Experienced Jewellers and Gemologists should have little need for diamond testers and moissanite testers, assuming experience and practice in Testing for Moissanite.
Moissanite testers must be considered essential:
Moissanite should retail from 5% to 10% of the cost of a natural diamond.
Purchasing a moissanite in the belief that it is a diamond would be an embarrassing and costly mistake. CBC Market Place investigated the susceptibility of professionals to moissanite scams: Market Place Files - Moissanite
The following tests are presented in no particular order. Some methods may only be used for loose stones, some are most suitable for quickly testing a parcel of stones, and some may damage diamond simulants:
No single test
should be relied upon to discriminate moissanite from natural diamond.
Moissanite is doubly refractive; diamond is not. Some samples of moissanite have been reportedly cut on an axis which minimizes the doubling effect.
Because of its anisotropic optical character, moissanite exhibits double refraction depending on the orientation in which a sample is examined. Doubling of the back facets is readily apparent, even with a simple 10X loupe.
Do not examine
by viewing the stone through the table facet.
(Adapted from CBC Website)
Inclusions, Bearding, Facets and Girdles
Some moissanite samples (but not all) have unique inclusions under magnification, which are not found in diamonds. The most common inclusions are white-appearing needles that are sub-parallel to one another and typically oriented nearly perpendicular to the table. Although these could be confused with laser drill holes in diamond, their presence indicates that further examination is required to determine if the stone is moissanite.
Under magnification, moissanite does not exhibit "bearding" or "naturals." Bearding, minute fissures in a diamond's girdle, occur in the cutting process. Naturals are growth characteristics in a diamond. The absence of bearding and naturals does not separate moissanite from other diamond simulants, and not all diamonds exhibit bearding.
Facet junctions of moissanite are not as sharp as diamond, and a moissanite's girdle is not polished as smooth as a diamond's. The girdles of most moissanites are frosted or striated, similar to those of some cubic zirconia.
Hundreds of diamonds can be screened for moissanite in minutes with this light method.
Pour a diamond parcel into a plastic lid, cover with water, and support the plastic lid 1 inch above a sheet of white paper. Hold a flashlight about 6 inches above the lid, and work in a darkened room (best results are achieved when the light is covered with a slit disc). Move the lid from side to side under the light. It does not matter whether the stones lie table facet down or pavilion down.
Trawl tweezers through the stones and pick out the moissanites by their technicolour images. The following pictures show the typical light images cast by diamonds, moissanites and cubic zirconia. Moissanite has a Refractive Index of 2.7, diamond 2.4 and cubic zirconium 2.2.
Specific Gravity is the ratio of the density of a material to the density of distilled water.
Diamond has a specific gravity of 3.52. Moissanite has specific gravities between 3.17 to 3.24 (moissanite is lighter than diamond). In a liquid of the appropriate specific gravity, diamond and cubic zirconia will sink and moissanite will float.
Methylene Iodine has a specific gravity of about 3.3 and may be used to quickly check a loose parcel of stones for moissanite. Methylene Iodine is hazardous and the cautions shown on the label must be exercised.
Moissanite has a hardness of about 9.25 on the Mohs Scale, diamond has a hardness of 10. Diamond-tipped probes can scratch moissanite, but this is obviously a destructive test which may not be desirable.
A hotplate or flame may be used to discriminate moissanite from natural diamond.
Heat a diamond scoop on a hotplate or 250 watt bulb. Scoop up some stones and return the scoop to the heat. The moissanite stones will turn bright yellow within seconds and the diamonds will retain their original colour. Viewing is aided by a white overhead light. A rare diamond thermoluminescence colour change due to heat is never yellow. Moissanite turns bright yellow from about 230ºC until cool. The intensity of the colour change can vary and the visibility level of inclusions may be raised.
Cautions for the Heat Method:
Most moissanites have tinges of yellow, green, or gray. Moissanite producers have been working hard to eliminate them with some success. Completely colorless moissanite is extremely rare (for now), although larger size stones (greater than about a half carat) have less visible shading.
Conventional diamond testers, such as the Ceres CZeckpoint Diamond Tester, test for thermal conductivity and are useful in separating diamond from simulants such as cubic zirconia, corundum, glass, synthetic rutile, and zircon. Thermal diamond testers cannot be used to discriminate diamond from moissanite, because both are thermally conductive.
An electrical conductivity tester, such as the MT2 Moissanite Terminator, will indicate moissanite and would ideally be used after a thermal diamond tester has eliminated other simulants.
The two primary references used for this webpage were:
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