Greetings Dave, Re. your opal query: Basically, it's "yes" to
everything you mentioned. It all depends on the stone and what works
best with it - and safely. The play of color in
transparent/translucent opals (so called white opals) can usually be
enhanced if placed on either a black, or a white background material.
I've set opals which looked good either way and it was a subjective
choice as to which was preferable. I've set many others which looked
best on black primarily because it made the play of colors far more
If the stone in question has a yellowish tinge, then a white
background often shows that up worse than a black one. However, the
black background can cause the opal to show as grey which is usually
not attractive. When faced with this dilemma I usually try laying
the stone on the two respective colors (pieces of paper) at the bench
and see which appears best. In the case of a piece to order, you
might want to involve the customer in the decision as well.
Polishing the interior of the bezel - or matting it - usually tends
to feed the color of the metal into the stone. With white metals
this is not so much of a problem, but with gold I don't like the look
- makes the stone too yellow and mutes the color play.
As for what to use behind the stone I have a couple of suggestions.
I have pulled many opals set by jewelers unkown who used paper, or
sawdust, or who knows what, to either pad and/or enhance the color
of the stone. Anytime these came out of rings what was behind the
stone was nasty, having taken on moisture resulting in the
decomposition of the padding material.
My first choice for white is to use the file dust from a piece of
white delrin (the fellow who taught me, used sawdust from the bench
pin). The delrin makes a great cushion material, provides the
necessary white background, and is impervious to moisture. I have
used the black delrin as well, but when it is filed the resulting
filings are a definite gray, and not black. Only certain stones have
looked good with it.
I have also used very successfully both white and black silicon
rubber. If you don't want to literally glue the stone in with it you
have to find a way to place the rubber in the bezel smoothly and
allow it to set befoe setting your stone. You might try a dapping
punch or chasing tool of the appropriate size and shape. Using a
little water on the tool end helps to keep it from sticking to the
I recently set an incredibly fractured opal a customer brought me by
making a very close fitting heavy bezel and then using the silicone
rubber to "set" the stone via the glue action. This meant no
mechanical force on the stone at all, plus the added stability of the
stone being laminated to the bezel with rubber.
One can always purchase little bottles of black and white enamel
from a hobby store and literally paint the back of the stone as well.
Then you can use whatever you want for the padding material without
fear of it's affect on the color.
As for the open backs. While some stones - and finished pieces -
can be very beautifully set in this manner it does have the potential
drawbacks you mentioned, besides the increased danger to the stone in
the setting process. Most opals are not that perfectly shaped on
the back and getting a well fit seat around the edge is tough, which
makes more likely a break if stone becomes bound between the force
laying down the bezel and a minute high spot on the seat.
Except for the very brave, the latter requires the use of a thin
bezel material which I am not personally fond of. Using the heavy
bezels I do requires some cushion under the stone hence my preference
for a backing material.
Thanks for wading through this,