[pure-silver] Re: Hypo Test Sensitivity
- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
- To: PureSilverNew <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 29 Jun 2006 22:45:35 +0200
Thanks Richard
This was a big help. I'm interested in the details of the methylene-blue
test but are afraid that I can't conduct it myself. However, I have limited
access to professional and university labs, who might be able to help.
I found out through Peter Loeffler from Phototec that Amaloco is selling H15
(HT1 variant) since the 1950s, but they are aware and don't hide the fact
that the test has limited sensitivity.
For reasons I fail to understand at the moment, the accepted residual
thiosulfate limit in the German amateur press is far above the ISO standard
(5 vs 1 µg/m^2).
We are suffering from closed research departments at Kodak, Ilford and
Agfa!!!
Regards
Ralph W. Lambrecht
http://www.darkroomagic.com
On 2006-06-29 03:54, "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> wrote:
>
> ----- 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
>
>
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