Sodium sulfate

Discussion in 'B&W: Film, Paper, Chemistry' started by Alessandro Serrao, Apr 21, 2009.

  1. Alessandro Serrao

    Alessandro Serrao Member

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    In my everlasting quest to find a universal b&w reversal recipe, I'm just beginning to dig into the use of sodium sulfate in the first developer.

    As far as I know sodium sulfate is used as an anti-swelling agent. Now the rationale for this is: if I use it in the first developer then my emulsion can't swell much and so it receives the least mechanical insult in the following permanganate bleach.

    Now a couple of questions:
    1) what's the amount
    2) how, on a molecular level, sodium sulfate acts as an anti-swelling agent
    3) how does it interfere with the development process (I use Kodak d-19)


    Thanks in advance, I can't wait to know...
     
  2. Christopher Walrath

    Christopher Walrath Member

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    I think I could answer number three, anyhow. I'll leave number two to Ron and number one to others. The emulsion needs to swell somewhat so that the developer can interact with all of the silver and if you prevent the natural swelling that occurs during development you might incur some issues that prevent the developer acting evenly across your negs.
     
  3. panastasia

    panastasia Member

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    A most interesting inquiry! I too, would like to know what to do with the 1 lb jar of sodium sulfate I have (bought by mistake and didn't return). B&W reversal sounds interesting.
    I'm also waiting to learn..
     
  4. Photo Engineer

    Photo Engineer Subscriber

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    It is normally used at about 25 - 100 g/liter depending on developer. The reason is that it isn't all that soluable in the presence of the rest of the ingredients. It will slow developing action by a small amount to a great deal depending on gelatin level and amount used. It can also decrease contrast.

    It works somewhat like ordinary table salt used in drying meats. In fact, if sodium sulfate didn't taste so bad, I suppose it would be used to cure and dry meats. It tends to shrink or dry proteins and cause strands of protein to shrivel up and pull closely together. It acts sort of like squeezing a sponge when you dip it into water, but by chemical means.

    PE
     
  5. Alessandro Serrao

    Alessandro Serrao Member

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    My first tought is that being a salt it disrupts the solvation shells around the NH3+ and COO- termini of proteins, displacing the H2O molecules thus limiting the water induced swelling of the gelatine.
     
  6. Photo Engineer

    Photo Engineer Subscriber

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    Well, it can break hydrogen bonding then. :D

    There is more to it than that though and we do not have a good understanding of the process.

    You have to remember that a fair fraction of the amines are consumed by the hardener though so that is not all that is taking place. When the hardener "deactivates" two amine sites by cross linking them, what you describe is no longer an option. In fact, from one POV my first sentence is incorrect in that the gelatin coils more tightly as if hydroen bonding has increased. But, if that were simply the answer, it would increase with water as well as with the carboxyl groups.

    The answer is not simple, and I'm not sure I can give you one. I can say that all sulfates behave the same and some are used as hardeners such as Alum and Zircotan, but they only work in acid solution. Sodium Sulfate does not harden and usually works best in alkali. Hmmm, I seem to remember a use of Zircotan in alkali. I have no way to check it out, but it may work in both acid and alkali.

    Many of these salts were used in the "Niter" used in Egypt to dessicate bodies for mummification. This is a different process in that you start with dry salts rather than the wet salts we are talking about. However, just as with NaCl mentioned above, they can be used dry or wet depending on the amount of "pickle" effect you wish to achieve.

    PE