1. I don't have access to a kiln, and my kitchen oven goes up to
550 degrees F. Is this close enough to the desired temperature to
afford me some degree of hardening?
Possibly. Precipitation hardening is not a process that absolutely
requires a specific temp. The usually given temps are where it’s
fastest and most efficient. However, 550 F is a quite considerable
distance from the desired range. I suspect that you’ll not get full
hardening, and may not get all that much. If you do get hardening, it
certainly will require more time than is normally used. I’d imagine
you’ll have to experiment a bit to see whether it works and how long
to leave it in for. And one other thought. Your oven is calibrated
to 550. But what about, if there is one, the self cleaning cycle that
many ovens have? Usually, these go hotter. You’d need some "tempil"
tablets to calibrate how hot the oven gets on it’s clean cycle, to be
sure it’s not getting TOO hot.
2. Any need for boric acid dip to prevent "oxidation"?
Yes. But I’d suggest prips flux, or another more complex true flux
mixture, rather than just boric acid. Sterling silver is less
efficiently protected by simple boric acid, since it tends to “ball
up” and pull away from the surface. Though 550 isn’t all THAT hot,
it’s still hot enough to build up a pretty oxidized surface if you
leave your metal in there for a couple hours, which may well be what’s
3. Any concerns about color change in stones like amethyst,
topaz, etc.? Should heat hardening be done before setting stones?
As a general rule, yes. For amethyst or topaz, absolutely. This
depends a lot on what types of stones are being used. Since the
heating cycle can be done slowly, placing the work in the oven,
turning it on to heat treat and then turning it off and waiting till
it’s cool before opening, some stones will be able to withstand the
heat where they might not do so with, for example, torch heating in
normal work. Again, you’d have to experiment. But in general, heat
treat your work before setting the stones. Most of the semiprecious
and softer stones won’t like spending an hour or two at 550 or more.
But corundum, (sapphire, ruby), especially the synthetic ones, will
withstand these temps just fine.
Hope this helps.