Crystallising Potassium Oxalate

Discussion in 'Alternative Processes' started by Ian Leake, Feb 15, 2013.

  1. Ian Leake

    Ian Leake Subscriber

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    I use hot Potassium Oxalate for developing my platinum and platinum/palladium prints. I've noticed that when the developer cools it tends to form crystals in the bottom of the jug or bottle. Sometimes the crystals dissolve when I heat them gently, but not always. I'd like to stop them forming.

    Does anyone have any experience of this? If so, how do you deal with them?

    Thanks in advance.
     
  2. Vaughn

    Vaughn Subscriber

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    You probably are having water evaporate from the developer and thus concentrating it and forming a super-saturated solution. You might try adding some distilled water after your printing session to bring the concentration down.

    What I have done is pour the Potassium oxalate into my warming-container, leaving the crystals behind. Then add the distilled water to the crystals, warm it up and when they are dissolved, pour it in with the rest of the developer.
     
  3. Gerald C Koch

    Gerald C Koch Member

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    It's hard to make any conclusions about the problem without the specific strength of the solution and your darkroom temperature. The solubility of potassium oxalate is 31.0 g/l at 10C, 36.4 at 20C and 38.9 at 30C. As an example, if your working solution contains more thaqn 38.9 g/l and cools below 20C you will see some crystalization.
     
  4. Ian Leake

    Ian Leake Subscriber

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    Thanks Vaughn and Gerald, I think you've solved my problem (well, it's not really a problem – it's more of an oddity really).

    I make up 33% a Potassium Oxalate solution as standard. Certainly some evaporates while I'm working, although not that much because I keep it in a cafetière which tends to recycle the evaporated water. But my darkroom gets cold at night. I'm not sure how low the temperature gets, but sometimes it's probably below 10°C.

    I guess I could eliminate the crystallisation by using a weaker solution, but I'm not sure that I want to do that. So I need to either live with it or keep my developer warm at night.

    Thanks again,

    Ian.