------- Forwarded Message Follows -------
Date: Fri, 16 Feb 1996 22:20:39 +1100
Reply-to: alt-photo-process@vast.unsw.edu.au
From: Mike Ware <mike@mikeware.demon.co.uk>
To: Multiple recipients of list <alt-photo-process@vast.unsw.edu.au>
Subject: Dichromate in Developer for Palladium (was Re: paper test data for palladium)
I'm interested - and not a little surprised - to learn of the use of an
oxalate developer for platinum/palladium which contains dichromate to
'control' contrast.
The reaction between these two ions is well-known to inorganic chemistry,
and is indeed one of the standard methods for preparing a whole range of
oxalato- complexes of Chromium(III). Admittedly the lab preps entail
heating, but this is just to speed up the process. I doubt that any
solution containing the two will remain unaltered for very long, even at
room temperature.
Keith has just described one consequence:
>KOx does not become
>exhausted. I don't know about the dichromate. I have found some green
>needle-like crystals in one of the bottles.
This is, very probably, potassium tris-oxalatochromate(III): K3Cr(C2O4)3.3H2O
The other consequence is that when the Cr(VI) of dichromate is thus reduced
to Cr(III) it will cease to have a 'contrast enhancing' effect.
Mike