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  1. #11
    Ian Grant's Avatar
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    Potassium Metabisuphite is also used in some powder developers as a preservative to help prevent oxidation of the developing agent(s) in the packaging, some contain no carbonate but if they did that was packaged as Part B separately.

    So you had a situation where the powdered form of a developer contained Metabisulphite but the liquid form didn't.

    Ian

  2. #12
    David Lyga's Avatar
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    Gerald Koch: I must confess something that I thought too trivial or even esoteric. Your quote about Geoffrey Crawley: "small amount of bicarbonate that was necessary for the developer to work correctly"...

    Is anyone able to corroborate or clarify the following? Sometimes I add carbonate to the developer and find that I added to much. I 'rectify' by adding some baking soda in order to bring the energy back down. Honestly, the developer seems to act smoother and impart tones more evenly. I even explored this further by dipping a bit of film or paper into two small cups of developer in roomlight: one with the bicarbonate and one without. The one with the bicarbonate, although slower to develop, seems to develop more evenly from the start and, although both examples were even with full development, I like the initial evenness that I thought was brought about by the bicarbonate. Perhaps this is simply conjecture and wishful thinking on my part but I wonder if there is any agreement with this. In my unscientific way of thinking, it seems to be a sort of buffer. Thank you. - David Lyga

  3. #13

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    You all got me curious, so I did a search for the uses of bisulfite and bicarbonate in developers. My collection is not as big as Ian Grant's, but it is pretty good. In almost all cases, the only purpose is to control pH. Bisulfite is particularly used in pyro stock solutions to keep the pyro acid. It is also used to lower the pH in many fine grain developers. It occurs in many litho developers, where it is sometimes used with paraformaldehyde to produce a developing agent. Some stranger applications of bisulfite also show up, however. The most notable is in Rodinal type developers, where its pH control possibilities should be overwhelmed by the hydroxide. It also shows up in a lot of photofinishing developers, where it is used with carbonate and bromide. The probable design use in that case is to stabilize the pH. Some paper developers use bisulfite when additional warmth is needed.

    Bicarbonate is rare. It is usually used as either a very low pH alkali or with carbonate as a buffer. FX55 is a curious variation. It contains both bisulfite and bicarbonate with carbonate. That would be a very strange buffer, so Crawley must have had something else in mind.

  4. #14
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    Well, as pH goes up, fog and contrast go up as does development rate. As pH goes down, these things also go down. Bicarb lowers pH.

    Bicarbonate is NOT a classic antifoggant.

    Antifoggants fall into 2 classes, organic (benzotriazole, PMT and etc) and inorganic (NaBr). They all work by about the same mechanism, that is, they adsorb to the grain surface thus reducing the exposed silver on the grain surface, and/or they reduce the available silver ion concentration in the developer. Simply said, they can form salts with silver!

    All of these effects are stronger on Chloride emulsions, less so on Cl/Br emulsions, and even less so on Br/I emulsions.

    PE

  5. #15
    David Lyga's Avatar
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    Thank you for the clarification PE. I will have to test again, but it did seem to help some.

    However, nworth, something persists in me to believe that there is some advantage with the combination of both carbonate and bicarbonate, although they cancel each other out, Ph-wise. Maybe this is plain wrong but I wanted to present this possibility regarding evenness of development. - David Lyga

  6. #16
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    David, something is going on. Try measuring the pH if you can.

    PE

  7. #17
    Ian Grant's Avatar
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    David, your 10-20g/litre in a working solution is going to have a powerful Buffering effect, you could expect a drop in pH of around -1 (so maybe pH 11 to pH10.

    This will drop the developer activity quite significantly. Many people over devlop their B&W papers anyway so this may be why you're seeing a differance.

    Ian

  8. #18
    David Lyga's Avatar
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    Well, both Ian and PE: I fully know that there is a considerable change in activity with that much baking soda or carbonate. I do not have (is it litmus paper?) or other material to specifically measure the pH but there is, of course, considerable activity change with either. Maybe it is simply my false perception here with evenness, but I did (many times this) put two pieces of film, vertically, into two developers, one normal and the other with both carb and baking soda (enough to even out the activity back to normal) and I have to say that the initial evenness of the carb & soda was considerably better. Of course, at the end of development I think that this mattered little. But it was, for me, interesting. (I keep trying to find out things that Kodak 'forgot' to explore when I do these crazy things!) Besides there really are advantages to the baking soda that the 'literature' rarely mentions. Slowing down activity without resorting to either dilution or colder temperature is surely worth mentioning.

    Folks, always take with a grain of salt my 'finds': I am not a chemist or one who even has a profound theoretical base for these assessments, but, nevertheless, they might be interesting to consider. - David lyga

  9. #19
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    David, get pH paper at some chemical supply house. It runs about $25 for about 100 strips. My tube has lasted several years. One strip, one test.

    PE

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