From: Kris Erickson (kerickso@ryerson.ca)
Date: 01/20/03-09:52:48 AM Z
Thanks Scott and Finn,
Checking out the Stevens book I decided to go with his 3rd recipe for
synthesizing ferric oxalate (I think it's the one with ferrous ammonium
citrate, oxalic acid and pot. permanganate).
Scott, your & Mike's reason for NOT going with the fe amm. ox is
gratefully noted. I have a slight aversion to poisonous sludges.
Cheers,
Kris
Scott Wainer wrote:
>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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