There latest diamond stimulant is synthetic monissanite. Although there have been reports of monissanite being produced in Russia since the mid 1990s, it wasn’t unitl 1998 that there was a significant commercial production by Cree Research in the USA with marketing by the then C3 Corporation and now Charles & Colvard. It has been mainly marketed as a new jewel but also as a diamond of equivalent quality. However, it is an expensive fake costing 20 times more than CZ. It now appears in mixed diamond and moissanite jewelry and loose stones are being sold fraudulently in mixed diamond parcels.
Moissanite is a diamond simulant. It should not be difficult for someone, who knows what to look for, to distinguish moissanite from diamond as it has a number of different properties:
– Moissanite, unlike diamond, is doubly refractive.
– It often has needle like inclusions.
– It has a different specific gravity to diamond (3.22 v 3.52 for diamond).
– Its appearance/brilliance is different to diamond. Moissanite often has a greenish/yellow appearance and the color is currently below H.
– Diamond is three times harder than moissanite.
– It is reported that, if heated on a hot plate for a few seconds, moissanite will briefly turn yellow.
– Majority of moissanite are inert under ultraviolet light i.e. they do not fluorscence (rarely will they exhibit a weak orange fluorescence under Long wave and Short wave). Most diamonds exhibit varying strengths of fluorescence. However, this should not be used as diagnostic test.
In March 1999, Pegasus Overseas Ltd. In Antwerp, a subsidiary of Lazare Kaplan (LKI), announced they were to begin marketing polished diamonds treated by General Electric (GE) to improve their color, using equipment similar to that used to produce synthetic diamonds. The treatment, which can only be applied to a very small percentage (much less than 1%) of rare, brown Type IIa diamonds, involves using High Pressure, High Temperature (HPHT) conditions to transform them to colorless or near colorless.
A small number of other manufacturers are also rumored to be decolorising (treating) brown type IIa diamonds in this way. GE/LKI HPHT treated diamonds are currently being marketed using the GE brand name “BellataireTM”. All stones are graded by the Gemmological Institute of America (GIA) and are laser inscribed with the BellataireTM logo, “GE POL” and a serial number on the girdle. The GIA grading certificate indicates that the stone has undergone a GE process to change the color.
HPHT treated diamonds can only be conclusively identified in a laboratory, however, a number of distinguishing features might indicate a stone has been treated. These are brown, streaky colour zoning or graining, and cross-hatched strain patterns under crossed polarizers. The recently treated stones are IF to VVS1 in quality but some of the earlier examples contained inclusions and feathers with surrounding stress cracks. Such stones may also have cleaved during treatment, often with the presence of graphite.
There have been reported instances where the GE POL inscription has been polished off (this is deceptive practice and is a breach of WFDB rules) and the stones have been re-submitted to the GIA and HRD for certifying. Therefore, a girdle without inscription does not indicate that a stone is natural.
Most BellataireTM stones are fancy shapes, between 1 carat and 2 carats in size and D to G in colour. Some stones of over 15 carats exist.
The possibility of the fraudulent removal of the laser inscription from some GE POL diamonds and the passing off as natural of other HPHT treated type IIa diamonds, unfortunately makes it necessary to screen every polished type IIa diamond for potential HPHT treatment. A number of major gem testing laboratories have the knowledge and technical ability to provide this service. It should be remembered that technical ability to provide this service. It should be remembered that type IIa diamonds comprise less than 1% of all diamonds and of these only a fraction are capable of surviving the HPHT treatment.
HPHT Color Changed Diamonds
Several companies, including NovaDiamond and BellataireTM use a HPHT process to convert brown type I diamonds to vivid yellow-green. Natural vivid yellow-green diamonds are exceptionally rare. Nova Diamonds are certified by the European Gem Trade Laboratory (EGL) in New York and are laser inscribed with the NovaDiamond logo and a serial number. Similarly, BellataireTM diamonds of this type will be laser inscribed “GE POL” and accompanied by a certificate from the GIA.
HPHT greenish yellow diamonds show several identifying characteristics;
– Highly saturated body color
– Internal brown to yellow octahedral graining
– Tension cracks around crystalline inclusions
– The stones exhibit an intense chalky greenish yellow to yellow-green fluorescence under long wave and short wave ultraviolet light
Distinctive features seen in combination using a hand held spectroscope; a line at 415nm, a strong band from about 480 to 500nm, a strong line at 503nm, and emission lines at 505 and 515nm.
HPHT treated yellow-green diamonds can be identified if submitted to a reputable gemological laboratory.
Diamonds can be treated using irradiation and subsequent heat-treatment, if necessary, to produce green, yellow, blue, pink, and brown colors. The two modern methods of irradiation are:
Electron irradiation – using high-energy electrons from a charged particle accelerator. This does not carry the risk of radioactivity.
Neutron irradiation – using fast neutrons from a nuclear reactor. This potential, but rarely, carries a risk of radioactivity.
Electron irradiated stones are usually a distinctive greenish-blue color, and exhibit “umbrella” colour zoning, randomly scattered dark patches, or a dark ring effect upon examination.