[pure-silver] Re: Edwal Hypo Test and Poor memory
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 10 Jan 2011 14:52:15 -0800
----- Original Message -----
From: "Eric Nelson" <emanmb@xxxxxxxxx>
To: "pure silver" <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, January 10, 2011 10:56 AM
Subject: [pure-silver] Edwal Hypo Test and Poor memory
My bottle of Edwal hypo check test's instructions on the
bottle are worn off and
as I remember the instruction for testing paper rapid
fixer was to add a couple
drops to an ounce or so, (I used 10-20 mls in a graduated
cylinder) and
swirl the mixture. If the milkiness disappears, then
it's still good.
Can anyone confirm this from their bottle or experience?
Just want to make sure
my memory isn't completely awol.
Thanks
Eric
My bottle of HypoCheck is not available at the moment
but its not a reliable test anyway. Hypo Check is a solution
of iodide and forms silver iodide when added to the hypo.
The problem is that the reaction depends on the
consentration of the solution and, in any case, its not very
sensitive. Kodak has a formula for a similar test solution
in the _Black and White Darkroom Dataguide_ and elsewhere.
A much better test for the fixer is to fix out a scrap
of paper or film and use the residual silver test published
by Kodak. If the sample is washed before testing you can use
a 1:9 dilution of Kodak Rapid Selenium Toner rather than the
sodium sulfide solution in the published formula. The KRST
test fails if there is a lot of hypo in the emulsion so it
should be washed, at least briefly. If the fixer is working
the test should produce NO stain. Its used on wet but
blotted emulsion. Place a drop on a clear area and allow it
to stand for about one minute, then blot off. There should
be no visible stain. If used on a print wash the print as
you would after toning because the residue of the toner will
eventually cause a stain.
Here are some formulas for test solutions:
Kodak Fixer Test Solution FT-1
Water (at about 80F or 27C) 750.0 ml
Potassium iodide 190.0 grams
Water to make 1.0 liter
To test a single bath fixer. To 5 drops of test solution add
5 drops of fixing bath and 5 drops of water. Discard the
fixer if a yellow-white precipitate forms instantly.
Disregard any slight milkiness.
The instructions for two bath fixers do not make sense
and I think the dilutions are reversed. They recommend
testing the first bath with the same dilution as a single
bath but a greater dilution for the second bath. Since the
sensitivity of the test decreases with dilution I think this
is opposite of the correct practice. Kodak recommends taking
5 drops of solution, 5 drops of fixer, and 15 drops of water
for the second bath. I think probably this applies to the
_first_ bath and it is the second that is tested the same as
the single bath. In any case the dilution is known where it
is not for the Edwal test.
Also a liter of this stuff is a lifetime supply for an
army. Probably around 100ml is a more sensible amount.
Residual Silver Test ST-1
Water 100.0 ml
Sodium sulfide, anhydrous 2.0 grams
Store in a small stoppered bottle for no more than 3 months.
For use dilute one part of the above stock solution with 9
parts water. The diluted solution should be replaced weekly.
To use place a drop on a clear area of the print or film
and allow to stand for 2 to 3 minutes. Blot off with a
clean, white blotter. There should be no stain. Any
stainging indicates residual silver halide. Note that the
spot will stain with time so the test should be made on a
scrap of paper processed with the prints or on a clear
border of negatives.
The KRST test mentioned above is as effective and has no
odor but will fail to show a stain if there is much hypo in
the emulsion.
Residual hypo test, a test for completeness of washing.
Residual Hypo Test Solution HT-2
Water 750.0 ml
28% Acetic acid 125.0 ml
Silver nitrate crystals 7.5 grams
Water to make 1.0 liter
Note, use distilled water. Chlorine in the water will
combine with the silver to form a precipitate of Silver
chloride.
Store the solution in a screw-cap or glass-stoppered brown
bottle away from strong light at 65F to 75F (18C to 25C); it
will keep for about 6 months
Apply a drop fo the solution to a clear, unepsoed area
of the emulsioni sid eof processed film that has been
squeegeed or sponged. Allow it to stand for about 2 minutes.
Then rinse off the testg olution with water, blot the excess
water. The instructions are than to compare any stain to the
examples printed in the book. Kodak also made an estimation
strip with example stains. Some materials will show more
stain than others but there should not ever be a stong
stain. As with the other tests this one will generate a dark
stain with time. There is a more sophisticated version of
this test where the stain is fixed with salt, it can then be
compared for density using a densitometer and prepared
examples. The methylene blue test currently specified by the
ISO is more sensitive for quantitative testing but is too
complex for routine tests and this one works well enough for
routine darkroom use.
To test the effectiveness of a washer entire prints
should be fixed out, washed, and immersed in the test. It
will show if the washer is uneven in its effectiveness.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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