Is germanium oxide not just transparent but also invisible? How do
you determine that the germanium oxide is 2mm thick? Is there some
scratch test, chemical test, microscopic examination or the like
that we can do (in our ordinary workshops) to determine when we
have maximized the germanium oxide on or below the surface?
I'm sorry that there seems to be so much confusion over this oxide
issue with Argentium Silver. I suspect this is happening because the
alloy, and some of the metallurgy related to it, is new to us and
not yet fully explored.
Germanium oxide is a largely transparent oxide that forms on the
surface of Argentium Sterling (AS) when you heat it. I don't know
the thickness of this layer but my guess is that we're taking
micrometers thick, as in some several millionths of a meter. Regular
sterling forms oxides on the surface too, they just happen to be
copper oxides, are colored red and black and are therefore very easy
to see. The process is the same, the results are a little different.
The tarnish resistant "skin" that forms on AS is not the germanium
oxide layer that forms on the surface. This "skin" is the metal near
the surface, going to as deep as 2mm or more, that exhibits high
What is the exact composition of that tarnish resistant "skin"? I
don't know, but it's been recently speculated that there may be a
disproportionately high occurrence of groups of copper atoms bound
by a germanium atom, a property of germanium which is quite probably
contributing to the tarnish resistance we are seeing. These Ge-Cu
groups would likely y be formed when the metal is heated. (Heating
AS has been proven to cause the Ge atoms to migrate, generally
speaking, towards the surface.) Again the exact processes going on
here are unknown. But no, this layer is not "invisible", it's just a
sterling alloy that seems to have a lot of germanium at work in it.
Are there ways to tarnish test? Of course there are, a wide variety
of such tests are used throughout the industry. I've come up with a
way or two to do bush-league tarnish testing in my studio and AsCo
(Argentium Silver Company) has suggested another good method. I
respectfully direct you to my blog,
http://www.touchmetal.com/blog/argentium-blog.html, and the "tarnish
testing" posts there for details.
In fact it was these tests that demonstrated to me the presence of
the tarnish resistant "skin" that forms on AS. When I put a
cross-section of a thick plate of heat treated AS into the tarnish
test I saw that the outer edges did not tarnish (or tarnished very
little) while the interior metal, which would have been fully
protected from the atmosphere during heating, tarnished as you might
expect regular sterling to. Apparently something causes the metal
near the surface to transform in such a way as to render it tarnish
Since I've seen this tarnish resistant layer become as thick as 2 mm
or more after repeated heat treating cycles I've taken to calling it
a "skin" on the metal, for lack of a better name. Just to be
perfectly clear, this tarnish resistant "skin" on the AS is not
invisible, it looks like regular sterling silver, or rather it just
looks like AS. It is only the tarnish tests that reveal it to behave
different than you'd expect regular sterling to behave.
In order to determine the effectiveness of your heat treatment of AS
you'll need to test it, that's why the tarnish tests are worthwhile.
Fortunately they are easy to do and quickly show you how tarnish
resistant your metals actually are. As a general rule I have
observed, and this has NOT yet been confirmed by others, that one
can improve the tarnish resistant properties of AS by repeating the
heat treatment cycles. Specifically this seems to thicken the tarnish
resistant "skin" I've talked about.
Finally I'd like to make it clear that that all of the above are
simply observations from the studio while working with the metal.
Beyond that we'll all have to wait because the lab work required to
give us deeper insight into the alloy and it's metallurgy lies in
in The City of Light
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