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  1. #31
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    Quote Originally Posted by Michael R 1974 View Post
    I've never used it until it even had a chance to change from its initial bright color. The odor is a poor reason for not following Kodak's dilution instructions. There are odorless stop baths if one finds the odor objectionable.

    I'm also wondering why Kodak doesn't put Bromocresol Green in rather than Purple.
    Michael:

    Don't you mean "colour" and "odour" ?

    I actually use Ilford's citric acid based stop bath with prints because of the odour.

    I use Kodak's acetic acid based stop bath with film, because it is much more concentrated, and therefore both easier to store and therefore in the long run less expensive in use. As it isn't sitting in trays the stronger odour doesn't matter as much.

    And as for the indicator colour itself, could it be that a green indicator would be harder to see under safelight illumination?
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  2. #32

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    I believe that bromcresol purple was chosen since under an amber safelight the stopbath would appear uncolored if OK and black if it was exhausted.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  3. #33

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    Makes sense - although it should work the same way with bromocresol green, which goes from yellow (fresh) to green to blue when it's wasted. I thought it might be a better indicator only because its pH range is narrower (3.8-5.4), being yellow below at 3.8, transitioning to green ~4.5, and to blue at 5.4.

    Matt - haha. Yes of course I meant to add those extra letters but American is quicker.

    Gerald - as far as you know is Kodak Indicator SB just acetic acid with the indicator?

  4. #34

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    Quote Originally Posted by MattKing View Post
    Don't you mean "colour" and "odour" ?
    Thanks to Noah Webster, no. We also spell grey as gray and theatre as theater. We pronounce schedule so that it agrees with school. Some think Webster didn't go far enough in regularizing English spelling and pronouciation. George Bernard Shaw was even more radical in his recommendations. Still we muddle on and manage to understand one another. Of course, there are always the the australians!
    Last edited by Gerald C Koch; 08-06-2012 at 07:16 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  5. #35

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    Yes, Kodak Indicator Stop Bath is just acetic acid and bromcresol purple.

    For an indicator stop bath the only real requirement is a color change below pH 7.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #36
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    Quote Originally Posted by Gerald C Koch View Post
    Thanks to Noah Webster, no. We also spell grey as gray and theatre as theater. We pronounce schedule so that it agrees with school. Some think Webster didn't go far enough in regularizing English spelling and pronouciation. George Bernard Shaw was even more radical in his recommendations. Still we muddle on and manage to understand one another. Of course, there are always the the australians!
    Sorry Gerald - that comment about spelling was really addressed just to Michael.

    Those of us in the Commonwealth have to stick together, you know.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  7. #37

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    Quote Originally Posted by Gerald C Koch View Post
    Once the SB turns purple the bath is at a pH of 6.8 or higher. Pure water has a pH of 7. When the stop bath is purple it is no longer a stop bath but a water rinse. If you wouldn't use a water rinse in your processing then you shouldn't do this. What you describe is a false economy.
    Still, at a PH of 7, water is 5000 times more acidic than a developer at PH 10.5.
    Given the volumn differences of a bath vs a sheet of wet paper, I have always wondered how much of a PH shock is required, or how low in PH does developer stop working.
    I could only find a reference for hydroquinone,for which there are two pH values whereby a dramatic increase in activity results. The two values are 10 and 11.6, suggesting below 10 and it doesn't work so well.
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  8. #38

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    Quote Originally Posted by Gerald C Koch View Post
    Yes, Kodak Indicator Stop Bath is just acetic acid and bromcresol purple.

    For an indicator stop bath the only real requirement is a color change below pH 7.
    Not according to the data in Haist. Depending on the total acidity of course, the time to halt Dektol goes way up as the pH increases past 5. Based on the data (from Henn/Crabtree) if the SB turns purple at 6.8, it has long since become relatively weak and the typical stop bath times running 30 seconds or less are way too short. Granted Dektol is a more active developer than most film developer working solutions and the original data was from 1951 when emulsions were different.

    So, a question: given the emulsions of current films and papers (by the major manufacturers - not the old-style junk), is the conventional rule of not using an acidic stop bath with moderate pH carbonate-driven developers still valid?

    For example, I recall a similar thread in which PE commented on the buzzing/hissing you sometimes hear when transferring a sheet of paper from Dektol to an acetic acid stop bath, saying that it didn't appear to cause any problems. However I'm curious about the effects on current hardened films when going from a carbonate developer to an acetic acid stop bath with a pH of 2.8-3 (eg fresh Kodak SB). Perhaps it is no longer something to worry about. Not sure.

  9. #39

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    Michael,

    My answer was directed toward what was in the Kodak product not whether the particular formulation was affectatious. Kodak uses bromcresol purple which changes at ph 6.8. Any indicator which changes near this point could be used to duplicate the action of kodak's product. In another post I did mention that when the solution turns purple it is already past its usefulness. The poster said that he ran a few prints through his stop bath even though it was purple. My response was that this was not a good idea.

    I personally have used only a water rinse for film for over 20 years and never experienced any problems. No fog, no staining, no nothing. Too much seems to have been made on APUG with the idea that development must be stopped immediately or something bad may happen. In a stop bath two things happen either of which is necessary and suffieicient. First the developer in the emulsion is diluted by the stop bath. Second the pH in the emulsion is lowered stopping developer activity. However, the main purpose of a stop bath or rinse is to avoid transfer of alkaline developer to the fixer. For typical development times a few more seconds of development is not going to be even noticeable.

    For FB papers I do use an acid stop bath because the paper acts like a sponge and holds more developer. Modern emulsions are hardened more than older style ones. I doubt if the dreaded pinholes are a problem with such films. In addition most modern film developers do not use a carbonate buffer.

    Jerry
    Last edited by Gerald C Koch; 08-07-2012 at 12:49 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  10. #40

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    Makes sense, Gerald. Haist may have overstated the risks of uneven development with water instead of acid. Not sure - and again, the materials at the time may have been more prone to problems.

    One thing for sure, the mechanisms of acidic stop bath function, and the variables involved are taken for granted by most photographers. It's interesting how often people ignore the instructions in the case of Kodak SB, modify the dilution without understanding the effects, or make substitutions with vinegar, citric acid etc without measurements. We are all obsessive when it comes to developers, but the stop bath is often just a rough acid mixture.

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