From: Sil Horwitz (silh@earthlink.net)
Date: 04/10/00-10:17:08 AM Z
At 2000/04/09 11:45 PM -0400, you wrote:
>Bob Kiss wrote:
> > I had a difficult time finding EDTA Tetra sodium here in Barbados, let
> > alone trying to find the EDTA you are speaking about.
> > ... Where can I get
> > some... .... Is there somewhere with an e-mail address who
> > could ship it to me? Or at least a fax #? ...
>
>The EDTA I used to mix with the sensitizer, I got from Vicente-M. Vizcay
>Castro mapa@ctv.es
>
>The EDTA(Na4) I used as a clearing agent, I got from John Melanson
>melanson@audiologic.cirrus.com
EDTA(Na4) is EDTA tetra sodium - very common substance, used in almost all
consumer laundry and washing products! If you have a commercial chemical or
industrial chemical source in Barbados (or certainly on one of the larger
islands) they should have the commercial grade, which is good enough for
photography. Its only purpose in life is as a sequestering agent - that is,
it can prevent two normally interactive ions from joining. In wash agents,
it is used to prevent the calcium and other metals from forming insoluble
salts with residual fixer. If you need to know proprietary names, the most
common one is "Sequestrene", but it is also commercialy known as Versene,
Tetrine, Trilon B, Calsol - try some of those on the laundry places: they
may actually be able to supply it. It is also a chelating agent (if I
recall my classic languages, the "chel" part means "claw") to form very
complex compounds of salts that normally react adversely. The most common
in photography is Ferric EDTA, used in color bleach-fix solutions in
conjunction with hypo (and ferric thiosulfate is insoluble, so you couldn't
dissolve hypo in an iron solution normally); the iron part reacts with
silver to form a salt, which the hypo then promptly dissolves. Ingenious!
(Hey - this is from the top of my head, and it's difficult to dig in there
in all the unused information!)
I've often wondered if ferric EDTA could be used as the iron ingredient in
alt photography, but have never had the time to research the field and do
the experimentation. Perhaps someone on the list has tried this?
<<sil>>
<silh@psa-photo.org>
<webmaster@psa-photo.org>
Sil Horwitz, FPSA
Technical Editor, PSA Journal
check out <http://www.psa-photo.org>
personal page: http://home.earthlink.net/~silh/
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