I knew better than that. What about heat to 1200F and allow to air
cool on a charcoal block.
1200 will fully anneal the metal. With some alloys, air cooling will
give you some age hardening as it slowly cools, but you’d get a lot
more if you heat to only about 650 F (exact temp depends on alloy)
for a half hour or so, and then allow it to slowly cool. Some alloys
will age harden almost as much as work hardening can do, though the
end strength of the result is not always the same. Some age hardened
alloys end up brittle, rather than just hard… Yellow and Rose
golds, and nickle based white golds, all can be age hardened this
But as another poster noted, you may need to stay away from white
golds for piercing rings. At least from nickle based white golds.
Nickle free ones, usually based on palladium would be Ok. But they’re
usually too soft, and they don’t age harden either.
And you might consider… There’s a reason other than just cost, why
most piercing jewelry is stainless steel, titanium, etc. They are not
only hard and springy, but hypoallergenic/inert. It’s difficult to
get both those properties at the same time with most gold alloys.
Hard usually means some level of either copper (yellow golds) or
nickle (white golds). Both, if even slightly bioavailable in the
metal, can cause problems for some people. Nickle, especially. But
with high enough karat that these aren’t a problem, then you have a
hard time getting the metal hard and springy enough to function the
way most piercing rings are made to do…
If you were going to use platinum, though, I’d suggest the SK heat
treatable platinum alloys from Hoover and Strong, or the similar HT
platinum alloys from Imperial. Both can be acceptably hardened, and
both are platinum, which is generally hypoallergenic.