Cleaning silver

My lab has been asked to conserve and clean a belt buckle used for
Greek costumes.  At first glance we thought the belt buckle was made
of an silver alloy.  However, SEM analysis revealed that it is a
copper/zinc/nickel/arsenic alloy (64.6% Cu, 20.4% Zn, 13.3% Ni, 1.7%
As.) There is no surface treatment, and the object is heavily
corroded on one side.  We observe a dezincification phenomenon with
the formation of two phases: one rich in Ni, As, and less in Cu and
the other richer in Cu but less in Ni and As.  So the object has
completely lost its composition on one side compared to the other.
The corrosion products have not yet been analyzed, but they adhere
well to the surface (so it is very difficult to remove
mechanically), and they are brownish-black in appearance.

We have tried several types of chemicals to try and remove these
corrosion products, such as EDTA, but nothing seems to work  I tried
a BCIN search, but have found little concerning the treatment of
this type of metal.  I am at the point where I will do nothing but
properly store the object.  But I thought I would ask if anyone has
come across a similar problem, and what they did in removing these
disfiguring corrosion products.

Vasilike Argyropoulos
Assistant Professor in metals conservation
T.E.I. Athens
Dept. of Conservation of Antiquities & Works of Art


                                  ***
                  Conservation DistList Instance 13:38
                Distributed: Wednesday, January 5, 2000
                       Message Id: cdl-13-38-016
                                  ***