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Oxidizing Keum Boo


#1

I have been reading about Keum Boo and various methods of fusing
gold to sterling silver, and in particular depletion gilding. That
is, the silver is heated in an oxidizing flame and quenched in pickle
several times to remove alloy from the surface, leaving fine silver.
Question: has anyone tried using any of the oxidizing solutions used
to patinate silver for the oxidation part?

Todd Welti
Research Acoustician
Harman International Industries
Northridge, CA
(818) 895 8124
@Todd_Welti
TWelti@harman.com


#2
     I have been reading about Keum Boo and various methods of
fusing gold to sterling silver, and in particular depletion
gilding.  That is, the silver is heated in an oxidizing flame and
quenched in pickle several times to remove alloy from the surface,
leaving fine silver. Question: has anyone tried using any of the
oxidizing solutions used to patinate silver for the oxidation part?

those solutions are not actually producing an oxide. they produce a
mix of silver and copper sulphide. The trouble with the approach is
that the silver is almost equally affected, so “oxidizing” with such
a solution, and then somehow chemically removing the sulphide, would
not result in enriching the surface with silver and depleteing it of
copper. The heat works because only the copper oxidizes, being then
selectively removed by the pickile, leaving silver only. In addition,
the heat method creates a much thicker copper free silver surface
layer, since during heating, unoxidized copper just below the surface
can diffuse towards the surface. One stops the process when the
silver no longer turns black on heating. this happens not when just
the surface copper is gone, but when it’s gone from a deep enough
thickness into the silver surface that significant copper is no
longer making it to the surface to oxidize. So the fine silver layer
is much thicker and more durable than a chemical treatement alone
would be.

Peter