ah hah - makes sense, raku coloring comes from copper! Was just
about to attempt to solder a sterling bezel to the back of an
already set (by me) irredescent raku piece. Not a good idea, I
The good news is, the raku would probably stand the heat/heat shock.
But it might very well lose its color.
On the other hand, FYI, sometimes raku pieces fail to get reduced
coming out of the original firing, and are bright copper-penny in
appearance (ghastly!) One sometimes-successful remedy is to play a
torch with a reducing flame over them to produce iridescent colors!
I wish I had one of those bright copper pieces around-- I'd try
iridescent patina on it.