With the increase in the production of synthetic diamonds for use in jewelry, there has been a vast improvement in the color and clarity of lab-created diamonds — and an increase in carat weight. Gemologists and jewelers admit that with the improvement in the quality of lab-grown diamonds, it is becoming more difficult to differentiate between these lab-produced gemstones and their natural counterparts as their chemical and physical properties are similar.
However, for the past 30 years, the Gemological Institute of America (GIA) laboratory has extensively analyzed and studied synthetic diamonds to enable them to tell them apart from natural diamonds. The GIA reports that they have only seen a small number of lab-grown diamonds submitted unknowingly for their official grading reports.
This GIA lists many of the distinctive visual features of the two kinds of synthetic diamonds:
- HPHT Synthetic CVD Synthetic
- Uneven color distribution/ even color distribution
- Graining patterns/ no graining patterns
- Unusual fluorescence colors
- Fluorescence color patterns
- Occasional phosphorescence
- Metallic flux inclusions/ occasional dark pinpoint inclusions
- No strain patterns/ banded strain patterns
- Possible inscription on girdle.
These visual features identified by the GIA are based upon the characteristics displayed by a number of these lab-grown diamonds. However, it is worth bearing in mind that — like natural diamonds — not all lab-created diamonds will display all of these features. Therefore identifying a synthetic diamond should be based on the diamond evidencing as many specified features as possible.
Synthetic diamonds made by CVD have different gemological properties than HPHT lab-created diamond material.
Lab-grown colored diamonds created using the HPHT process very often exhibit uneven coloration. This is because impurities like nitrogen or boron are incorporated into the synthetic diamond during formation. Natural diamonds occasionally show some color zoning, but this is not in the geometric pattern shown by HPHT lab-created diamonds. Color zoning in colored HPHT lab-grown diamonds relates to the different crystal faces resulting in patterns different from natural diamonds. In contrast, CVD-created synthetic diamonds typically exhibit relatively even coloration and banded strain patterns, and they are of high clarity with few, if any, slight dark carbon inclusions.
In HPHT lab-created diamonds, one can often see the inclusion of solidified flux metal. This manifests as black and opaque in transmitted light but displays an almost metallic luster in reflected light. This is caused by the flux metal alloy used to grow the lab-grown diamond containing nickel, cobalt, and iron. In fact, you can pick up synthetic diamonds with a high proportion of metallic inclusions with a magnet. Lab-grown diamonds created by CVD form differently; therefore, they do not have metallic inclusions. Some natural diamonds contain dark inclusions of graphite or another mineral, but these inclusions do not have a metallic luster.
If a natural diamond is examined between two polarizing filters placed at a 90-degree angle, it will often display a bright cross-hatched or mosaic pattern of interference or “strain” colors. This occurs because of the stresses placed upon the natural diamond while it was forming in the earth’s mantle or during its eruption to the surface. As lab-grown diamonds form in a controlled environment with no fluctuations in pressure or changes in stress levels, they exhibit no strain or weak-banded strain patterns.
The GIA has identified the major issue in the differentiation of tiny diamonds, or melee, which can include both natural and lab-created synthetic diamonds. To assist the jewelry trade in overcoming this issue, the GIA has developed an automated instrument that enables the testing of minute diamonds. As part of their ongoing research program on lab-grown diamonds, they have recently also set up a CVD growth facility where they can produce their own synthetic diamonds for study.
The best way for a consumer to find out whether a diamond is natural or lab-created is to always request a certificate upon purchasing the gemstone. You should not buy diamonds that are not accompanied by such a document. Diamond certificates (see below) issued by the GIA or IGI will indicate if the stone is a lab-grown or a natural diamond.
