Hello! I am fairly new to purchasing finished gemstones, and I received one recently that surprised me. It is an Ethiopian Opal cabochon, about 7mm x 8mm x 5mm high. The bottom is not flat, but somewhat rounded. Do you know why it would have been finished this way?
I’ll have to either flatten it or figure out how to bezel set it with some kind of filler to keep it stable in the setting…
That seems to be pretty common now. I’ve gotten some rubies and sapphires like that.
So makaturquoise, do you flatten the bottom or set them with some stabilization method?
(If I flatten it, I’m concerned about opal, which is soft and brittle…)
If I might chime in, u dont modify the stone, u build a setting to show the stone to the max. If u like ur stone why modify a touchy stone to begin with. Im posting 2 pics of my opal in a setting built by my jeweler, 18kt gold , yellow, & very well finished. Opal is rare & if u have a nice one, show it!-b careful-steve…
Yes, I agree the setting in the photo is best for your type of stone (rounded bottom) and also what I use most. If you don’t want that type of setting you can set it in a bezel with or without a backing, or one with a backing that has a hole in the center (of the back). If you set in a bezel with backing, set it in cornhusk, but don’t flatten the back under any circumstances, no matter the type of stone.
Thanks for all the input. I agree, it doesn’t seem advisable to alter the back of this finished stone! I ordered this stone for a particular project, which needs a closed back. I contacted a different seller, and am actually ordering another stone (that definitely has a perfectly flat back) for my project - so that frees up this stone to be set with prongs…
I really appreciate the input.
So yea, when purchasing cabs I also see alot of shaped bottoms. Its a accepted style. And I think it serves to highlight the beauty of the reverse side, in some ways its actually a nice touch because when the owner turns their piece to inspect their item they will be greeted with a nice shaped surprise.
One of the biggest reasons I find is weight retention. In the old days semi-precious stones were sold by dimension, weight was almost irrelevant, that is no longer the case.
It sounds like you have a double sided cabochon. The face of the stone will have (preferably) the high dome and the bottom will have a low dome. It’s intended to be mounted in a way that allows the stone to be viewed from both sides. When I was being taught how to cut Opal, all my instructors taught me to cut a 20 - 30 degree inward angle just below the girdle then perfectly flat on the bottom. The small beveled bottom allows the stone to sit perfectly into the setting unlike a completely flat bottom. None of my opals have sharp edges above of below the girdle simply because Opal is soft and those sharp edges are prone to get chipped or cracked.
I don’t know if I explained it well or not. I’ll include a picture of one my stones for an example.
Don’t touch the stone. Have a new setting made by a good designer. Ethiopian opals are fragile, will loose colors if water touches it. It is very porous. keep it in your drawer. it is not stable
I agree Mike, retention of total carat weight seems to be the driving force behind current designs. The higher the carat weight, the more can be charged for the stone.
A curved bottom to a cabochon often is a signifier of a decent quality of stone as it increases carat weight in an area that isn’t deemed absolutely necessary… a lesser quality or synthetic cabochon will more likely have a flat/ sharper sedge and back.
it is my personal opinion that the softer rounded backs on a cabochon are lovely against the skin and create settings accordingly…
