[pure-silver] Re: Using a selenium toner solution to test for residual silver
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 9 Jul 2010 09:54:02 -0700
----- Original Message -----
From: "Tom Kershaw" <tom@xxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, July 09, 2010 6:56 AM
Subject: [pure-silver] Using a selenium toner solution to
test for residual silver
From previous reading I understand that a dilute 10%
solution of Kodak Rapid Selenium Toner was recommended at
one point to test for residual silver on fibre base
photographic paper via placing drops onto the print
surface (checking for colour change) as an alternative to
a sulphide solution. Any thoughts on current knowledge
with regard to the effectiveness of this test?
Tom Kershaw
Kodak recommended a 1:9 dilution of KRST at one time as
an alternative to the sulfide test. This is for _all_
materials, not just fiber paper. The test solution is used
in exactly the same way as the sulfide test. The advantages
are that the shelf life is longer than the sulfide and it
does not have the rotten egg odor (hydrogen sulfide gas).
However, the test will fail if there is an excess of hypo in
the emulsion so it must be used on well washed materials
only. I don't think there was any other problem but the
suggestion disappeared from Kodak literature after a while.
I remember seeing somewhere that the color of the stains
from the KRST test actually matched the colors on the Kodak
Hypo Estimator strips better than the sulfide test but I
can't find that article. In any case I think the test is
still a valid way to check for completeness of fixing.
Note that either test will eventually cause a stain if
not washed out. For that reason its best to make a test on a
scrap of film or paper that has been gone through the usual
process.
The rate of fixing depends on whether the emulsion is
wetted before it goes in the fixer to material used to test
a fixing bath should be soaked in water for a few minutes
before being fixed. Kodak ran afoul of this when making
early tests on the effect of hypo concentration on fixing
time. Their early published results showed a peak in hypo
effectiveness at a certain concentration and slower fixing
with stronger solutions. It was discovered later that this
was an artifact of using dry emulsion and when wetted
emulsion was used there was no such peak and fixing time
continued to become shorter as fixer concentration was
increased.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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