Film Base Permeability

Discussion in 'Darkroom Developing and Printing' started by Ken Smith, Apr 29, 2004.

  1. Ken Smith

    Ken Smith Guest

    Does film base need to receive chemistry when processing?
    Could it conceivably remain flat and dry while chemicals act on the
    emulsion?
    Is it at all permeable, and does it need as adequate a washing as the
    emulsion?

    I ask because I'm experimenting with a method that developes two films
    at once lengthwise in a long tray, base to base.

    While I can be attentive to seperate the films during agitation in
    chemistry, I'm wondering how concerned I should be about wash water
    flow to the base in a final; no wash aid because of pyro, 15-20 min
    wash.
     
    Ken Smith, Apr 29, 2004
    #1
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  2. There shouldn't be any problem; spooling two films back to back has
    been, at times and for some people, a standard method of getting two 120
    films into a single 120 tank to obtain economy of chemical usage that
    matches 35 mm. I've even heard of it being done with 35 mm.

    The film base has a gelatin "anti-curl" coating, but with most films
    there's nothing coated onto or in that gelatin; antihalation layers are
    under or in the emulsion, on the emulsion side (they have to be, in
    order to protect from reflections and light piping inside the base), and
    the base coloration is in the plastic material of the base itself, not
    coated on. Worst case, if you find a particular emulsion gives trouble
    that way, you can rewash the film and will most likely remove any dyes
    that might be present in the anti-curl coating. However, be certain you
    separate the films for drying; the anti-curl coating is thin, but more
    than sufficient to glue two strips together, back to back, for eternity.

    The possibility of fixer remaining in the anti-curl coat is a concern,
    however, with or without wash aid; it would probably be preferable to
    separate the films for washing. Worthy of note here; if you use an
    alkaline fixer like TF-4, washing can be as little as five minutes for
    archival removal of fixer (though longer wash may still be preferred to
    promote stain formation); that's not too long to spend periodically
    separating the films for flow between, since you'll probably spend twice
    that long just in the developer.

    --
    I may be a scwewy wabbit, but I'm not going to Alcatwaz!
    -- E. J. Fudd, 1954

    Donald Qualls, aka The Silent Observer
    Lathe Building Pages http://silent1.home.netcom.com/HomebuiltLathe.htm
    Speedway 7x12 Lathe Pages http://silent1.home.netcom.com/my7x12.htm

    Opinions expressed are my own -- take them for what they're worth
    and don't expect them to be perfect.
     
    Donald Qualls, Apr 30, 2004
    #2
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  3. Ken Smith

    Ken Smith Guest

    Excellent answer, Thanks.
     
    Ken Smith, Apr 30, 2004
    #3
  4. Ken Smith

    Dan Quinn Guest

    They do glue well too! Now I know why. I never thought to ask and
    in all my post reading I never once read an explanation. Dan
     
    Dan Quinn, Apr 30, 2004
    #4
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