By Tom and Kay Benham, Contributing Editors, Lapidary Journal Jewelry Artist
If you must bond an opal into a silver or gold setting, we suggest using a high-quality, two-part epoxy adhesive. The secret to achieving a good bond joint is (1) clean both surfaces to be bonded with alcohol to remove any oil or grease residue and (2) be certain that the epoxy is well mixed. You should mix continuously for approximately two minutes.
If the top of the opal has been scratched or marked by a Dremel®, it needs to be reground and repolished. But, if the quartz crystal cap itself has come off, then the remaining surface needs to be lightly ground using a flat lap to remove any high spots and the adhesive residue, taking care not to grind through the layer of color and fire. Then a new quartz cap should be carefully bonded to this surface, again, using high-quality, two-part epoxy.