RE: Test for Silver Metal in Print?

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From: Etienne Garbaux (photographeur@softhome.net)
Date: 10/29/03-12:42:06 AM Z


Liam wrote:

> I recall from somewhere that toning (with gold, at any rate) results in
> the partial replacement of silver, this silver being converted to the
> chloride (taking Cl from the gold chloride) as gold deposition takes
> place, and that this is one reason why prints should be fixed after Au
> toning.
>
> If so, then maybe a coating of AgCl as well as gold on the silver grains
> is another limiting factor, and perhaps toning could be taken a bit
> further if toning is continued after a short fix?

I'm not sure that traditional toners rehalogenate image silver. Even if
they did, the AgCl would not be adsorbed onto the silver grain and should
not prevent further access by the toner.

Toning appears to be self-limiting -- as more of the surface of a grain
becomes gold [platinum], the toning action slows. When essentially all of
the surface is gold, toning stops. And gold [platinum] apparently never
replaces the internal silver atoms in the grain. This hypothesis is
supported by empirical results -- leaving prints in toner indefinitely does
not increase toning beyond a certain point.

The potentially unintuitive finding is that no matter how long one tones,
one never builds up an impermeable shell that completely prevents corrosion
of the internal silver (although protection with respect to corrosive
agents in the substrate and the display environment appears to be
substantial).

Best regards,

etienne


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