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Thread: PMK Pyro shelf life

  1. #1

    Join Date
    Mar 2000
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    PMK Pyro shelf life

    I bought a bunch of PMK Pyro developer from B&S some time ago and didn't use as much as quickly as I thought. This is the stuff that comes as one bottle of Solution A and one bottle of Solution B. The company recommends a shelf life of 6-12 months but I wonder whether it is common practice to throw away these undiluted solutions after that time. Practically speaking, do you throw the stuff away after 6-12 months?
    Thanks
    Tom Keenan

  2. #2
    Drew Wiley
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    Re: PMK Pyro shelf life

    As long as the solutions are kept separate, PMK has outstanding shelf life. But a year is
    a long time. Might be fine, but I'd test it before developing any important negatives.

  3. #3
    Eric Woodbury
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    Dec 2003
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    Re: PMK Pyro shelf life

    My solution A lasts forever. I'm sure the bottle I have now is a year old. My B solution, even though I make it at half strength, seems to develop crystals in the bottle and therefore changing the mix. So now, I measure and add dry-weight part-B to the developer when I mix it up.

    I believe Gordon mentions in his book that he mixes his part A up well in advance and that it keeps a good long time.

    Still a good idea to run a test.
    my picture blog
    ejwoodbury.blogspot.com

  4. #4

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    Re: PMK Pyro shelf life

    Tom,

    I just tossed about one-quarter of a bottle of solution A of PMK pyro. It had turned very dark brown. I tested it on some negatives and it was still active (the negs look good), but I was not sure if it was as active as it was new, so didn't want to take the chance. I may have been able to use it for awhile still. I had had the partially-full quarter-liter bottle in my Vienna darkroom (which got relatively little use these last few years due to doctoral work in the states) for almost seven years.

    If your solution A is still a nice straw yellow, it is in great shape still. As for solution B, the sodium metaborate is very concentrated in this part and often precipitates out. Shake the bottle well before using and let the mixed PMK stand for a few minutes (but not too long!) to make sure any particulate metaborate has dissolved before using. It should be fine. My seven-year-old solution B is still fine, though it too has some crystals in the liquid.

    Hope this helps,

    Doremus Scudder

  5. #5
    Greg Greg Blank's Avatar
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    Re: PMK Pyro shelf life

    I second the notion that solution A lasts forever. I formulate my own PMK, and have done so since about 1996. I buy the raw components... I get some of the components from the grocery store to make solution B "Metaborate"....it's cheap enough you could in theory discard it after a month. But being the cheap son of gun I am I merely swish the Metaborate around in the "Plastic" bottle to reconstitute the crystals.....and I visually determine how much B, I should add based on the apparent density related to experience and the ratio I establish when it is fresh. Maybe not so scientific but close enough for government work



    Quote Originally Posted by Tom Keenan View Post
    I bought a bunch of PMK Pyro developer from B&S some time ago and didn't use as much as quickly as I thought. This is the stuff that comes as one bottle of Solution A and one bottle of Solution B. The company recommends a shelf life of 6-12 months but I wonder whether it is common practice to throw away these undiluted solutions after that time. Practically speaking, do you throw the stuff away after 6-12 months?
    Thanks
    Tom Keenan

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