From: Finn Ugor (finnugor729@hotmail.com)
Date: 01/20/03-05:12:18 AM Z
Kris and Scott,
It was probably me in the archives who queried about the precipitate after
using AFO for kallitype. I am glad that Scott got an answer from Mike Ware
to my original question. Though I responded to the situation the same,
without knowing the chemical processes underlying the precipitation: I
quited using AFO for kallitype for the reasons Mike Ware metioned despite
the resulting prints were acceptable as I recall.
Istvan Bibo
from Hungary
>From: Scott Wainer <smwbmp@starpower.net>
>Reply-To: alt-photo-process-l@sask.usask.ca
>To: alt-photo-process-l@sask.usask.ca
>Subject: Re: Ferric *ammonium* oxalate for kallitype?
>Date: Tue, 14 Jan 2003 17:27:37 -0500
>
>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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