[pure-silver] Re: selenium toner mixed with HCA
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 9 Sep 2005 10:42:46 -0700
----- Original Message -----
From: "Eric Maquiling" <emaquiling@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, September 09, 2005 9:44 AM
Subject: [pure-silver] selenium toner mixed with HCA
I've read some posts looked at "The Print" as well as other
places.
Read instructions on the bottle of Selenium toner that I
have (not the
Kodak kind, something in a brown square bottle, hey it was
on sale).
What is the advantage of mixing selenium toner with HCA as
opposed to
just plain H20?
Looks like, in preparation for toning, I ordered some Sodium
Bisulfate
to make HCA. But just wondering what, if any, advantages or
disadvantages of HCA vs H20.
TIA!
--
Eric
There are two issues here. One is the use of an alkaline
bath before Selenium toning to prevent the precipitation of
elemental Selenium on the material being toned in the form
of a stain. This can happen under some combinations of
conditions when acid is transported into the toner as when a
print is toned directly after fixing in an acid fixer or
after only a short water rinse. The use of a pre-bath of
KHCA, or any mild alkali, will prevent this. This is
applicable to any concentration of Selenium toner. The
second reason, and the one that applies to highly diluted
KRST, is to combine the toning and wash aid steps. This is
the condition where dilution of KRST with KHCA is suggested.
When Selenium toner is used in stronger dilution than about
1:20 it should NOT be diluted in wash aid. Rather it should
be diluted in water and a wash aid or alkali bath used
first. The capacity of low dilutions of toner are
considerably greater than the diluted wash aid.
I have never seen any tests of washing efficiency of
prints or film treated in an alkali bath or sulfite wash aid
and toned in KRST without a subsequent bath in wash aid. The
toner does have some Ammonium thiosulfate in it but its not
acid. In a normal hardening fixing bath there are two
factors that tend to slow down washing. The first is a
binding or mordanting action of the white alum hardener. The
other is the general acid condition of the emulsion where
the electrical charges in the emulsion tend also to bind the
thiosulfate, although this has less effect than the alum.
By treating the emulsion in a bath that changes the pH to
neutral or aklaline both conditions are eliminated. When a
neutral fixing bath without hardener is used wash rates are
much greater than for a hardening bath. Sulfite has a
specific ion exchange action that speeds washing even when a
neutral, non-hardening, fixer has been used, but the effect
is much less dramatic than otherwise. For this reason I am
not sure the use of a wash aid following the Selenium toner
is really necessary. Also, because a neutral fixing bath has
no acid the use of an alkaline bath before toning is
probably not necessary. Note that many non-hardening fixing
baths (like Kodak F-24 are still acid). Acid is necessary in
a hardening fixing bath for the hardener to work but
non-hardening baths are usually made acid simply to insure
that carried over developer does not continue to be active.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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