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Anealing Argentium Sterling in Kiln


#1

Hello,

I am trying to find some on annealing large coils of
Argentium sterling wire with a kiln. I’ve found reference to the
necessary temp for furnace annealing, 1100F, but no reference to time
held at that temp. Does the temp need to be raised gradually or do
you just introduce the wire in to the preheated kiln?

Thanks in advance,
Tracey Bell


#2

5 min at 1100 will do. But that means the kiln has to recover to
1100 after you put the wire in it before you start counting time. And
even though Argentium is not prone to firestain I think you will
still need some way of keeping it free from oxygen at these elevated
temperatures if you don’t want to have problems with the metal in
working it later.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#3

Hi Tracey,

I don’t think it matters whether you put the wire in the kiln cold,
or whether you put it in at annealing temperature. The length of
time depends on how tightly coiled the wires are, how thick the
gauge, etc. You could use the same cues that I recommend for torch
annealing: when black marker has disappeared, and/or the metal turns
whitish, and/or Handy paste flux is clear and fluid, but still
bubbly (see my article Road Testing Argentium Silver that is here on
Ganoksin for images). It IS important how how you take it out of
the kiln. Lift the wire out by picking up the board it’s on, rather
than picking up the coil of wire with tongs.

Cynthia Eid
http://www.cynthiaeid.com


#4
5 min at 1100 will do. But that means the kiln has to recover to
1100 after you put the wire in it before you start counting time.
And even though Argentium is not prone to firestain I think you
will still need some way of keeping it free from oxygen at these
elevated temperatures if you don't want to have problems with the
metal in working it later. 

I agree that 5 minutes is a good time estimate. Though I hesitate to
disagree with Jim Binnion, I disagree with the idea of keeping it
free from oxygen. It is GOOD to expose Argentium Silver to oxygen—
That allows the germanium to form germanium oxide and allows the
germanium to grab oxygen from the copper. Germanium oxide does not
allow oxygen to penetrate inside the metal, thus preventing
firescale.

Cynthia Eid
http://www.cynthiaeid.com


#5

Hi Cindy,

I agree that 5 minutes is a good time estimate. Though I hesitate
to disagree with Jim Binnion, I disagree with the idea of keeping
it free from oxygen. It is GOOD to expose Argentium Silver to
oxygen--- That allows the germanium to form germanium oxide and
allows the germanium to grab oxygen from the copper. Germanium
oxide does not allow oxygen to penetrate inside the metal, thus
preventing firescale. 

Oxygen atoms are so small that they easily move in the metal lattice
between the metal atoms. Silver has a great affinity for oxygen and
oxygen easily moves in the silver matrix. Oxygen will penetrate if
there is no barrier (flux) it then combines with the germanium as
you say and creates germanium oxide. Once the oxide is formed it will
not easily break apart (reduce) and that germanium atom is no longer
available to bind with oxygen. So the question is how much time will
it take to oxidize all the germanium? Does germanium oxide form a
boundary layer that prevents oxide penetration like chromium does on
stainless steel? I don’t know, but I do not believe there is enough
germanium in the alloy to form and effective barrier. Maybe Sam
would have some data about what happens to the microstructure with
repeated exposure to oxygen at high temperatures. But in general it
is not good for any metal to have repeated exposure to high
temperature oxygen.

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#6

There is a new site for Argentium Silver that has a LOT of
It looks like everything that has been written has been
gathered at, or linked to, the new site. The url is:
www.argentiumsilver.info

The site includes a Library of articles, data sheets, technical
reports, and working guides.

In the Reports section of the library are a number of papers by
CATRA, which is an independent testing association in Great Britain.
CATRA has tested Argentium Sterling for tarnish and firescale
resistance, and compared Argentium Sterling to U.S. alloys and
European alloys. The reports are in downloadable pdf formats. The
British tend to use the word firestain instead of firescale, so the
firescale report comparing Argentium Sterling and US alloys is
titled: CATRA report 963443B: ‘Resistance to Firestain Evaluation of
Silver Alloys’.

During the firescale tests by CATRA, the silver samples were heated
at 1076 F 580 C (580 C) for 1 hour. The procedure description in the
report mentions that the kiln door was left slightly open to allow in
oxygen. This confirms the suggestion I made in a previous post, that
it is good to have oxygen present when kiln annealing, as well as
torch annealing.

For anyone interested in Argentium Silver, it is nice to have one
source for all now!

Cynthia Eid
http://www.cynthiaeid.com


#7

Cindy,

The resistance to firestain of argentium is not the issue. The reason
that you cannot see an oxide layer in the micro-graphs shown on that
site is that germanium oxide has about the same color as the bulk
metal where the copper oxide has a darker color that stands out. The
oxide is still there you just cannot see it. The question I have is
what is the affect of the greater presence of oxide in the metal on
the working characteristics. I know that copper oxides have a
detrimental effect on the ductility of standard sterling. I am
assuming that germanium oxide is similar in that the metal now has
particulate mater that is not in solution in the crystal matrix.
This leads to reduced ductility. This is my reason for suggesting
flux with argentium not firestain prevention

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#8
... The question I have is what is the affect of the greater
presence of oxide in the metal on the working characteristics. I
know that copper oxides have a detrimental effect on the ductility
of standard sterling. 

I’ve formed and drawn a lot of Argentium Silver (AS) and I can’t say
I’ve ever seen fracturing or whatever you’d expect from this
"detrimental" effect of the oxide. In fact I’ve seen that AS is
noticeably more ductile than regular sterling – I’d guess-timate as
much as 40 or 50% more when it comes to simple wire drawing – and
that’s with as much oxide build-up as one is likely to get (repeated
annealings without pickling).

While I have no doubt that your supposition is technically true, I
have serious doubts that it has much effect in practice.

Cheers,
Trevor F.
in The City of Light
Visit TouchMetal.com at http://www.touchmetal.com