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.