There are only two ways to harden precious metal: work harden or air
harden. Air hardening is when you heat the metal to a specific
temperature and then let it cool - generally its not greatly
effective but is better than nothing, and it only works for certain
Work hardening works for all alloys. As the metal is deformed (or
"worked") it gets harder and harder until, unless it is annealed, it
eventually cracks or breaks. Whenever you change the shape of the
(cold) metal (bend it, twist it, hammer it, etc.) it gets harder.
Many people instinctively use this property to break a rod or piece
of wire when no tools are available - they bend it back and forth,
back and forth, until it eventually snaps.
To work harden wire, the traditional way is to twist it. Hold one
end securely, grasp the other end with pliers, and twist. To check
progress, release the pliers and "ping" the end of the wire - if its
not springy enough just continue twisting.
You can often see this effect in the pins of old broaches. After the
swivel had been soldered the wire got annealed and was too soft to
work properly as a pin, so it was twisted to work harden it. Because
the twist distorts the surface of the pin a little it increases the
friction between it and the fabric on which it is worn, thus
achieving three things: springiness, increased friction, and it it
also looks more interesting.
Another way to work harden is by bead or sand blasting. It is very
much a surface effect and, although reasonably effect for resisting
surface abrasion does little to increase the resistance to bending.
Not all alloys harden to the same extent; its no use, for example,
attempting to make a spring clasp from an alloy designed for bezels.
Regards, Gary Wooding