Natural Boulder opal, overlays and doublets should not be thin opal
and are not good ring stones as the top layer is the fragile gem
material and no backing will provide strength for it. Triplets on
the other hand are particularly suited for this purpose.
Not all opal triplets are created equally, caps can be made of glass,
quartz or spinel, base can be glass, basalt, agate or jade, adhesive
can be super glue, epoxy or uv cured dental resin and of course the
opal itself can be cheap milk worth only a few hundred $ per oz to
the finest crystal costing several many thousands per oz. These
combinations add up to triplet availability from a few dollars each
to stones costing over $1,000 carrying guarantees from 5 yards and 5
minutes to full lifetime non separation unconditional guarantees.
I would never recommend using a triplet that had less than a lifetime
guarantee any more than I would consider selling one without such
warranty and without a full assurance that the stone is ultrasonic
Anthony L. Lloyd-Rees