Bangkok Gems & Jewellery Magazine


			Old issues	Vol. 18 No. 7 -- February 2005
				GIA ReleasesReport on Diamond Cut
				Reports on Lead Glass Filled Repaired Rubies

GIA Releases Report on Diamond Cut
Latest Issue of Gems & Gemology Outlines Basis for New Cut Grading System

The relationship between a round brilliant cut diamond's proportions and its appearance has been the subject of debate in the .ndustry for quite a while. Now the jemological Institute of America (GIA) puts all speculation to rest by publishing the findings of GIA Research on what makes the perfect round brilliant. The Institute's 15 fear research project has examined he intricate and complex relationships among the various actors that lead to a diamond's face-up appearance and identified he aspects that are essential to good cut quality.

The findings were published n the Fall 2004 Issue of Gems & Gemology, the Institute's award vinning publication. "A Foundation or Grading the Overall Cut Quality of Round Brilliant Cut Diamonds" by T.M. Moses et al., ties the various lements of GIA's study together ) outline the scientific basis for a diamond cut grading system.

Some of the main findings from GIA's research discussed in the article are:

• Proportions need to be considered in an interrelated manner. The combination of proportions is more important than any individual proportion value.

• Attractive diamonds can be manufactured in a wider range of proportions than would be suggested by historical practice or traditional trade perception.

These diamonds are, in generel, viewed positively by experienced members of the diamond trade, due to the overall balance of their patterns. Photos by AI Gilbertson and Barak Green. Courtesy of Gems & Gemology, @ 2004 GIA.

These diamonds are viewed negatively by experienced members of the diamond trade, due to a variety of unattractive pattern-related traits such afisheye (left), dark upper-girdle facets (centre), and a busy, interrupted overall pattern (right). Photos by Al Gilbertson and Barak sen. Courtesy of Gems & Gemology, © 2004 GIA.

• The quantity and quality of brightness (as brilliance is now called) and fire are only part of the overall diamond appearance. The pattern of bright and dark areas within a diamond (the basis of scintillation) must be considered as well.

• A thorough cut grading system needs to consider the design of a polished diamond (as evidenced by its weight and durability ratio) and its craftsmanship (as evidenced by its polish and symmetry).

• Viewing environment plays an important role in diamond appearance: to be attractive, a diamond should look good in realistic environments.
• Personal and international market preferences should be accounted for. Diamonds with different atjtjearances can be found within each cut grade, so individuals need to look at the diamond itself, not just its grade, to the one thev like best.

These two diamonds are fairly similar in diameter and face-up appearance. However, the diamond on the right contains extra, or "hidden," weight located in the thickness of the girdle; therefore, the diamond on the right would receive a lower grade in GIA's diamond cut grading system. The diamond on the left weighs 0.61 ct, while the diamond on the right weighs 0.71 ct. Photos by Al Gilbertson, Barak Green and Maha Tannous. Courtesy of Gems & Gemology, © 2004 GIA.

Result from Computer Modelling and Observation Tests.

The GIA researchers based their findings on the results of two main parts of the research project: computer modelling to predict which seis of proportions would yield the best results under specific lighting conditions; and extensive visual preference tests conducted with a wide variety of trade and non trade observers to determine the ability to consistently discern face up appearance aspects (such as durability and finish). Comparison of those results to observations of actual diamonds in similar conditions allowed the researchers to refine these metrics.Further tests evaluating overall appearance, made by representatives from all levels of the diamond trade in controlled viewing environments showed that these two aspects alone are not sufficient to predict the appearance of many diamonds.

The tests included over 70,000 observations of nearly 2,300 diamonds by more than 300 individuals. In these sessions the observers indicated their preferences in groups of two or more diamonds. The results yielded newly expanded definitions of brilliance - which is now called brightness by the GIA- and scintillation. Brightness is the appearance of white light seen when viewing a diamond face up and therefore GIA researchers prefer this term, as many people in the trade and even the general public tend to associate brilliance with other factors such as contrast as well. The article defines scintillation as: the appearance of spots of flashing light seen as the diamond, observer or light source moves (sparkle), and the relative size, arrangement and contrast of light and dark areas that result from internal and external reflection seen in a diamond when it is viewed face up while the diamond is still or moving (pattern). Typical examples of pattern related scintillation include fisheyes, dark upper girdle facets, and dark centres. The research also investigated how other quality factors - such as body colour, clarity and fluorescence - affected the relationship between a diamond's proportions and its appearance, Body colour was found to have some effect on the appearance of brightness, and some clarity characteristics were found to affect the appearance of fire, but the observers demonstrated a strong, consistent ability to disregard these effects when judging the overall diamond appearance. The viewing environment was also found to play a significant role in how a diamond looks. In addition, specific aspects of design (weight ratio and durability) and craftsmanship factors (polish and symmetry) were found to affect overall cut quality. When it is formally introduced, GIA's diamond cut grading system will consist of five grades of overall cut quality. These grades will consider seven separate components in their assessments: brightness, fire, scintillation, weight ratio, durability, polish and symmetry. To arrive at the final overall grade, each component is individually assessed and the lowest result from any of the seven components determines the final overall cut grade. The GIA says that its new diamond cut grading system will have many benefits to the trade as well as to the consumers. The comprehensive predictive system, which is based on computer modelling and human observations, will have the flexibility to accommodate most personal and international preferences. It will benefit the consumers and the trade by accommodating a larger range of proportion sets that provide pleasing, well cut diamonds. Moreover, consumers will feel more secure in using cut quality as a factor while making a buying decision with the new GIA grade and retailer will have new opportunities to educate their customers on the Fourth C. Also, by using the wider ranges for well cut diamonds identified by GIA's research, manufacturers potentially will be able lo achieve more yield from rough.
		These three diamonds demonstrate the range of face-up appearances that are possible within a single grade category in GIA's diamond cut grading system. Observation tests confirmed that personal and international preferences can cause individuals to like different diamonds within the same grade category. Photos by Al Gilbertson and Barak Green. Courtesy of Gems & Gemology, © 2004 GIA.

GIA is developing reference system software that will soon be able to provide predicted' overall cut grades based on proportion information (such as crown angle or table size) and other quality factors (such as finish) input by the user. The Institute will offer simplified versions of this software on its website free to members of the trade and consumers. More detailed versions will be available for manufacturers and there are plans to offer the software as an embedded function in optical measuring devices such as those on offer by Sarin and OGI. Versions of the software will also provide the ability to compare the results from two different proposed diamonds, view "wire frame" diamond profiles for proposed diamonds, and print the calculated results.

In the near future, GIA will incorporate the findings from its research into its education courses, various presentations, and informational brochures for the consumer and trade. The institute also plans to incorporate the results of their diamond cut research into the GIA Diamond Grading Report and GIA Diamond Dossier® for all standard round brilliant diamonds in the D-Z colour range for Flawless to 13 clarities. Each new GIA Report and Dossier® will include an overall cut grade, expanded proportion information in the form of a new diamond profile graphic, and a brief explanation of the Four Cs. GIA plans to announce their new repons in mid 2005.

:: Next