[pure-silver] Re: Hypo Test Sensitivity
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 28 Jun 2006 18:54:46 -0700
----- Original Message -----
From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
To: "PureSilverNew" <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, June 28, 2006 2:39 PM
Subject: [pure-silver] Re: Hypo Test Sensitivity
Richard
That was my understanding too, but the HT1 test seem to be
well and alive in
Continental Europe. It is preferred to HT2 and according to
German amateur
literature, far more sensitive than the silver-nitrate test.
Amaloco, a
Dutch manufacturer of photographic chemicals, sells a
version of HT1, called
H15. As far as I know, only SilverPrint in London still
sells a version of
HT2.
I'm currently investigating the differences.
According to Levington (1957?) and Haist (1979?),
equilibrium, during
diffusion washing, is reached within 5 minutes or so. That's
the foundation
of the Ilford Washing Technique. If that is so, hypo is not
bound to the
emulsion, and HT1 is a valid test (true?). According to
Amaloco, H15 is
sensitive down to 0.001 g/l hypo. That's roughly 100x more
sensitive than
HT2, which goes down to about 1 µg/m^2. This comparison is
admittedly
assumes equilibrium with the surrounding wash water again.
Unfortunately, I know nothing about the methylene-blue test,
but a test, not
practical for 'the rest of us', is only of academic interest
to me anyway.
That's why I'm concentrating on the comparison of HT1 vs
HT2.
Who knows more about the pro and cons of HT1 vs HT2?
Regards
Ralph W. Lambrecht
http://www.darkroomagic.com
I think Ryuji Suzuki can give you a better explanation of
how hypo can be bound up with both the gelatin and silver in
an emulsion. It can also be bound mechanically by the fibers
of paper print supports. The basis of the Ilford archival
washing method is the idea that the hypo takes about a
minute to become embedded in the paper fibers so that the
effect can be eliminated by reducing fixing times to below
one minute. That will not work for some papers.
I'm not quite sure what is meant by equilibrium being
reached in 5 minutes. In a running water wash equilibrium is
never reached although was rate can become very slow. In
still water the time to reach equilibrium probably varies
with the volume of water. Washing of the emulsion is a
diffusion process. The thiosulfate moves from an area of
higher concentration to an area of lower concentration, the
rate depending on the difference in concentration and
becoming slower as equilibrium is approached. As washing
continues the concentration in the emulsion becomes less so
taht the concentration in the wash water must be very low
for the process to continue.
In the paper support the hypo can become mechanically
bound to the paper fibers so that it no longer leaves the
support by a purely diffusion process. That is why washing
of fiber prints takes so long even when a wash aid is used.
The wash aid has a relatively small effect on the support
compared to the emulsion.
Two mechanisms of binding are the "mordanting" effect of
Potassium aluminum sulfate hardener, the common "Alum"
hardener found in fixing baths. It specifically binds
thiosulfate over a range of pH lower than about neutral. A
second mechanism is binding by electrical charges in the
emulsion when it is on the acid side of its isoelectric
point. A sulfite wash aid helps with both of these.
The original test for residual hypo uses the following
formula:
Kodak HT-1a
Distilled water 180.0 ml
Potassium Permanganate 0.3 gram
Sodium Hydroxide 0.6 gram
Distilled water to make 250.0 ml
This solution is diluted 1.0 ml of solution to 250.0 ml of
water. The runoff water from approximately 80 in^2 of film
is allowed to drip into this mixture for 30 seconds. If hypo
is present the solution will turn orange or yellow in about
30 seconds after adding the drip water.
There are additional instructions for measuring the
residual hypo in paper. Since certain orgainic material in
the water may have the same result as hypo a method of
testing for it is given. No specification of the sensitivity
of the test is given.
This formula is still given in the 1946 edition of the
Kodak Processing and Formulas booklet.
By the mid 1970s it was replaced by HT-2, the silver
nitrate test:
Kodak HT-2
Water 750.0 ml
Acetic Acid, 28% 125.0 ml
Silver Nitrate 7.5 grams
Water to make 1.0 liter
A drop or two of this solution is placed on a clear area of
a negative or print and allowed to stand for about 2
minutes. Swab off. It should leave very little stain. Kodak
published a "Hypo Estimator" for years which had color chips
for comparison with the stain to give some idea of the hypo
content. The test can also be made permanent by a treatment
in Sodium chloride and the hypo level measured by
densitometric means.
I have forgotten the specifications but my memory is
that it is a very sensitive test.
The current method for testing residual hypo is the
Methylene Blue test.
I think the first author is G.I.P. Levinson. Levinson,
with others, did extensive research into fixing and washing
at Kodak labs.
AFAIK, the old permanate test has been considered obsolete
for quite a long time. It does not measure the residual hypo
in the film or paper, only what's in the wash water and that
can be very misleading. The silver nitrate test reacts with
the hypo actually in the emulsion or in the support so it
can show up hypo which is bound up in some way.
BTW, the test can be used on the support as well as on
the emulsion.
I suspect the European sources you mention are in the
process of re-inventing the wheel.
Ryuji sent me some copies of papers describing the
Methylene Blue test. I have them filed away and will look
for them.
I suspect he will have much more detail about all of this
if he chooses to respond.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account (the same e-mail address and password you set-up when you subscribed,)
and unsubscribe from there.
Other related posts:
