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Re: platinum/palladium coating

Yes, it is a good idea (smart) to add any contrast agent just prior to
coating.  I was in fact referring to the other components.  Mike Ware writes
in the Ware/Malde ammonium system that the solution of platinum salt and
ammonium ferric does produce a richer print if allowed to mature for an hour
or so.

I try not to get any one in the habit of allowing other solutions to sit
around prior to coating.  I have not run any test on a "mature" solution
with the lithium palladium. I suspect that would not be a good idea.
Perhaps Carl or Dick may know for sure.

The "better" was a subjective thing, allowing for others to make up their
own minds about what makes one print better or make acceptable than another
and how someone might work.

I would suggest that any premixed coating solution be kept in their own
brown bottle with or without a dropper.

Eric J. Neilsen
4101 Commerce Street, Suite #9
Dallas, TX 75226
214-827-8301
http://e.neilsen.home.att.net
http://www.ericneilsenphotography.com
----- Original Message -----
From: "Jeffrey D. Mathias" <jeffrey.d.mathias@worldnet.att.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, April 07, 2001 7:22 AM
Subject: Re: platinum/palladium coating


> Eric Neilsen wrote:
> > [I had written:]
> > > Another important consideration is to apply the coating mixture
> > > immediatly after mixing.  Do not mix a coating solution and let it sit
> > > around before coating as several things could go wrong.
> > >
> > I don't agree with this point.  There are some mixtures that can sit for
> > several hours and produce better prints.
>
> Yes there are.  However, some considerations are:
> +  If the metal salts must be heated to keep them in solution, once
> mixed with the other coating ingredients, they could (sometimes and more
> likely if at higher concentrations) precipitate back out in a matter of
> minutes.
>
> +  I have noticed a few times the if a coating mixture sits for a while
> (over an hour) sometimes crystals form, showing up in the mixture and as
> particles while applying the mixture.
>
> +  Contrast agents can adversely impact the metals salts and the
> sensitizer, especially over time.  It is recommended to not add contrast
> agents to the stock sensitizer solutions nor the metal salt solutions.
>
> +  I have found it to make a difference WHEN (the order of) the contrast
> agent is added to the coating mixture.  To avoid possible problems, the
> order of mixing should be sensitizer, metal salts, contrast agent.
>
> +  I have not studied changes in prints as the coating has sat for
> various times, but I do suspect that with the "better prints" Eric
> refers to, the coating solution may not have reached a steady state
> condition.  Therefore control of ambient conditions and timing of the
> sitting (resting, maturing) of the coating solution may be needed to
> provide for consistency of the results.  Also covering the mixture to
> prevent contamination or evaporation is a good idea.  And when maturing
> a coating mixture, one may consider adding in the contrast agent
> immediatly prior to using.  But then, it could even be some effect of
> the contrast agent that is at work.
>
> --
> Jeffrey D. Mathias
> http://home.att.net/~jeffrey.d.mathias/
>