Re: About HCA

nadeaul@nbnet.nb.ca
Sat, 10 Dec 1994 17:41:07 +0300

>There is a excellent book about photographic processing:
>
>" Modern Photographic Processing " by Grant Haist,
>Wiley-Interscience-Publication, 1979
>
>where you can find in Volume I a lengthy article about hypo elimination with
>several recipes.
>
>Thiosulfate elimination can be accelerated by the use of two cleasses of
>chemicals: (1) compound that act by physically displacing the thiosulfates
>from
>the photographic material by an ion-exchange action (i.e. diluted sulfite) and
>(2) compunds that react with thiosulfate, usually oxidizing it to a form that
>is
>more soluble (hypoclorite, hydrogen peroxide ...).

The problem with the alkaline peroxide approach is that it is a rough
treatment on gelatin and it also removes every last trace of thiosulfate.
It has been proved that a "small" amount of thio is actually desirable in a
print.

Luis Nadeau
>
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> | Dr. Rudolf Gschwind |
> | Inst. of Phys. Chemistry , University of Basel |
> | Scientific Photography Lab, |
> | Klingelbergstrasse 80, CH-4056 Basel, Switzerland |
> | gschwind@foto.chemie.unibas.ch http://www.foto.chemie.unibas.ch |
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