Silvered brass

I recently posted the request for a problematic silvered brass
(Conservation DistList Instance: 16:70 Monday, May 12, 2003). Some
interesting information had been developed off line and I think some
feedback may be interesting for the community.

Most of the comments help to struggle between the technique of
patinas itself. Actually the conclusion of this thoughts is that we
are facing a photographic treatment applied directly to the silvered
layer. We found evidences for this direction and are in the process
to analyse samples in order to determine any traces of palladium,
selenium, gold or other process possibly used.

This direction was encouraged by the observation that the layer is
now photosensitive and left traces that it had been applied by a
masking film that reproduced the scissors marks. In parallels, no
brush marks were found on close investigation.

Some of the questions I received can be summarized by this
following:

   "You mentioned a treatment with potassium cyanide or something
    what is the exact process, never heard about It."

The intention of this diluted solution enriched by a wetting agent,
will be to soften the oxides, blisters included, and to remove any
traces of recent oxidation. If the dark layers were to be patinas,
the risk to remove those chemicals will be great. But according to
the result of the analyses, if we are facing a metallic film,
according to the reactivity and the electronic reactivity in ratio
to silver, a rate may be found as to select oxides only and though
reinforce any left contrast of the pattern. Blisters are treated by
the same manner with a possible need to mechanically help the flake
to flatten. Thorough rinsing and PH neutralisation will be obviously
be a must treatment followed by a real drying of the porosities. The
necessity to create a film barrier should be seriously considered.
Potassium cyanide is a violent solvent to reduce silver as fare as
my experience goes. Although I never applied it to any conservation
treatment and will be rather reluctant to do so, and do not drink.

The aim of my question on the list was to exchange possible
experience or theoretical thoughts regarding the complex approach of
this problem.

David Cottier-Angeli
Metals Conservation and Jeweller


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                  Conservation DistList Instance 16:72
                   Distributed: Monday, May 19, 2003
                       Message Id: cdl-16-72-004
                                  ***