wrote in message
ps.com...
RE

... i'm wondering if i could just double the
fixing time and use the 1+9 instead of the 1+4 (as the
'strength'
of the 1+9 should be half that of the 1+4). would that
work?


If that were the case a 1:24 dilution, 1/5 film
strength, would
take 40 minutes; allowing for 8 minutes at 1:4. Such is
not the
case. I expect 8 to 10 minutes at 1:24. Exceptional films
might
take a little less or more. Conditions: 20ml of fresh A.
Thio.
concentrate in a solution volume of 500ml; agitation 1st
minute continuous and 15 seconds each there after.
One-shot use. Dan

A lot of chemical processes are not linear, for instance,
developer diluted to half strength does not take twice the
time to develop. However, the danger with highly diluted
fixer is that there may not be enough free thiosulfate ions
to complete the fixing process. The only way to tell is to
test for residual silver. The simplest test is to use a
dilute solution of Sodium Sulfide. Kodak also used to
recmmend Kodak Rapid Selenium Toner diluted 1 part to 9
parts water. However, this test will fail unless the film or
paper is well washed. Completely fixed film or paper should
not show any detectable stain from either test.
A clearing time test is useful for checking the condition
of a fixing bath. The old rule of thumb is that it takes
about double the clearing time for complete fixing. This
assumes the fixer is fresh enough to complete the fixing
process, which is progressive. If its not the emulsion will
not fix out completely in any length of time.
Clearing time tests should be done with a sample of the
film being fixed. The film should be soaked in water for a
few minutes since wetted emulsion fixes at a different rate
than dry film.
For archival purposes a two bath system is strongly
recommended. Its also more economical because the capacity
is from 4 to 10 times that of a single bath.
The use of a Sulfite wash aid will also increase
effective capacity because it releases some partially fixed
halide which would otherwise remain tightly bound to the
emulsion.


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Richard Knoppow
Los Angeles, CA, USA