I know how to do this with siver (it's in the Rio catalog)-- 650
degrees for 1/2 hour-45 minutes-- but can you give details on a
couple of gold alloys? Does this work on the relatively high karat
(softer) alloys such as 18 or 22 yellow?
The procedure is similar in the gold alloys. Check the details in
the chart at the back of Alan Reviere's Professional Goldsmithing
book. Nice chart. Nice book.
It works in higher karat golds IF the alloying metals are more
copper weighted instead of the common alloys which often have more
silver than copper. With 22K, you won't get as much hardening as
with 18K, but you can get some, especially if it's a rose gold. If
the alloy is mostly silver, you won't get significant hardening. With
the 18K, likewise. If it's an 18K yellow, similar to the usual
italian yellow colors, then it may not have enough copper in it to
give you all that much hardening. But those with more copper, say
at least half copper in the copper to silver ratio, then it can be
significant. And the 18K rose golds, those with much more copper
than silver, or mostly copper, are among the alloys that give the
highest levels of hardness with heat treatment. An 18K red gold, only
copper and gold, will become so hard and brittle that dropping it on
the floor can be risky. It might shatter. In this case, part of the
hardening is not just precipitation hardening, but the formation of
an ordered array structure that one normally needs to try and avoid,
to keep the metal from being so brittle as to crack too easily.