David, it sounds like you have a piece of Indonesian opal. The opal
you have is one that has to be worked dry because, as you found, the
color disappears when wet, but will return when dry. When I was
still doing shows, there was a dealer who specialized in this opal.
We talked a lot about the opal and how it was worked. There is some
of the Indonesian opal that has exactly the opposite
characteristics. IE when dry, there is no color, but when fully
wet, the color appears. These are good for display but not much use
in jewelry. Both types have very good play of color, and some rival
the best of Lighting Ridge Blacks.
I have a piece of Nevada opal with the same characteristics. The
opal is prone to absorbing oils and chemicals, so cleaning with
water only is a must. As you found also, it is a very soft opal.
Care should be used in setting it, and if you attempt to re polish
it, I would recommend not using Cerium Oxide as it will acclimatize
in the porous opal and discolor it. Diamond on a fiber belt/disk
will give you the best results. When polishing a mounting, care
should be taken not to load the stone with rouge. I recommend using
a pink silicon wheel and polish just to the edge of the gold, not
onto the opal surface. This seems to work well.
I have no experience with the stability of the opal, but based on
it’s similar characteristics to some of the Nevada opal, it might
not be very stable. My dealer friend didn’t care to share this
I would be interested in hearing from others on this