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  1. #251

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    Quote Originally Posted by Rudeofus View Post
    And make sure you properly account for bound water molecules when comparing sodium and potassium sulfite. IIRC both come with varying amounts of water per molar unit, make sure you know which one you have in front of you.
    Will do, and thanks for the heads-up.

    Another chemistry question: What would be a good acid to mix into TEA to adjust pH and provide decent buffering?

    I'm thinking of using only TEA (and no PG) as the carrier for the concentrate, about 22 ml of it per liter of developer. That'll push the pH too high even with the ascorbic acid in it, so another stronger acid is needed to pull it down. I'm hoping that 22 ml of TEA plus an acid to convert some TEA into its conjugate acid (pKa=7.8) will provide sufficient buffering to hold the pH at 8.2 or so. The question is: which acid?

    Thanks,

    Mark Overton

  2. #252
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    Here's a list of acids or acidic substances I have found in b&w developers which I think do not act as development or chelating agent: boric acid, sodium metabisulfite, salicylic acid.
    Salicylic acid is soluble in organic solvents so this could be perfect for your recipe. Ryuji uses it in his DS-12 formulation!

    Thanks, Mark, for your great efforts! Based on your thread here I have just ordered a bunch of raw chems and will be ready to try out some stuff in the near future. Right now I'm a little bit worried about heating TEA in my flat with two small children around (they have sustained 4 years of E6/C41 so far :P) but I have access to a dark room once a week so we'll see how far I get.
    Trying to be the best of whatever I am, even if what I am is no good.

  3. #253

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    Mark,
    Xtol contains~0.2g/L dimezone S (phenidone derivative),sulfite @ 85 g/L is a good solvent.
    PC-TEA 1:100 contains 0.025g/L phenidone, sulfite @50g/L was not a good solvent in my test at pH ~8:
    http://www.apug.org/forums/forum37/3...a-sulfite.html
    If my result was right, the sovent effect depends on the concentration of phenidone-ascorbate in the working solution as well as the sulfite.
    It looks like your concentrate, when decided upon, after dilution will give a phenidone concentration beween the two quoted above.
    I hope you get a good solvent effect if a fine grain is the wanted result.

  4. #254

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    Quote Originally Posted by Rudeofus View Post
    Here's a list of acids or acidic substances I have found in b&w developers which I think do not act as development or chelating agent: boric acid, sodium metabisulfite, salicylic acid.
    Salicylic acid is soluble in organic solvents so this could be perfect for your recipe. Ryuji uses it in his DS-12 formulation!

    Thanks, Mark, for your great efforts! Based on your thread here I have just ordered a bunch of raw chems and will be ready to try out some stuff in the near future. Right now I'm a little bit worried about heating TEA in my flat with two small children around (they have sustained 4 years of E6/C41 so far :P) but I have access to a dark room once a week so we'll see how far I get.
    There are lots of acids that can be used. Malic acid, citric acid, gluconic acid, phosphoric acid, sulfamic acid, sulfuric acid, etc. However, the idea of using triethanolamine as the carrier solvent is probably unwise for practical reasons.

    Also, many of the acids above have interaction with iron, potentially useful but potentially harmful. Also, technical grade of those acids may contain a significant amount of iron as impurities. I'd be careful in choosing ingredients.

    If anyone wants salicylic acid, I have a LOT of them and don't plan to use much more of them, so I'd be happy to unload some. Email me directly.

  5. #255
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    What about EDTA? It's acidic and used in color chems to remove iron introduced by impure Na2SO3.
    Trying to be the best of whatever I am, even if what I am is no good.

  6. #256

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    I've discussed EDTA, NTA and DTPA many times in the past. There are reasons why I don't use them.

  7. #257
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    In B&W developers, the Dequest series of chelating agents are better wrt Iron.

    PE

  8. #258
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    PE, Mark was looking for acids which don't interfere with the other parts of his developer other than lowering pH. The dequest products you suggested seem to be alkaline to my highly untrained eye. The combination of phosphonates you suggested and one of the acids Ryuji suggested might do the trick, though, lowering the pH and taking care of iron.
    Trying to be the best of whatever I am, even if what I am is no good.

  9. #259
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    I have used Dequests that were in the free acid form and had very low pH. I could therefore adjust the pH to any value I wished.

    PE

  10. #260
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    Are these Dequests substances a normal person outside a lab would have access to? As far as I have understood this, Mark is no chemist, neither am I, and neither one of us has access to "special stuff". I didn't even get (NH4)2 FeIII EDTA here . Marks and my approach to mixing devs seems very different from yours and Ryujis ....
    Trying to be the best of whatever I am, even if what I am is no good.



 

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