I have cut and set many hundreds of opals of all kinds: solids,
doublets, and triplets. Since lots ot others have weighed in on this
topic I’d also like to make a few observations. First, terminology.
An opal “solid” or “natural” is ONE piece – 100% opal. A doublet is
TWO pieces, an opal layer of variable thickness adhered to a backing
material with a durable adhesive like epoxy. A triplet is THREE
pieces, involving a black backing piece, a very thin slice of opal,
and a transparent cap. So don’t ask a supplier for a “doublet” when
what you have in mind is a triplet. (I am leaving out boulder opal
here for simplicity, but there are boulder opal doublets as well and
boulder opal “solids” aren’t 100% opal.).
The reasons for making doublets and triplets is simple. There is no
great conspiracy to defraud or mislead the buying public. Opal is
rare stuff and some lovely pieces are too thin to cut into solids. To
put their beauty on display it’s necessary to create an assembled
stone thick enough for setting. If there’s any skulduggery, it comes
in marketing. When I make a jewelry piece with a doublet I use an
open-back setting so the backing material on the stone shows clearly.
I point it out to the buyer, explain what a doublet is, and let them
know that a solid opal of the same quality would cost many times the
price of the doublet. (Re: boulder opal doublets, I believe
fraudulent intent may be more of a factor with these, but that’s
another discussion).
As a buyer, always be a little cautious when a beautiful opal is
presented in a closed-back setting. But remember it’s easy to mistake
a solid stone for a doublet as well, so study the stone carefully.
Some opals are cut as “natural doublets” i.e., the rough has a layer
of bright precious opal atop a backing of non-precious potch (of
whatever base color). It is cut as one stone but only the potch shows
through the bottom of the setting. Such stones are less valuable than
opals with skin-to-skin play of color, but much more valuable than
assembled doublets.
Doublet valuation is pretty straightforward. First, they should be
sold by the “piece,” never by carat weight. Two other important
factors are the quality of the opal and the percentage of opal to
backing. Some doublets have a very thin layer of opal on some sort of
black backing like basanite or black “onyx,” while some I have seen
are up to 80+% opal. Fine doublets can cost many hundreds of dollars
depending on size and quality. They should not be ignored by artisans
because they can provide beautiful stones with price points far below
those for comparable solids.
Properly made, a doublet is as suitable for a ring as a solid opal.
The real question is whether opal is a suitable ringstone. I have
customers who brag about wearing their jewelry 24/7 and being "rough"
on their jewelry. I try to steer them to stones that suit their
lifestyles – but not opal! (Pink tourmaline and synthetic corundum
are alternate October birthstones!) I have many customers who
understand opal’s special needs and do fine with opal jewelry. But
when I’m designing a piece – even pendants – for a solid or doublet
I try to create goldwork that will offer it some protection from sharp
bumps and knocks. The truth is, opal is fragile. But no more so than
many other popular jewelry stones like pearls or Tanzanite.
I prefer to use black opal potch as the backing for my doublets for a
simple reason. Since both layers are opal, they expand and contract
at the same rate under sudden temperature changes, like walking from a
70+ degree house into a sub-zero outdoor environment. This minimizes
stress on epoxy joints and perhaps prevents cracking of the opal.
Triplets are another matter. There are so many kinds of product on
the market it’s impossible to generalize. Years ago the triplets from
Australia featured very thin slices of natural opal with some sort of
black stone for a backing and quartz crystal caps. Some stones like
that may be produced today but the majority are made with black glass
backing and glass caps, similar to Pyrex. The only caps available to
the amateur lapidary market today are glass. (I either cut my own from
optical-grade quartz or use calibrated quartz caps from a 1970s-era
hoard). Australian triplets can be very beatiful but they ain’t what
they used to be! Triplets using laboratory-cultured opal are widely
sold by various sources, mainly Asian, and are not always identified
as such.
Opal triplets are easy to identify. Just look through stones
sideways and the clear glass or quartz area will be obvious. Some
triplets may show a little reflected play of color in the cap but they
can be easily sorted out from solids or doublets by careful naked eye
observation or 10x. Flat adhesive joints should be easily apparent
under 10x on both doublets and triplets. Triplets are the least
expensive way of enjoying the colorful impact of opal.
Triplets made from Spencer, Idaho opal can be major exceptions to
what is written above. Most of this opal can only be cut as triplets
due to the way it occurs in nature, but what triplets! It is not
widely known but triplets from this opal can yield both stars and
cat’s-eyes – the only known source in the world for these. And the
finest triplets cut from this material have absolutely no equal in my
opinion. They can be large, bright and display color patterns and
effects that as far as I can learn are not duplicated elsewhere.
These stones can be much more expensive than run-of-the-mill
Australian triplets, although there are awesome Aussie triplets too.
Idaho triplets deserve a lot more study and attention from jewelry
artisans who seek the unique.