[pure-silver] Re: Mystery Hypo Test
- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 25 Nov 2009 20:07:59 +0100
I need to be more accurate in my descriptions.
I use the two-bath fixing method. Both fixing baths are fresh fixer to
begin with. The 1st fix is used one-shot. The 2nd fix is promoted to
be the 1st fix for the next film, after which, it is also discarded. I
feel that for Tmax emulsions, this is the most certain way to have all
silver removed and no fixer by-products left.
Regards
Ralph W. Lambrecht
http://www.darkroomagic.com
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On Nov 25, 2009, at 06:20, Richard Knoppow wrote:
----- Original Message ----- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx
>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, November 24, 2009 4:49 PM
Subject: [pure-silver] Re: Mystery Hypo Test
Richard
I use the one-shot, two-bath fixing method for film.
Two fixing baths is excellent but there is no reason to use it one-
shot. One of the advantages of the two bath method is that it
extends the capacity of the fixer from about four to ten times. This
is probably more important for paper beause the type of emulsion
makes it more vulnerable to the effects of residual silver
compounds. According to Kodak KHCA also has the effect of extending
fixer life because it makes some otherwise insoluble complexes
soluble.
Some users of one-shot fixing use diluted fixer. The problem is
that they may not be getting complete fixing. It takes about three
free molecules of thiosulfate to make one molecule of completely
soluble silver complex. If there is not enough free thiosulfate in
the fixing bath it will not be able to completely solublize the
silver halide. Of course the same thing happens if the fixer is over
used. The advantage of the two bath system is that most of the
fixing takes place in the first bath and the second one remains
fresh enough to clean up after the first.
There is also the issue of dissolved iodide in the fixing bath.
Iodide tends to retard fixing. In a two bath system the iodide tends
to come out mostly in the first bath leaving the second one working
at full speed. Iodide used to be found mostly in film emulsion but
it is now also found in paper emulsions especially variable contrast
emulsions.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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