Opal fakes?

Jewelry Discussion
1

i am posting this from work, rather than my usual (home) email,
because I’m working on an article entitled “All About Opals” for
(probably) the January issue of Art Jewelry. I would like to include
a sidebar on how to spot a fake or a synthetic opal, but have not
been able to find anything on it, other than the suggestion that if
a pair matches too well, they may be man-made.

If anyone can help me out, or wants to pass on anything not widely
known that really should be included, please pass it on. If it is
not likely to be of universal interest, please email me off-forum at
noelyovo@yahoo.com. Thanks!

–Noel

Noel Yovovich
Associate Editor
Art Jewelry Magazine
21027 Crossroads Circle
P.O. Box 1612
Waukesha, WI 53187

2

Noel,

Synthetic Opal can exhibit a honeycomb effect when viewed under
magnification.

Greg DeMark
email: greg@demarkjewelry.com
Website: www.demarkjewelry.com
Custom Jewelry - Handmade Jewelry - Antique Jewelry

3

Noel, since synthetic opals are chemically physically and optically
the same as natural opal, it can be difficult to separate them.
Specific gravity, refractive index, fracture, hardness, etc., are
all the same as natural opal. The most prominent giveaway for
synthetic (Gilson) opal is viewed under magnification, and is
usually referred to as the “snakeskin,” “scale-like,” or "honeycomb"
effect. Under the microscope, synthetics have a typical honeycomb
look within individual patches of color. It also tends to have a
columnar structure when viewed from the side. I believe I have some
good examples to photograph for you if you’d like. I’ll bring my
digital camera home tomorrow in case you’d like me to send some.

Another clue is that natural black and white opal may or may not
have a white to moderate blue, green or yellow fluorescence, or none
at all under longwave UV, and it may phosphoresce (glow) for some
time after removing it from the UV light source. Synthetic opal may
or may not fluoresce moderate blue to yellow under longwave UV, but
has no phosphorescence. In a nutshell, quality synthetic opal can
fool even experienced gemologists unless they’ve examined a good
deal of natural and synthetic opal.

As for imitation, or simulated opal, the separation is usually quite
easy, especially if you’ve examined a lot of natural opal. Most
imitations are glass, plastic or epoxy based, and magnification
often shows them to have gas bubbles. The imitation glass varieties
bear a superficial resemblance to natural opal. Its RI is generally
1.50 - 1.52, but may vary. The “play-of-color” often resembles
cellophane or tinsel. SG is typically 2.41 - 2.50, but can vary.
Hardness is 5 - 6.

Plastic imitation opal can have an RI of 1.48 or as high as 1.53,
and can also show snakeskin or columnar effect, as well. It often
fluoresces strong chalky bluish-white under longwave UV, and does
not phosphoresce. SG is around 1.20 and can vary. Hardness is a
whopping 2 1/2, so light pressure with a needle will penetrate it.

I’ll take some pics of synthetics through the microscope tomorrow
and send off-list if you like, please let me know.

James S. Duncan, G.G.
James in SoFl

4 
 Synthetic Opal can exhibit a honeycomb effect when viewed under
magnification.

This is interesting! Can you expand on this? “Can” seems to suggest
that it may not. Does natural opal ever show the same pattern?
Thanks!

–Noel

5 
    Synthetic Opal can exhibit a honeycomb effect when viewed

under magnification.

This is interesting! Can you expand on this? "Can" seems to suggest
that it may not. Does natural opal ever show the same pattern?
Thanks!

You’re welcome, Noel. Yes, “can” does suggest that it may not. Some
batches of synthetic opal can be very convincing. As for natural
opal, I’ve yet to see one that displays the effect, but that doesn’t
mean it can’t happen. There is a naturally occurring oolitic opal
formation that can look very similar to “snakeskin” but is subtly
different. As I said, some synthetics are very difficult to separate
from natural opal.

James S. Duncan, G.G.
James in SoFl

6

Noel,

Every Gilson created Synthetic Opal that I have examined has shown a
honeycomb effect.

Genuine Opal never shows this effect and Imitation Opal never shows
this effect.

Imitation Opal (often referred to as floating Opal ) is either a
glass or plastic and will generally have various color foil embedded
in it.

Greg DeMark
email: greg@demarkjewelry.com
Website: www.demarkjewelry.com
Custom Jewelry - Handmade Jewelry - Antique Jewelry

7

What is the Gilson synthetic opal made from? I thought it was made
from Pyrex.

