STOP BATH question !!

Discussion in 'Black and White' started by timothynugent619, Apr 3, 2017.

  1. Hello everyone I have an important question!

    Why cant I use water for my stop bath ? Why do I have to use chemicals?

    Please let me know ! Thanks
  2. Your developer is alcalic. Your film or paper are basically sponges soaked with that soup. Your fixer has to remain a weak acid to be functional. You could use water but it would only wash the developer out / dilute it further. if you have lots of water and feel able to exchange your fixer frequently or even have a Ph meter at hand to check it, go for rinsing instead of stopping.
    I don't mind the chemical nature of 2% citric acid or vinegar.
    timothynugent619 likes this.
  3. A stop bath is not absolutely necessary for film. You can pour out the developer and immediately pour in the fixer BUT you will be hard pressed to get the number of rolls of per volume of fixer stated by the fixer manufacturer. This will not be a problem if you use your fixer 1 shot.
    I use a water rinse between developer and fixer. I fill and dump the tank 2 times between developing and fixer. I have been doing this since 1977 and have never had a problem with fixer exhausting prematurely.
    I use HC110 currently, Xtol, Microdol X, Ronidal, FG7 previously over the years.
    I use Kodak rapid fixer currently, Ilford rapid fix and Kodak powdered fixer in the past.
    The last batch of Kodak Rapid fixer I mixed was anout 16 months ago, have processed about 20 rolls of film in it and it still works as well as the day it was mixed.

    Your results may vary depending on how much film you process and your water supply. I filter the tap water through a Pur filter for mixing stock chemicals and anything important.

    A stop bath for prints is necessary as you want the development to stop immediately.
    timothynugent619 likes this.
  4. Thank you Jochen !
  5. Thank you 13thumbs
  6. It's not carved in stone that you must use stop bath rather than water when processing film, but it will give you better and more consistent results. First of all, in the B&W darkroom, a bottle of indicator stop bath is a valuable chemical. The bath is a solution of acetic acid with an indicator dye that let's you know when it is exhausted. It is usually mixed 1 part to 64 part with water, 2 ounces makes a US gallon in other words. The same mixture is used for B&W films and paper, and reused over and over again. It can last months, or years and when the acidity falls to a level where it cannot stop the alkaline action of the developer, it will let you know and turn a purple colour. Then you start to discard it. Because it is affordable to buy, so inexpensive to use and does what it is supposed to do, that is halt the development immediately - it's pretty clear that it will do a far better job than water will do. The additional bonus is because it neutralizes the alkalinity of the developer on the film or paper, the fixing bath will last much, much longer. Traces of developer left on the film or paper will shorten the lifespan of your fixer.Using an indicator stop bath for both film and paper is a win win outcome. Also, the concentrate and the working strength stop does not deteriorate significantly or at all with time like developer does so it keeps forever. I have been using indicator stop baths (usually Kodak) since 1973.
    allancobb likes this.
  7. I'm assuming you meant "alkaline"?

    For the OP. pH is a measurement of hydrogen ion concentration in a chemical solution. A pH of 7 is neutral. Distilled water has a pH of 7. If the pH is greater than 7 the solution is a "base" or considered alkaline. If the pH is less than 7 the solution is an acid or acidic.

    Developers are alkaline and have a pH greater than 7. You need to neutralize the pH of the developer in film or paper processing before you put the film or paper in the fixer.

    Generally, most people use a stop bath made of acetic acid for this step. You can, however, use water if you provide enough changes in water to wash out the developer from the emulsion prior to putting the film or paper in fixer. The acetic acid stop bath changes the emulsion pH from alkaline to acidic so that the emulsion pH is acidic like the fixer.

    Here's the problems if you don't use stop bath. If you use fixer and put in back in the container to use it again, there are silver compounds that buildup in the fixer. As the fixer gets older with more silver in it, the fixer can react with the oxidized developer in the emulsion. This can cause permanent stains in the film or print.

    The use of stop bath negates this problem as the stop bath neutralizes all of the developer before you put the film or print into the fixer.

    Another problem is shortening the life of the fixer. Fixers are acidic. When the pH changes toward alkaline the fixer becomes less effective. The more alkaline developer is carried into the acidic fixer, the less active the fixer will become as you are very slowly changing its pH from acid to alkaline. You then have to extend the fixing time by some unknown amount to fully fix the film or print because of the reduced fixer chemical activity.

    Do yourself a favor - use stop bath. Stop bath is simply acetic acid (vinegar) the same thing you put on your salad with an oil and vinegar dressing.
    allancobb likes this.
  8. I think that is what happens with normal fixer.
    What I see with rapid fixer is that, even when it isn't so used, that it plates out silver on the inside of the bottle.

    As well as I understand it, that happens when the pH gets too high. If you have a pH meter, and add acetic acid to keep the pH right, it should last longer.
    It might be that normal fixers use more boric acid, where rapid fixers use acetic acid, where the latter is more volatile and so escapes with time.
    (I don't use it quite often enough.)

    With Diafine, an acid stop bath is not recommended, and I might not rinse as well as I could.

    For prints, I normally use an acid stop bath.
  9. Both standard fixer and rapid fixer use acetic acid and boric acid as part of the formula. Standard fixer uses sodium thiosulfate to dissolve the remaining, undeveloped silver halide, whereas rapid fixer (depending upon the formula) will use either ammonium thiosulfate, or sodium thiosulfate with ammonium chloride to dissolve the undeveloped silver halide.
    Last edited: Apr 13, 2017
  10. That's because the developing agents in Diafine cause the emulsion to swell to a greater extent than other developers. When you put the film in the acid stop bath, it causes the gelatin to shrink. With Diafine, this can cause reticulation which makes the emulsion have an alligator pattern from shrinking.

    While the emulsion still shrinks in the fixer, the fixer contains a gelatin hardener that prevents reticulation.
  11. I always thought it was because of the large amount of carbonate in part B.

    Also, it is more usual to use fixer without hardener now.
    I usual use Ilford Rapid Fixer, which doesn't have a hardener.
    For Kodak Rapid Fixer, the hardener is separate.
  12. The carbonate is what makes the gelatin swell. The reason Diafine produces an increase in film speed is that the first solution swells the gelatin allowing more rapid transfer of the developing agents through the gelatin with the carbonate as an accelerator in the second solution. The increased carbonate softens the gelatin further.

    There's a reason you are told to not use an acid stop bath - that reason is the possibility of reticulation from the swollen gelatin shrinking rapidly and pulling apart as in shrinks. If you think there is some other reason, please provide the reason and chemistry behind it.

    I have no idea what's "usual" for you. But, if I were you (and I'm not) I wouldn't project my processing methods as being ubiquitously used by everyone. Why would you purposely leave the hardener out of film fixer?

    Leaving the hardener out of film fixer makes the film more prone to scratching because the gelatin is softer. But, it's your film and you can do whatever you want to with it

    BTW - please provide the formulas for Kodak and Ilford rapid fixer. I'd like to verify that there is no hardener in Ilford fixer.

    I'm simply telling you the chemistry behind how and why things happen. If you don't want to believe me - do your own research. You'll find out I'm telling you simple facts that can be found in a variety photographic technical sources.
    Last edited: Apr 14, 2017

    says that it is non-hardening, and even more, must not be used with hardener.

    I don't use it, but there is a reduced water film wash system for use with non-hardening
    rapid fixers.

    Oh, and when you mix carbonate and acid you get carbon dioxide, something else you don't
    want inside the emulsion.

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