph near neutral.

  7. #17
    Bob Carnie's Avatar
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    I print a lot of lith prints, and as Ole suggests I require an immediate stop of development . I get this with an acid stop bath and this would be my main concern with the stop stage.

  8. #18

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    Quote Originally Posted by Bob Carnie
    I print a lot of lith prints, and as Ole suggests
    I require an immediate stop of development .
    I process as Ed processes save for my one tray being the
    one tube he uses. We both one-shot all chemistry and
    have no use for any sort of stop.

    The sodium sulfite stop may be faster than an acid stop.
    Faster still I'd think would be a sodium bisulfite stop.
    A 50/50 blend of the two may be acid enough.

    Actually I don't credit any chemical in a stop with
    more than a trace of involvement. After all, stop baths
    run, comparatively, about 49 parts small, light weight,
    swift moving H2O molecules and 1 part large, heavy,
    slow moving something else. An immediate dilution
    AND sudden drop in ph can be expected from
    water alone.

    BTW, I've gotten swamped with indoor and outdoor
    upgrades this summer and not been able to do the lab
    work I thought I'd be doing. I'll be less interrupted for
    having that work out of the way. Dan

  9. #19
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    Dancqu
    With one shot I would imagine you would be ok for not using a stop bath, for me I use a lot of chemicals per printing session. 12 litres lith dev, 10 litres stop, fix a- 8 litres, fix b -8 litres, I suspect by using a stop I am helping out my fix a . I have found that without the acid the lith print will indeed travel more than I would like. ( I know this because I forgot the acid in my stop tray one session and I could not figure out why I was getting streaking until I checked the Stop.

  10. #20

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    Quote Originally Posted by Bob Carnie
    I have found that without the acid the lith
    print will indeed travel more than I would like.
    Your lith processing vs a Jobo type one-shot conventional
    print processing; it's an apples and oranges sort of thing; a
    few ounces of chemistry used one shot and a two or three liters
    used repeatedly. Also, on one hand development to completion
    and on the other development which is speeding onward.

    Then there is the higher ph of the usual lith developer and
    the hyper-active quinone which actually does the lith. The
    quinone levels build up and the print takes off. How low a
    ph to stop that hyper-active agent?

    I didn't mean to get involved in a lith review. Ole mentioned
    needing acid stop and I suggested sodium sulfite or bisulfite
    or a combination of the two. Sulfite should shut down the
    explosive increase of the hyper-active quinone agent. Dan

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