[pure-silver] Re: Mystery Hypo Test
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 23 Nov 2009 16:48:30 -0800
----- Original Message -----
From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, November 23, 2009 9:19 AM
Subject: [pure-silver] Re: Mystery Hypo Test
Richard
I'm looking for a more reliable hypo test for films
without having to
go to methylene blue. As far as I know, HT-2 is very
useful for paper
but virtually useless for films, because the stain cannot
be
quantified on clear film. Consequently, HT-2 is not a good
replacement
for HT-1.
I also think that HT-1 accuracy is underrated. Its
application is
usually published the same way you described it, with
limited
accuracy, because it tests the wash water and not the
emulsion itself.
However, when modifying the test slightly, it can deliver
amazing
sensitivity. I modified the standard test procedure as
follows:
I immerse a fully washed film into a 0.5-liter bath of
distilled
water. With light agitation, let it soak for 6-10 minutes,
after
which, the residual thiosulfate is fully diffused and an
equilibrium
between film and wash water is reached. In other words, at
that point,
the thiosulfate concentration of the wash water is the
same as that of
the film emulsion.
This way, I can detect down to 1 mg/l of hypo with HT-1,
which is
sufficient, because a typical 35mm or 120 roll film has a
surface area
of roughly 80 in^2 or 0.05 m^2. If it has been washed to
the archival
standard of 15 mg/m^2, and the residual thiosulfate of one
roll film
(0.75 mg) is fully diffused in 0.5 liter wash water, the
thiosulfate
concentration of the water must be at or below 1.5 mg/l.
I was hoping to have found an even more accurate test with
this
Crabtree formula, but it may not work.
You are assuming that there is no hypo bonded to the
gelatin or image silver. Where acid hypo has been used this
is possible. Binding is less of a problem for film than for
fiber paper where hypo can be bound up in the baryta layer
or in the fiber structure of the support. The permanganate
test was discontinued because it was simply not effective.
The silver nitrate test is better. I will see if I can come
up with some citations.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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