From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 12/14/02-03:27:08 AM Z
----- Original Message -----
From: "Jeff Buck" <jeffbuck@swcp.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, December 13, 2002 4:30 PM
Subject: Ammonium Thiosulfate "Rapid" Fix
> This is an addendum to the brief discussion the other day
about the
> possible use of ammonium thiosulfate "rapid" fix for alt,
and is by way of
> a cautionary note for those of us, and I think there are
many, who fix our
> film w/ ammonium-based fix... In the Film Developing
Cookbook, Anchell
> gives this very simple recipe for an ammonium rapid fix --
800ml of 57%-60%
> ammonium thiosulfate + 60g of sodium sulfite + 5g sodium
metaborate and
> water to make a liter = stock. Dilute 1:4 for working.
Anchell says to
> fix for three times clearing or 3-5 minutes. When the
clearing time has
> doubled w/ use of the fix, discard. I found much shorter
clearing times,
> 1-2 minutes, applying the 3X test. I'd take a strip of
exposed film, pop
> it in the fix, and it would clear in 20" (fresh working
solution). There
> are warnings in Anchell and elsewhere, of course, re:
over-fixing. I was
> bugged by this discrepancy, however, and ran it by a
couple real
> experienced sheet film people who said, "Kick back; your
numbers are right
> on." I don't think so. At some point, a sheet film guy
suggested that my
> test strips might not be as "clear" as I think, and
suggested this
> procedure: Before popping the strip of exposed film in
the tray of fix,
> place a single drop of fix in the middle of the strip and
leave it there
> for way long, several minutes, while you do something
else. Then take the
> strip with the now real real clear "hole" in the middle
and pop it in the
> tray of fix. You will know the strip is REALLY clear when
you can no
> longer discern the "hole". With fresh fix, this takes
about one
> minute. Times 3 is the low end of Anchell's "3-5
minutes". -JB
Virtually any fixer formula can be converted to a "rapid
fixer" for substuting ammonium thiosulfate for sodium
thiosulfate _anhydrous_. This is about 67% of the amount
given for crystaline hypo.
As with any fixer the clearing time indicates when the
emulsion is essentially fixed. Double this time is allowed
to insure the solublization of all the silver halide,
especially when the fixer is somewhat exhausted.
If a single fixing bath is allowed to become exhausted
beyond a certain point it will still clear film but will not
completely fix it no matter how long the fixing time is
extended. Fixing is a chain of reactions which convert the
insoluble silver halide to a water soluble form which
diffuses out into the fixing bath and wash water.
A better plan than extended fixing time is to use a two
bath system. The second bath stays fresh enough, i.e., has
enough thiosulfate ions free in it, to complete the fixing
process. If unfixed fixer reaction products are left in an
emulsion they will change over about a two week period into
a form which can no longer be made soluble by re-fixing.
Given time, these products will begin to decompose staining
and attacking the image. The best test of fixing is a test
solution of sodium sulfide or Kodak Rapid Selenium Toner. If
the test solution generates a stain it indicates there is
some halide or silver complex left.
The stain left in Tri-X and T-Max may be the result of
insufficent fixing. However, I've found that extending the
fixing time in reasonably fresh fixer does not remove the
stain from T-Max. Sulfite wash aid removes it immediately,
however sulfite wash aid also removes some otherwise
insoluble silver complex, so, its success may still indicate
incomplete fixing.
Films like T-Max and Tri-X contain a lot of silver iodide.
The Iodide tends to slow down fixer action. Ammonium
thiosulfate (rapid) fixer is less sensitive to iodide than
sodium thiosulfate fixer, so it has some advantage with
these films. In a two bath system the bulk of the silver
complexes, including the iodide, comes out in the first
bath, so the difference in capacity between ammonium and
sodium fixers is less when two baths are used.
The minimum fixing time for Tri-X or T-Max in reasonably
fresh two bath fixers is about ten minutes total (both
baths). A treatment in Kodak Hypo Clearing Agent before
washing should leave both films clear.
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