Lab grown diamonds are becoming increasingly popular in today’s market, and as they are anywhere from 30 to 40 percent less expensive than traditionally mined diamonds, their market share is likely to grow. With the technology for creating lab grown diamonds continuing to improve, being able to differentiate between them and their traditionally mined cousins has become increasingly important.
Lab Grown Diamond Basics
Lab grown diamonds are created by one of two different processes, either High Pressure High Heat (HPHT) or Chemical Vapor Deposition (CVD). HPHT diamonds are made using artificial processes that mimic the natural heat and pressure necessary to create a naturally formed diamond. CVD diamonds are grown from a tiny diamond ‘seed’ crystal in a mixture of methane and hydrogen gases, where diamond crystals are formed in multiple, single atom layers. Both the HPHT and CVD processes result in diamonds that are chemically and optically the same as their natural counterparts. Unlike diamond simulants like moissanite and cubic zirconia that can be easily distinguished by trained gemologists, lab grown diamonds are much harder to differentiate.
Laser Inscription on Lab Grown Diamonds
The easiest way for a lab grown diamond to be identified is when it declares its own origin with a laser inscription. The Gemological Institute of America issues grading reports for diamonds based on the traditional 4 Cs (color, clarity, cut, and carat weight), and when they grade a synthetic diamond, they laser etch the diamond on its girdle with the report number and a statement that the diamond is lab grown.
Many reputable manufacturers of lab grown diamonds will etch the girdle of their stones as well to avoid any possibility of deception. This small etching is only visible under magnification, and in no way compromises the stone’s appearance.
Diamonds are classified into two main categories, type I and type II, based on their differences in transparency under ultraviolet radiation. Two subcategories for each type indicate the arrangement of the carbon atoms and impurities within the crystal.
Type Ia diamonds make up the vast majority of natural diamonds, and contain plentiful clusters or pairs of nitrogen atoms. Type Ib diamonds contain only isolated nitrogen atoms, and are very rare in nature. Type IIa contains almost no nitrogen, and IIb diamonds contain boron.
Type Ia diamonds, which make up more than 95% of all naturally occurring diamonds, cannot be grown artificially, so synthetic diamonds are available only in types Ib, IIa, and IIb—all rare categories in nature.
Type I and II diamonds can be identified by their relative transparency under short-wave ultraviolet radiation, or by using infrared spectroscopy in a gemological laboratory.
Differences in Diamond Growth
Natural diamonds were formed millions, sometimes billions of years ago deep within the earth, under a range of pressure and temperature conditions. Synthetic diamonds are formed in a vastly shorter period of time, from a few weeks to a month or more, resulting in differences in the way the crystals are shaped.
HPHT synthesized diamonds typically exhibit cubic faces in addition to the more common octahedral faces, and this results in a distinct difference in their internal growth patterns. Other distinctive features of HPHT diamonds are graining patterns and uneven color distribution as a result of their unique structure. They also tend to have occasional dark flux-metal inclusions not typical of naturally formed diamonds, which are sometimes large enough to be detectable by a magnet.
Color zoning can be evident in these gems as well. Unlike the occasional color zoning in naturally occurring diamonds, HPHT synthetic diamonds sometimes exhibit a geometric pattern in their color zoning.
CVD synthesized diamonds have gemological properties that differ from HPHT grown gems. Not only are they generally of a higher clarity, with few, if any, small inclusions, but they tend to exhibit a banded “strain” type pattern when viewed between crossed polarizing filters. And unlike HPHT diamonds, CVD grown diamonds normally show even coloration.
Fluorescence in Lab Grown Diamonds
When viewed under ultraviolet light, about 30% of naturally formed diamonds exhibit fluorescence, or the tendency to emit a soft colored glow. HPHT grown diamonds often show a cross shaped fluorescence pattern on their crown or pavilion, and CVD grown diamonds can exhibit a striated pattern when observed through the pavilion facets, typically in green, yellow, orange, or red.
The Bottom Line
The real answer to the question “How can I tell if this diamond is lab grown?” is simple: without training and expensive imaging equipment, you can’t. What you can do is only buy diamonds from trusted sources. The best way to be sure about your diamond’s pedigree is to insist on its certificate from a trusted grading facility like the Gemological Institute of America.
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