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Ideal opal thickness

I’ve registered with an Australian opal auction site and I’m looking
to buy some affordable solid (NOT doublet or triplet) stones with
good colour play, both as parcels and nice individual stones. I like
the Cooper Pedy opals best. I’ve noticed that one particular seller
has some nice looking parcels in 8x6mm, 7x5mm, 6x4mm ovals, for
example. However, most of his stones are only cut at 1mm thickness,
such that they are merely slivers of opal. Instinct tells me that for
most purposes, this is too thin, especially in an 8x6 or 7x5mm stone.
I’m more inclined to buy stones in that sort of size that are at
least 2mm thick.

Am I right to avoid the 1mm thick stones? Any advice people can
offer with regard to buying opals would be much appreciated, thanks.

Helen Hill

I’ve set 1mm thick opal, but it’s a pain in the proverbial. The risk
of cracking them with a bezel set is pretty high, particularly as the
bezel wall is so low. you could back them with something, but then
they’d be doublets without the glue (insert evil smiley face here)
and still prone to cracking.

They can look beautiful when set, but it’s neither fun nor easy. In
my relatively inexperienced opinion, anyway. people with more
experience might feel differently.

Your instinct is correct. It may be that the 1mm stones are intended
to be made into doublets or triplets. If you have not previously
purchased from a dealer I would only buy in person unless you get
them on approval.


Hi Kevin,

Thanks for your advice. I have purchased some opals today from an
auction site (not ebay) and they are all returnable if I’m not
satisfied so I will send them back if not happy. I’ve had to do that
before but that was from a seller on ebay and the opals he sent me
were not the ones in the picture and they had no colour play
whatsoever. Fortunately, the ones I bought today have very good
pictures of the actual stones in question and they all have great
colour play. I’m looking forward to receiving them and setting them
into my jewellery.

Thanks again.


I have cut many an opal, mostly the Coober Pedy variety. My
favorites are from Andamooka, though. (Mine are from over 40 years
ago, and I recall that Andamooka is no longer producing like it did

Your instincts are correct- 1 mm is probably too thin. Cabs than
thin are fragile to set, damage-prone in the finished piece, and in
my opinion just look very flat, especially in the larger sizes. I cut
my cabs about 2 - 3 mm thick whenever I had the material to do so.
Since Coober Pedy opal is mostly white or light grey, I suspect that
the cutter was trying for maximum translucency in the stones rather
than end up with a dead white than tends to smother the play of

I have made a few doublets to salvage thin seams of color in a piece
of rough, and 1 mm or so was the thickness that prompted making a
doublet by cementing on a backing piece of obsidian or black jade to
provide strength and a dark background to bring out the color.
Cutting and polishing was done after the two slabs were joined.

Dick Davies

Am I right to avoid the 1mm thick stones? Any advice people can
offer with regard to buying opals would be much appreciated 

Yes, in my opinion as an opal cutter. There’s no “ideal” opal
thickness because of variables regarding gem size and profile, but
any opals only 1 mm. thick will be extremely fragile and difficult to
set. Some of the very thin stones from Coober Pedy are cut from
single color bands in white opal and yield transparent to translucent
gems. Some show color play only when contrasted against a dark
background and should be cut as doublets IMO.

Out of curiosity I measured some of my own stones and found I seldom
cut any opals, domed or flat-top, less than 2.5 mm. thick. My 5 x 7
mm. ovals average 2.5 mm. and 6 x 8’s 3 to 3.5 mm., with larger
stones up to 5 or 6 mm. in depth. Opinions will vary, of course, as
they always do on Orchid [smile].

Rick Martin


The thin slices should be cheaper if the stones are sold by weight,
so you get more flash for cash. On the other hand they are doublets
without the backing. More imortant is how they look when viewed
against the intended backround, be it skin or metal, and not sitting
on a black card for the photo.

If they have good colour without a backing then they will work well
in pendants and ear rings.

For rings they will need to be inlaid rather than set, or recessed
or protected by the setting in some way. In my opinion opals set in
rings should be set in such a way that they are easy to remove or
replace, regardless of their thickness, because they are relatively

Cheers, Alastair

Thanks to Sophie, Kevin, Richard, Rick and Alastair. You’ve given me
some hints and tips that I hadn’t thought of, so many thanks. I’ll
have to give some thought to how best to set them in a ring. I was
planning to bezel set but as far as open or closed-backed settings,
I’m not 100% sure yet.

I’ve ordered some lovely stones, one parcel and a few individual
(ring and pendant sized) stones, all Coober Pedy. I’ll have to see
what they’re like when I eventually get them via Australia’s apparent
"snail mail" (so called by an Australian, not by me). I’m hoping
I’ll get them in time to make something for Christmas! My intention
in ordering them was to remake a piece of opal jewellery for a member
of my family. I had one Coober Pedy opal from the original piece of
jewellery already (although it’s severely scratched, chipped and
dull and I’ll probably just give it back and not use it), so I was
looking for other stones to go with it or to replace it. Hopefully
I’ll have enough stones to make something for myself too! :wink:

Thanks again.