Kay

8

Continue from:

    What is the Gilson synthetic opal made from? I thought it was
made from Pyrex.

Kay, Gilson synthetic opal is made from essentially the same
minerals as natural opal and its’ chemical composition is identical;
SiO2nH2O. Some simulated (or as many say, substitute, or even fake)
opal is made from glass (most commonly, Slocum stone) that may
indeed be Pyrex, but it is not a true synthetic, like Gilson.

The glass opal simulants have a bright play-of-color that can appear
like foil, but I don’t believe it is. The areas of color become
translucent to transparent when light is transmitted from behind
them. I’ve just taken some photos of some of the characteristics of
synthetic and simulated opal for one Orchid subscriber. I may
request to post them on Ganoksin soon.

James S. Duncan, G.G.
James in SoFl

9

What is the Gilson synthetic opal made from? I thought it was made
from Pyrex.

you may be thinking of something like “Slocum” imitation opal, which
has no water content in it’s makeup and therefor more closely
resembles a glass. Whether pyrex or not, I can’t say. But Gilson is a
true synthetic.That means it’s structure and chemical composition is
similar to that of natural opal. That means it’s a structure made of
multiple spheres of amorphous silica, with water bound to the small
gaps between adjacent spheres. Play of color is due to interference
effects, like what happens with a diffraction grating, caused by the
multiple layers of evenly sized spheres. Just like natural opal.
Large scale structural differences, such as the “honeycomb” effect,
are due more to the growth process and environment differing in
nature, and no doubt speed, from the natural growth process. But
silica gel spheres are not pyrex glass, even though there is
certainly a chemical similarity, as there is with crystaline quartz
too.

Peter

10

Thanks for your in-depth explanation Peter. Based on that, I’m not
really sure what I have. Some years ago when I was at the
University, a gem salesperson visited the Univ. and, as always,
offered gems of “supposedly high quality” to the students at a
discounted price. And at that time, I bought two Gilson Opals (I
thought that was what they were). They are lovely, but perhaps I need
to take them to a gemologist and have them identified. Perhaps they
are not what I think they are.

Kay

11 
Some simulated (or as many say, substitute, or even fake) opal is
made from glass (most commonly, Slocum stone) that may indeed be
Pyrex, but it is not a true synthetic, like Gilson

Thanks James - as I told Peter, I’ll take my “Gilson Opals” (at
least I thought that was what I had) to a gemologist and get them
properly ID’d. Perhaps I have simulants rather than synthetics. In
any case, they are quite vibrant and lovely. And some day I’ll get
around to setting them, no matter what they are.

Kay

12

Continue from:

I'll take my "Gilson Opals" (at least I thought that was what I
had) to a gemologist and get them properly ID'd. Perhaps I have
simulants rather than synthetics. In any case, they are quite
vibrant and lovely. And some day I'll get around to setting them,
no matter what they are.

Hmmmm… How bout ‘sugar water (term I like)’ opal… how should it
be considered in the evaluation of opal… same process as black
onyx is done today… add sugar water, boil, add acid, walha!!,
black matrix opal… from mine run opal…Never tried it but was
made a very nice offer to set up a shop and 'run some off!.

Jim

13

Continue from:

Its pretty easy to tell Gilson Opal from the other plastic kind.
Stick it with a hot pin.

I can use Gilson Opal in my glass beads, which are at a temperature
of over 1500 degrees F. I embed chips of Gilson in glass pendants.
The other kind goes up in smoke.

I was at an InterGem show in Dallas, and the dealer of the simulant
Opal absolutely guaranteed me his Opal would hold up as well as
Gilson. He gave me a few pieces to test. I am sure he actually
believed it would hold up as well as the Gilson. I went home and put
the pieces in a glass pendant, and they went up in smoke just getting
near the hot glass. He was very apologetic when I returned and showed
him the diference.

Not to say there isnt a place in the jewelry world for the simulant.
It is quite beautiful.

You never know what you are going to get when you buy triplets.
Could be Opal, Gilson, or Simulant under the Quartz cap. When we were
in class at William Holland, studying Opal Cutting and making
doublets and triplets, I took a piece of the opalescent ribbon used
to wrap gifts. You can find it in any gift store. I glued it to a
balsite backing, put on a quartz cap, shaped and pokished it, and it
was the best looking ‘Opal’ in the show. It is the one everyone
wanted to buy…

Love and God Bless
-randy