Re: Extravagatype and Na2

[Linas Kudzma <lkudzma@earthlink.net>]

Jeffrey,
  I originally thought that this precipitate was (NH4)2PtCl6 from exchange
with ammonium ferric oxalate. I think I read somewhere that the ammonium
salt is much less soluble. Your comment that the yellow precipitate is the K
salt is interesting. Is solubility data for the Na, K, and ammonium PtCl6
salts published?

I've used Na2PtCl6 in extravagatypes and coated normally despite the
precipitate. It still gives a contrast boost despite some of the chemistry
dropping out of solution. I must admit that coating a slurry bothers me and
must be wasteful. I doubt the precipitated salt is distributed evenly and
participating normaly in the image formation.

----- Original Message -----
From: "Jeffrey D. Mathias" <jeffrey.d.mathias@att.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, May 08, 2002 6:25 AM
Subject: Re: Extravagatype and Na2


> Erich Camerling wrote:
> > ... Sodium Chloroplatinate ( Na2PtCl6 , shortened  Na2 ) as a contrast
> > agent in standard Pt/Pd printing ...
> > But when I mix ( for instance ) 3 drops Ammonium Ferric Oxalate
> > ( 40g/100 ml H2O ) with 2 drops K2PtCl4 ( 20g/100 ml H2O ) and 1 dro
> > Na2 ( 20g/100 ml > H2O ) I immediately get a sediment ( yellow , I
> > suppose K2PtCl6 ( nearly > unsoluble ))
> > Richard wrote me that I was the first who mentioned this problem.
> > Other alt-photo-list members wrote about Na2 in PALLADIUM printing.
> > Has anyone of this group tried Na2 in Extravagatype ? And what was the
> > result ? I'm very interested.
>
> Your problem is that K2PtCl6 is only very slightly soluble in water.
> The metal double salt Richard wrote about for use to control contrast is
> Na2PtCl6.  These are very different.
>
> The yellow sediment and insolubility in water are a good indication that
> you did have K2PtCl6.  K2PtCl6 can also be found as an impurity in
> K2PtCl4 (the double salt typically used for platinum printing).  The
> best ways to avoid K2PtCl6 is to have a good manufacturer or source of
> the material and to not store or use it at temperatures in excess of
> 140F, especially in the presence of sodium.
>
> --
> Jeffrey D. Mathias
> http://home.att.net/~jeffrey.d.mathias/
>