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  1. #11

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    Quote Originally Posted by Nicholas Lindan View Post
    The flow patterns are due to very small thermal gradients - fractions of a degree, the sort of thing you can't get rid off - that set up small convection cells. The surface of the developer will be cooler due to evaporation, as the water cools it becomes denser and falls to the bottom of the tray where it displaces warmer developer that rises to the top. There will be additional gradients due to the developing process as the developing agent is oxidized and halides are given off resulting in small changes in developer density.

    You will only see these patterns when the developer is standing quite still with no agitation.
    Thanks Nicholas, I would have never thought of that explanation. I'll chalk it up to a learning experience but am confused why my foma 100 doesn't do a similar thing with stand development?
    regards
    Erik

  2. #12
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Erik L View Post
    confused why my foma 100 doesn't do a similar thing with stand development?
    That's the real question - some possibilities:

    • More developer per unit of film area
    • Greater developer depth
    • Less temperature difference developer to air
    • Less temperature difference bench/sink/tray to developer
    • Less bromide in Foma emulsion
    • 8x10 Vs 11x14 film size

    It may be that the conditions that exhibited the problem were unique with just the right temperature gradients and a second film developed with the same stand regime would not exhibit the same problem.

    It is a bit like being hit by lightning while playing golf in a thunderstorm: it is to be expected; but playing golf in a thunderstorm is no guarantee of getting hit. The 'gator skin' effect is to be expected, but there is no guarantee of it happening.

    And of course, there is no guarantee of the convection cell theory being correct - the problem could be due to something completely different such as a film manufacturing defect.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  3. #13
    Alex Bishop-Thorpe's Avatar
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    Most interesting case of darkroom detective I've read in some time, well done guys.
    The Analogue Laboratory, or 'so you built a darkroom in an old factory in the industrial zone'.
    Blog thing!.

    Worry less. Photograph more.

  4. #14

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    Nicholas, thanks for thinking this through. I liked your original theory whether it's true or not
    regards
    erik

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