Anti-halation question

Discussion in 'Black and White' started by trooper, Aug 3, 2003.

  1. Something I've never seen a direct comment on and I've wondered about:
    When I prewet with wetted water, I always get a dark color in the
    water when I pour it off prior to replacing with developer. When I
    use developer first and no pre-wetting, I dont seem to see this. I
    would expect the color to show up somewhere along the trail from
    developer to hypo eliminator but it doesn't, at least with the
    chemistry I use. What is happening, chemically, that causes this
    behavior? What is the anti-halation layer comprised of? Does the
    alkalinity of the developer simply consume it?
     
  2. Craig, if you use the words "purple," "purplish," "blue" or variations, or "tint," "tinge" or other terms you'll find several fairly recent threads discussion this issue.

    However, it's debatable whether the color that's poured off is from the anti-halation dye or emulsion dyes that make up part of the light sensitive layer. I've read reports indicating that it may be one or the other or even both, but nothing definitive from Kodak's website. I mentioned Kodak specifically because it's the T-Max films that seem to prompt most of these discussions.

    I don't presoak film, haven't since I used sheet film 30 years ago in school, so I can't comment on any color that comes off during that step.

    However I have seen discoloration, sometimes mild, sometimes striking, come off with most developers. Rodinal produces by far the most striking color change, becoming bright purple when poured out after developing TMY. Microphen becomes gradually discolored, something I noticed when reusing the undiluted stock solution with TMY. And my batch of Diafine has become quite dark, about like weak tea, from repeated use with Tri-X, old and new emulsions.

    ID-11 and Ilfosol-S don't seem to strip off these dyes and most of the color comes off during fixing and washing. When I wash TMY after developing in Microphen or Rodinal and fixing normally very little color comes off in the wash water. But when I process the same film in ID-11 or Ilfosol-S most of the color comes off in the wash water, and it takes some assertive agitation with in-tank washing to get the film base as clear as possible - tho' some slight tint remains.

    If I'm remembering correctly Pete Andrews was the fellow who speculated last year that the pH of our water can influence this effect. I know the pH of our water tends to be alkaline because it's well water from a limestone basin. I see differences throughout the month in the clarity of my film bases which I attribute to the varying level of salt in our water softener, which I don't maintain regularly enough.

    As for the components of the anti-halation layer, I couldn't find any specific answer to that while recently researching Kodak's site.
     
  3. Some AH dyes wash out either in the pre-soak or the dev. Some bleach in the dev and some bleach in the fix, hence you don't see them. It varies according to the manufacturer.
     

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