[pure-silver] Re: PMK and MCS
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sun, 30 Apr 2006 21:31:08 -0400 (EDT)
From: john stockdale <j.sto@xxxxxxxxxxx>
Subject: [pure-silver] Re: PMK and MCS
Date: Mon, 01 May 2006 07:47:04 +1000
> Ryuji, is that because the sodium thiosulphate fixer takes longer to fix
> thereby soaking more into the fibre base, or does the ammonium thiosulphate
> just wash out faster?
>
> I note that you have specified "at the same pH".
Both. The magnitude of difference varies depending on the condition,
but the latter alone is often making enough difference, if you read
Green and Levenson's report. They used one-sided x-ray film for their
testing, and so the former factor was absent.
Ammonium thiosulfate fixers fix the emulsion faster, so if you fix the
material for a predetermined fixing time, rapid fix goes farther
beyond clearing, compared to sodium thiosulfate fixers. This is really
advantageous, because films that are fixed for less than 2x the
clearing time would be very slow to wash. Green and Levenson report
that plain gelatin coated film (no silver halide) impregnated with
exhausted fixer solution washes out faster than real film fixed for
any practical fixing time. This should tell you that cutting fixing
time is unwise, at least for films and RC prints.
Of course in case of fiber prints, there is a tradeoff with fixing
time, because as the fix time is prolonged more fixer goes into the
fiber, which in turn requires longer washing time. Again, it's
advantageous to use ammonium thiosulfate for 2x to 4x the clearing
time, as in the Ilford method, using rapid fix at film strength for 1
min. Using my homemade test emulsions, most chlorobromide emulsions
clear in about 10-15 seconds in my alkaline rapid fixer. Bromide paper
emulsions (0 to 0.5% iodide, depending on the formula) of enlarging
speed take up to 30 seconds to clear. (Tabular grain emulsions and
faster emulsions take longer time to fix, of course.) Fixer solutions
that reached the processing limit for Ilford fix-wash system can still
be used for RC prints and films, as long as the fixing time is
adjusted to ensure minimum of 2x the clearing time.
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