Brian Ellis (beellis@gte.net)
Fri, 22 Oct 1999 22:37:52 -0400
The anti-halation dye is discussed in Phil Davis' book "Beyond the Zone System,"
now in its fourth edition, if anyone cares to look. When the BTZS tubes that Phil
designed are used, this dye is removed or eliminated or uncolored or whatever you
want to call it after a minute or so in the fix. The extent of the anti-halation
dye "problem" seems to depend to some extent on the local water quality. Phil,
who lives in Michigan, seems to have some problems with it and that's why he goes
on at some length about it in his book. Many participants in the two of his
workshops that I've attended have reported little or no problem with it so we've
speculated that the severity of it may be a function of the local water.
Richard Knoppow wrote:
> At 04:31 PM 10/22/1999 -0600, you wrote:
> >On Fri, 22 Oct 1999, Richard Knoppow wrote:
> >
> >> Actually the backing is not removed, only decolorized. In think the only
> >> backing which is physically removed is the Rem-Jet baking on some Kodak
> >> motion picture color films and on Kodachrome. You can experiment with a
> >> scrap of film. You will find that either developer or fixer will decolorize
> >> the anti-halation layer but that nothing is removed from the film.
> >> In some cases a plain water soak will decolorize it.
> >> Some color films have an anti-halation layer under the emulsion.
> >
> >I have a sneaking suspicion that we are getting close to discussing
> >semantics here. At any rate, the color from the antihalation
> >coating needs to be removed. My impression is that this is basically a
> >water soluble dye that is washed out of either a layer in the emulsion or
> >a coating on the back of the film. Indeed when I'm developing film my
> >prewash water and developer tend to become discolored with this dye that
> >evidently is removed from the film. Whether or not this means that the
> >substrate carrying the dye is removed I don't know.
> >
> >What I'm curious about, is whether or not the film processing causes the
> >dye to become less soluble, or if somehow the developer contains something
> >that removes, washes, or decolorizes this dye better?
> >
> >Another way of formulating the question would be to ask: what is the
> >mechanism for the decolorization you talk about?
> >
> >- Wayde
> > (wallen@boulder.nist.gov)
> >
> Well, I think it is a bit more than semantics. The anti-halation dye is
> in a coating of gelatin on the back of the film for most films. It is
> sometimes in a coating near the substrate in some color films. The gelatin
> is not removed, the dye is either decolorized or washed out, I don't know
> which. Its known that some dyes are destroyed by acids and others by
> alkaline solutions. That may or may not be what is happening here.
> I've found that both developer and fixer will decolorize it. Developer
> seems to be much more effective. I tried a solution of sodium carbonate
> just now. It worked but was slow. Dektol stock removed the color in a few
> seconds. A fairly strong solution of Acetic Acid did not work nor did plain
> water and a ten minute soak. Hypo works, but slower than developer and can
> leave just a bit of residual color.
> I can't cite any literature at this point but will do some reading.
> In any case, the reason for making the distinction is that actually
> removing a coating wouild require a fair amount of agitation rather than
> just exposure to the chemicals.
> You can prove the coating is still on the back by gently scraping it off.
> Before processing it comes off along with the color. After processing it
> comes off clear. The coating is also an anti-curling coating.
> ----
> Richard Knoppow
> Los Angeles,Ca.
> dickburk@ix.netcom.com
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