Quench when it no longer glows red with the lights out? Dull red
or no red?
Button between glowing dark dull red in subdued light, to a little
cooler, like around 900F. Too much hotter than that and you can
crack it just from shock, too much cooler and it starts to harden,
which makes it brittle. 18K red gold, like around 75 percent gold and
25 percent copper is the really "dangerous" one that can become glass
hard and brittle if cooled too slow. With some silver in it still
(most "rose" golds still have a little silver), or 14K alloys, it's a
little less tricky. You just want to avoid a slow cool through the
700-800F temp range to avoid hardening.