From: Scott Wainer (smwbmp@starpower.net)
Date: 01/14/03-04:27:37 PM Z
Hi Kris,
Being of interest to me, I contacted Mike Ware to satisfy my curiosity. Here
is what he said:
"... The unfortunate fact is that any system containing silver ions and
oxalate ions will, sooner or later, precipitate silver oxalate, which is
quite insoluble (much more so than silver citrate). The situation is worse
with ferric ammonium oxalate, which tends to release more free oxalate (3:1
ratio) , than with ferric oxalate (3:2 ratio), where the release can be
delayed or suppressed, especially if there is excess ferric ion present (see
Dick Stevens book). Of course, ferric ammonium oxalate is by far the most
desirable salt to use for the sensitizers, for several reasons, and most of
my methods are based on it. But I know that mixing it with silver salts
always gives a precipitate, and although this sensitizer slurry is said to
"work" up to a point, I find it inelegant and unacceptable to use a
suspension of solid to coat plain paper with, hence the
argyrotype -reluctantly - uses ferric ammonium citrate. I have tried various
complexes of the silver and the iron to prevent precipitation with oxalate,
but no workable method has yet emerged. ..."
Since the precipitate is insoluble silver oxalate it would not be able to be
removed from the print during washing. Besides being a poisonous residue
left on the print, it might react unfavorable with the image - making it
less archival and prone to deterioration. I guess I will stick to fac and
ferric oxalate for VDB and Kallitypes.
Scott Wainer
smwbmp@starpower.net
<copied>
Hi all,
Happy New Year--
My local supplier for chemicals just told me it may be a 3 to 4 week
delay for ferric oxalate (gasp!)
He did say that there was some ferric _ammonium_ oxalate
available--searching the archives, someone on this list queried about a
precipitate that formed as a result of using it in kallitype (spec. with
the silver nitrate). He said, however, that the image "seemed" to be a
fine kallitype print; he did not receive any response to his post, so I
do not know how the matter was resolved.
Can anyone shed a little light on the matter for me, and perhaps others
on the list?
thanks,
Kris
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