From: Richard Urmonas (rurmonas@tpg.com.au)
Date: 10/31/03-07:18:27 AM Z
On Thu, 30 Oct 2003 03:18 pm, you wrote:
> Regarding the print that was toned in the strongest toning solution
> (10ml of a 20% palladium solution per liter of toner), the measured
> reflective density before bleaching was 1.42, and after bleaching it
> was 1.36. This means that the palladium in the print, whatever its
> form, was contributing about 96% of the total density of the print
> before bleaching, with 4% coming from the silver. This is actually
> quite a bit higher than I anticipated after hearing of the results of
> Etienne with other processes.
Sandy,
Two points about this bleach test:
1) Density is a logarithmic scale, so the density drop is actually 13%.
This may not relate directly to silver content as the optical density
of silver and palladium may differ. Further if we have the case
where a silver "grain' has been plated with palladium the silver could be
removed from inside this shell with no change in optical density.
So I would exect the 13% density shift to indicate a minimum of 13%
silver. I guess to be more exact, would require weighing the
"coating" before and after bleaching, as someone else on this list
has done.
2) My experience with ferri - bromide bleaches is that the density
of the bleached image can vary significantly. When bleaching
a silver-gelatine print I can end up with anything from a very pale yellow
image, through to a dark brown image. I would suggest redoing the
test with a process which dissolves and washes away the silver, rather
than simply bleaching it. Perhaps the nitric acid others have mentioned.
Richard
--- Richard Urmonas
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