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  1. #11

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    I ran across this a while back, but I was (and am) still learning, so I'm not sure how to use this in my fledgling emulsion recipe. It appears that Kodak tried to add the formate at the end of the proccess, and that it was only effective at higher pBr (which I must assume is the negative log of the concentration of bromine ions?)

    See
    http://www.freepatentsonline.com/EP1271233.html

  2. #12
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    Kodak measures pAg or vAg as it is more accurate, and is more indicative of the actual conditions.

    In any case, this method did not work out well and was abandoned AFAIK. Kodak uses an Osmate complelx.

    PE

  3. #13

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    This would be just the thing for astro-photography. I currently bake the tech-pan film in a hydrogen atmosphere for 2 days to limit reciprocity failure. Even an emulsion which only lasted a few days would be useful as you would coat plates just prior to use. It sounds like this formate emulsion would be competitive with CCD technology, but much cheaper and MUCH higher resolution.

    Regards - Jim Browning

  4. #14
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    There is a French patent on this that was leased to Agfa by the inventors. It was intended to improve speed IIRC. Jon Eikenberry, the inventor, was a respected Kodak Engineer and did fine emulsion work, but I don't remember if this was ever adopted. All I can say is - try it.

    PE

  5. #15

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    Kodak measures pAg or vAg as it is more accurate, and is more indicative of the actual conditions
    How do I measure pAg? I would like to be able to do that.

  6. #16
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    It is generally measured using a conductivity meter and silver or silver halide plated electrodes. A normal junction cannot be used because the chemistry involved affects the emulsion adversely. You have to calibrate the meter in pAg units as the result is expressed in mV. That is why we use vAg as it is a direct and more accurate measure.

    The vAg scale goes from about -250 mV to about + 200 mV.

    PE

  7. #17

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    Quote Originally Posted by Photo Engineer View Post
    It is generally measured using a conductivity meter and silver or silver halide plated electrodes.
    A conductivity meter does not work for this.

    You need a pH meter.

    A silver ion specific electrode is the other item needed. You can do with with:
    • one silver ion electrode half cell and
    • one reference electrode

    or
    • one combination silver electrod which has both the silver ion electrode with a reference electrode in one physical package.


    As far as electrode go, they will generally be expensive, and you need to maintain them well to keep them functional.

    You can buy a used digital pH meter for not a lot if you are lucky, but I would not buy a used silver ion electrode unless it was really cheap and then I would expect that it would not work... Now a silver ion electrode is pretty spendy - $500 or so.

  8. #18
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    Kirk;

    We used to measure pH with a conductivity meter. In fact, we used to use a Wheatstone bridge. Yes, I'm that old. It works. And the method you describe might work, but the electrodes are critical to avoid poisoning the emulsion.

    When you get down to it, a pH meter is really a tricked up conductivity meter with a pair of fancy electrodes.

    PE

  9. #19

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    Well when you break it down that way, sure. but if someone is to go and buy a conductivity meter and a silver electrode, they will be disappointed as they will not work together.

  10. #20
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    Well, I am working on a method that uses a VOM and Silver electrode with a friend. We are trying to devise an inexpensive method. And a VOM can be used as a conductivity meter too.

    The biggest problem is not building a meter setup, it is the calculations involved in calibrating it. Someday I may publish a table on this. It is incredibly complex.

    PE

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