"Geoffrey S. Mendelson" wrote in message
...
Joe wrote:

But the Edwal, as I remember it, is testing for whatever
silver
reduction ability remains. Does not the fix go bad for
other reasons
that simply reaching it's capacity? I never even approach
capacity....

It never did when I was developing film. Fixers are acid
and therefore do not
mold or turn rancid. They do decompose slighlty so you
find a percipitate
at the bottom of the bottle and some of it sticks.

What I used to do was keep a box of cheap coffee filters
in the darkroom
and when I wanted to develop something, I put one in a
funnel, stuck the
funnel in a graduated cylinder (or a bottle), shook the
fixer well to dislodge
anything on the bottom and filtered it before use.

I doubt that you have to do it with paper,you could just
let any sediment
stay in the bottle, but I would not do it with film
because I would
(probably unjustifiably) that something would stick to the
film and not
be removed in the wash.

Geoff.

Edwal fixer checker is a solution of potassium iodide.
When there is more than a certain amount of silver complex
in the fixer it is caused to precipitate as a white cloud.
If the cloud goes back into solution in a second of two the
fixer is supposed to be OK but if its permanent the fixer
should be tossed. The problem is that the amount of
residual silver that can be in fixer that tests good is too
much.

Also, with time fixer begins to sulfurize. That is the
sodium thiosulfate begins to decompose. The acid in acid
fixer is the primary cause of this decomposition. The sodium
sulfite in the fixer help to protect the thiosulfate from
the acid but also performs other duties. Kodak gave the life
of standard fixer as about 2 months. I would not stretch it
for much more. I don't think Edwal Hypo-Check will test for
partially decomposed fixer. However, usually you can smell
it because there is usually an odor of sulfur dioxide (sharp
smell) and often hydrogen sulfide (rotten eggs). Also,
decomposing hypo tends to be cloudy and some times has a
white or yellowish precipitate in the container. This is
also true for "rapid" or ammonium thiosulfate fixers.
If you work rarely its a good precaution to mix the hypo
fresh each time.
The best test of a fixer is to fix out a sample of paper
or film and treat it in sodium sulfide (not sulfite) tester.
A drop or two is placed on a clear area of the film or a
white area of the print and allowed to stand a couple of
minutes, then rinse off. If the material is completely fixed
there will be no stain. The sulfide tones silver halide as
readily as metallic silver so will show up anything left by
the fixer. The formulas for fixer tester, residual silver
tester, and residual hypo tester can all be found in any
edition of the _Kodak Black-and-White Darkroom Dataguide_
This is no longer published by Kodak but I think should not
be too difficult to obtain used.


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Richard Knoppow
Los Angeles
WB6KBL