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Heat-hardening copper


#1

Can copper be heat-treated to harden it in the same manner as
gold and silver?

Rene Roberts


#2

It is my understanding that pure metals such as copper, silver
and gold cannot be heat treated like karat gold and sterling
silver can.

Alan Revere
Revere Academy of Jewelry Arts
San Francisco


#3

It is my understanding that pure metals such as copper, silver
and gold cannot be heat treated like karat gold and sterling
silver can.

I dunno, but copper certainly work-hardens, and can be made
malleable again by annealing.

Al
mailto:@Alan_Balmer


#4

Can copper be heat-treated to harden it in the same manner as
gold and silver?

Pure copper cannot be heat treated to harden it. You can get a
beryllium copper alloy which is almost pure copper, and is made
specifically to be heat treated to a springlike state. Once
hardened, annealing it again is tricky. The downside to this,
and it’s a BIGGIE, is that beryllium oxide is VERY toxic. This is
NOT an alloy you want to be using in normal jewelry fabrication
without knowing a good deal about it, and taking great pains to
avoid producing dust, grindings, etc, that you could breath in.


#5

Hey, Believe us Al. Alan’s post is being modest in his wording.
He DOES know. (Or at least, he’s got most of us fooled into
believe it (grin))

Work hardening a metal is not the same as heat treating a metal
for hardening. Not at all the same. heat treating non-ferrous
metals relies on precipitation hardening. In most cases we’re
interested in, this means causing copper to come out of solution
in the parent metal in such as way as to increase the hardness of
the alloy. This works with sterling silver, and with many karat
golds. Certain platinum alloys have also been developed (By Steve
Kretchmer, notably, who first developed these for his tension
settings) to allow a similar type of heat treatment.

Pure metals obviously do not have a second componant which can
be brought out of solid solution to cause this hardening effect.

Pure silver, pure gold, pure copper, etc., all can be work
hardened to some degree. And when work hardened, they can then
be annealed. But they cannot, by heat treating, be hardened
again to any significant degree. Overannealing will cause some
grain growth, and large grained material may be somewhat less
workable than fine grained material, but the main difference is
that coarse grained metal will tend to give you an orange peel
effect when you bend or work it, while fine grained won’t, There
isn’t so much actual difference in hardness. At least not in
pure metals. Tin/pewter is the main exception to that statement
that I’m aware of, in the metals we use in jewelry. As cast,
coarse grained tin or pewter is quite considerably harder than
worked or rolled metal…

Alan’s fine book, “Professional Goldsmithing”, has a very nicely
detailed chart in the apendices of various alloys and the
hardnesses that can be obtained by heat treating them.

Peter Rowe


#6

Peter, thanks for that explanation of heat hardening. I
suspected that “no” was the answer, but now I know the reason.
Since you mentioned coarge-grained metal, once a metal is in the
state where you get the orange-peelies when you bend it, can it
ever be made workable again?

Rene Roberts


#7

Since you mentioned coarge-grained metal, once a metal is in the
state where you get the orange-peelies when you bend it, can it
ever be made workable again?

Rene,

With most of the metals we use, a simple heat treatment won’t do
that (some alloys might, such as many types of steel, for
example). But work hardening certainly will. If you deform the
metal, bending it back and forth, hammering/planishing it (which
thins it, of course) rolling it, or even perhaps just vigorous
burnishing of the surface, you cause deformation and distortion
of the crystal shapes. When you then anneal the metal again
(without overheating) the large distorted crystals “relax”,
breaking apart and recrystalizing as smaller crystals. The
result will again be a more fine grained material. If you did
not get actual cracking taking place in the original coarse
grained metal, then you might well be right back in business.

However, note that although coarse grained metal may give you
orange peel (caused by the size of the individual crystals making
their own distortion as you bend visible on the surface as
individual grains, rather than as just a duller look given by
many small crystals doing essentially the same thing on a tiny
scale) you may not actually have unworkable metal from large
grain size. Just LESS workable metal that may require a bit more
effort to clean up and polish once you’re done.

Peter Rowe