GIA publishes observations on CVD Lab-grown diamonds

CVD
[Image Courtesy: Pittsburgh Post-Gazette]

During last decade, advancement of Lab-grown diamonds (often incorrectly termed as synthetics) rose phenomenally and its perceived value is also going up. While Lab-grown diamonds are estimated to control 95% of the industrial applications of diamonds, they are also being increasingly taken up for Gem and Jewelry usage. GIA (Gemological Institute of America) recently published a report on CVD Lab-grown diamonds.

Lab–grown diamonds grown using HPHT (High Pressure-High Temperature) technique are commercially available since early 1990s. However, Lab-grown diamonds grown using CVD (Chemical Vapor Deposition) technique has emerged only in recent few years. Hence, GIA published a report that includes ‘statistical data and distinctive identification features’ by reviewing data of CVD Lab-grown diamonds examined by it from 2003 to June 2016. Observations made by them are limited to gem-quality materials only.

2003 – 2008 was a ‘pre-commercial’ era for CVD diamonds, during which though many advances took place, the product was in developmental stage and it was rarely available to public. From 2008, the product improved in terms of color and quality and went into commercial production. The report says that, due to this reason, 75% of the samples surveyed for this review date 2013 or later. The sample set received by GIA is itself a very small portion of the trade.

The analysis focuses on two categories of material. First category involves diamonds falling in D – N color range (Colorless – near colorless – very light brown), collectively referred to as ‘near colorless’ and which are generally low nitrogen Type IIa. Second category consists of Type IIa ‘Pink’ samples. The report summarizes quality factors, gemological properties, UV fluorescence reactions and key special features of these two categories. Observations such as short-wave fluorescence, near-infrared absorption spectroscopy are not discussed in the report.

Carat weight

Though most of the samples of 2003 – 2008 period were of 0.5 carat and below, in recent few years the trend has changed. In the Jan – June 2016 samples, close to 50% of the diamonds weighed more than 1 carat.

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[Image Courtesy: GIA]
“Figure 4. The carat weight distribution of CVD synthetic diamonds analyzed by GIA from 2003 through September 2016. In the “pre-commercial” era (2003–2008), the samples were donated or loaned to GIA by manufacturers. In later years, the samples were a mixture of donated samples and those submitted by clients. The years 2010 and 2011 are combined because of the decrease in production that resulted when a major manufacturer, Apollo, was acquired by Scio. This chart clearly illustrates the increasing size of CVD synthetic diamonds in the marketplace.”

Cut

83% of the CVD diamond samples were of round brilliant cut. In other styles, 3% were rectangle, 3% cut-cornered rectangle and 4% emerald cut. Popularity of round brilliant cut is the reason behind manufacturers choosing facet pertaining to that cut despite the fact that other shapes retain more weight from original rough. When round brilliant cut CVD diamonds are compared to their mined counterparts, 85% have excellent cut.

Color

Most of CVD diamond samples fell in ‘near-colorless’ category. 67% were in G – J range, 21% in D – F range, 10% in K – N range and 1% in split-grade range. Certain CVD diamond samples examined by GIA were of colors other than pink such as Fancy color brown, fancy color yellow, blue. They, according to GIA were not commercially important.

Clarity

Though most of CVD diamond samples surveyed received VVS2 / VS1 range, they did cover the entire clarity span. Though many different grade-setting clarity characteristics were found in these samples, none of them were helpful in identification purpose. Hence graders have to use the same clarity terminologies for CVD Lab-grown diamonds and mined diamonds.

Identification

Besides, the report mentions that “most CVD manufacturers inscribe their products as laboratory-grown on the girdle, as in this photo. Similarly, all samples identified as synthetic diamonds leave GIA with an identifying inscription of ‘Laboratory Grown.’ “, making identification of CVD Lab-grown diamonds easy.

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[Image Courtesy: GIA, Sally-Eaton-Magana]

The report also mentions that many features observed in early CVD diamonds are less relevant in present scenario and this trend will persist in future. The quality, cut and clarity have been consistent in CVD Lab-grown diamonds but the carat weight has risen.

 

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