Cleaning silver

V.A. ask  about chemicals to remove the corrosion products of a belt
buckle thought firstly silver, but actually a Cu alloy with Zn and
Ni.

I found in the literature (Beizen von Metallen, R. Rituper , 1993,
page 257) a reference about "Neusilber" (newsilver), a special brass
with zinc and another metals. They recommended a three step etching
procedure:

    1.   H2SO4, 10%, 60 deg. C
    2.   H2SO4, 10%, RT
         Sodium dichromate, 3-9% w
    3.   H2SO4, 10-15%, 60 deg. C

Caution: this is a *etching* solution, i.e, even if it works for the
corrosion products it will also etch the metal!

How I have not personally worked with these system, I recommend  a
lot preliminary tests to know very well the possible reactions: the
use of more diluted solutions and coupons of similar alloys would
be a good idea.

Prof. Dr. Virginia Costa
15 rue Jules Hetzel
92190 Meudon
France
+33 1 46 23 19 40 (phone/fax)


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                  Conservation DistList Instance 13:39
                 Distributed: Monday, January 10, 2000
                       Message Id: cdl-13-39-005
                                  ***