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The last issue of Gem Market News featured an historical outline of
moissanite, along with methods of detection. Since then, the detection methods have grown
as laboratories and independents continue testing. While the introduction of any new
synthetic or imitation diamond is sure to push the panic button, we now have enough
information to assure jewelers that moissanite poses little threat to the diamond
industry. Identification without instruments is easy, and for most there should be no need
to purchase additional equipment for their store.
The Testers
When moissanite first hit the market, many jewelers rushed to purchase
testing equipment. Since diamond testers do not identify moissanite, the need for a second
tester arose. However, the early moissanite detectors that sold for around $600 were not
always accurate in their identification. Other companies quickly manufactured testers to
compete for the expected boom in sales. Although prices of the testers started coming
down, the accuracy of these early prototypes was in serious question. Occasionally, they
made mistakes and who could afford even one mistake? Now, some newer models are claiming
100% accuracy. Those in the market for a tester should check the claims of each
manufacturer. The Ceres model sells for $349 and the C3 model sells for $500. New testers
at lower prices are expected to be available soon. Therefore, you should shop around
before making a purchase of a tester.
The real question however, is whether a jeweler needs a moissanite
tester. So far, the separation is easy using a variety of methods. Our eyes hold the key
to much gemological information and too often we rely on the crutches of unnecessary
equipment. Not that equipment isn’t needed in a laboratory. No lab is complete
without a microscope, refractometer, measuring devices, and many other items. This is
simply a case where the tester has limited need.
Visual Observations
 A
review of the last article details some characteristics to look for under magnification.
Looking through the bezel facet at a slight angle, facet doubling is obvious. Although
this may be more difficult to see in shapes other than round, the current production is
round only. Other shapes have been test-marketed, so seeing a different shape in the
market is possible but still rare. Currently C3 is cutting all moissanite with a polished
girdle as opposed to a rough or faceted girdle, which is more common on a diamond. White
needle-like inclusions may be visible but this characteristic is helpful only as an
indication since similar looking inclusions occur naturally in diamond.
Other characteristics to consider include facet junctions that are not
as sharp and scintillation that is more colorful than diamond. C3 currently produces moissanite in the J-N
color range, possibly with a slight greenish tint. The company has been attempting to
modify the process to produce higher colors. At this time we have no knowledge of any
success.
After the article appeared in our last issue, several subscribers called
or e-mailed to convey their own experiences with moissanite. One such contact came from
Nancy Stacy who gave us another trick to locating the doubling of moissanite. Using a
microscope, focus the depth of field so that the culet is in sharp focus when viewing the
stone perpendicular through the table. Then, adjust the focus to just below the culet and
the doubling will jump out all over. The magnification techniques are so simple that most
jewelers should not need testing equipment.
 Another
identification trick comes from R. B. Grampp, Bluestone Trading, who supplied his visual
techniques for the last article. When moissanite is heated slightly, the material will
turn green. To do this test, take a match and apply heat from the flame directly on the
stone. Move the match slowly back and forth under the stone. Too much direct heat will
leave a black carbon residue on the stone but that can be cleaned. If it is moissanite, it
will take on a greenish appearance that is obvious to the naked eye.
Alan Hodgkinson, of Visual Optics fame and a noted gemologist in
Scotland,  recently
shared his visual optics techniques for identifying moissanite. His first method involves
the visual optics method of holding the moissanite up to the eye while looking at a light
source. A vision of ‘primaries’ and ‘secondaries’1 will appear in a
pattern distinctly different from that of diamond. This method is simple, takes only a few
minutes to learn, a few seconds to perform, and works with mounted and unmounted
moissanites.
Hodgkinson took his technique one step further by developing a test for
parcels of melee.
This was an obvious concern for diamond dealers who routinely purchase large diamond
parcels. If they salted the parcels with moissanite, individual testing would take too
much time. Briefly, the test is as follows. Pour the parcel into a plastic lid and cover
the stones with water. Hold the lid over white paper. Using a fibre optic light or a
flashlight, shine the light down over the stones reflecting onto the white paper below.
Move the tray and use a tweezers to move the stones around so that all have the
opportunity to be reflected onto the paper. The diamonds and the moissanites will give
distinctly different patterns on the paper making it easy to pull out any moissanite from
the parcel.
Hodgkinson also added another heat method besides the match. Using a hot
plate and a 250-watt light bulb, the stones begin to heat up. Any moissanite present will
turn a bright yellow.
Growth Tubes
While analyzing some samples,  I noticed what at first appeared to be a
laser drill hole in the table of the moissanite running perpendicular to the stone. When I
asked C3 about this, I discovered that this was in fact a growth tube. The company
acknowledged that the appearance of these tubes can be mistaken for a laser drill hole.
The tubes, when present, are an unavoidable part of the growth process. It seems that
something (perhaps a small impurity) causes a void to form inside the stone. The growth
continues but the void also continues right up to the surface. The result is a growth tube
that is perpendicular to the table (parallel to the c-axis).
I have a theory that currently remains unproven but worth sharing. One characteristic of
moissanite is the needle-like inclusions seen in some stones. Other moissanites are very
clean internally. However, I believe that at higher magnification, some needles will be
present and in fact these needles are all growth tubes. I speculate that microscopic
impurities cause these growth tubes, which are always perpendicular to the table (parallel
to the c-axis as they are currently cut). Because of the high refractive properties, the
needles usually appear to be going in different directions and often appear to radiate
from the center to the outer edges. However, from personal observation, I believe that
these needles are all the same direction, and are microscopic tubes that only appear as
tubes when magnified beyond 90X. If an impurity appears during the growth process that is
larger than normal, the tube becomes visible even as low as 10X, thus the lasered
look-a-like.
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1 In his book Visual Optics, Alan Hodgkinson describes primaries and
secondaries. The primary and secondary images result in spectral patterns seen in
gemstones with the unaided eye when viewed through the table and looking at a light
source.
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