The following is a press release from the Gemological Institute of America
(GIA). It was received by Rapaport News on Tuesday November 30.
GIA on
Diamond Cut: Latest Gems & Gemology Article Outlines Basis for New Cut
Grading System
By GIA Research
Carlsbad, Calif. – Nov. 18, 2004 –
Issues regarding diamond cut, particularly the relationship between a round
brilliant’s proportions and its appearance, have captured the attention of many
in our industry during the last decade. Although some believe that only certain
narrow proportion parameters yield the best appearance, cut has remained the
least understood element of diamond quality. During this time, the Gemological
Institute of America (GIA) has worked to determine what it takes to produce an
attractive, lively diamond. The Institute’s 15 year research project has
examined the intricate and complex relationships among the various factors that
lead to a diamond’s face-up appearance and identified the aspects that are
essential to good cut quality.
The article in the Fall 2004 issue of Gems
& Gemology, “A Foundation for Grading the Overall Cut Quality of Round
Brilliant Cut Diamonds” by T. M. Moses et al., ties the various elements of
GIA’s study together to outline the scientific basis for a diamond cut grading
system. The key results of this study bring to fruition the previous GIA reports
on brilliance (in the Fall 1998 Gems & Gemology) and fire (in the Fall 2001
Gems & Gemology). Some of the main findings from GIA’s research discussed in
the new 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.
• The quantity and quality of brightness (as
brilliance is now called) and fire are only part of 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
ratio and durability) 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 appearances can be found within each cut
grade, so individuals need to look at the diamond itself, not just its grade, to
choose the one they like best.
Results From Computer Modeling and
Observation Tests
The GIA researchers based their findings on the results
of the two main parts of the research project: computer modeling to predict
which sets 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 (brightness, fire, and scintillation) and the
importance of other cut quality components (such as durability and
finish).
The results of the preliminary computer modeling for brilliance
and fire were reported in Gems & Gemology. Comparison of those results to
observations of actual diamonds in similar conditions allowed the researchers to
refine these metrics. Further observation tests evaluating overall appearance,
made by representatives from all levels of the diamond trade in controlled
viewing environments, also confirmed that those two aspects alone were
insufficient to predict the appearance of many diamonds.
“Our initial
observation tests revealed that, as we expected, our best brightness and fire
metrics were able to predict specific observation results (i.e., brightness and
fire), but they were not adequate to predict and evaluate a diamond’s overall
cut appearance and quality,” wrote Moses and his colleagues.
These tests
included over 70,000 observations of nearly 2,300 diamonds by more than 300
individuals. In these sessions, observers indicated their preferences in groups
of two or more diamonds. The results yielded newly expanded definitions of
brilliance—now called brightness by GIA—and scintillation.
Brightness is
the appearance of white light seen when viewing a diamond face-up (this includes
the effects of direct reflections—or glare). The researchers preferred to use
the term brightness (over brilliance) because many individuals in the trade and
general public associate brilliance with other appearance factors (such as
contrast).
In the new article, scintillation is defined as: (1) the
appearance of spots of flashing light seen as the diamond, observer or light
source moves (sparkle), and (2) the relative size, arrangement and contrast of
bright and dark areas that result from internal and external reflections seen in
a diamond when it is viewed face-up, while that diamond is still or moving
(pattern). Typical examples of pattern-related scintillation include fisheyes,
dark upper girdle facets, and dark centers.
The viewing environment
(whether in a dealer’s office, retail store, or the many places in which a
diamond is worn by a consumer) was found to play a significant role in how a
diamond looks. To facilitate consistent observations of cut appearance, the
researchers developed a standard lighting environment, consisting of a neutral
grey box lit by diffuse lighting (for brightness) and directed “spot” lighting
(for fire). The research demonstrated that observations made in this environment
yielded the same relative ordering of a set of test diamonds as the observations
made in typical trade environments.
The researchers also investigated how
other quality factors—such as body color, clarity, and fluorescence—affected the
relationship between a diamond’s proportions and its appearance. Body color was
found to have some effect on the appearance of brightness, and some clarity
characteristics were found to affect the appearance of fire, but observers
demonstrated a strong, consistent ability to disregard these effects when
judging overall diamond appearance.
In addition, specific aspects of design
(weight ratio and durability) and craftsmanship factors (polish and symmetry)
were found to affect overall cut quality.
GIA’s diamond cut grading
system, when introduced, will consist of five grades for 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.
---Benefits of GIA Grading System
The
result of this research is a comprehensive predictive system, based on computer
modeling and human observations, which has the flexibility to accommodate most
personal and international preferences.
The new GIA diamond cut grading
system will benefit consumers and the trade by accommodating a larger range of
proportion sets that provide pleasing, well-cut diamonds.
Consumers will
feel more secure in using cut quality as a factor when making buying decisions
(much like they currently use the other three Cs of color, clarity and carat
weight) with the new GIA cut grade.
Retailers will benefit from GIA’s new
diamond cut grading system. In addition to the availability of a broader range
of diamond proportions that are considered well-cut, they will have new
opportunities (and a system that supports those opportunities) to educate their
customers on the Fourth C.
Manufacturers also will benefit from GIA’s new
diamond cut grading system. By using the wider ranges for well-cut diamonds
identified by GIA’s research, manufacturers potentially will be able to achieve
more yield from rough.
---GIA Software and Grading Reports
To aid
all levels of the diamond trade, including manufacturers, retailers and
appraisers, GIA is developing reference system software that will soon be
available 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.
GIA intends to provide simplified versions
of this software (which will be available on the GIA website) free to consumers
and members of the diamond trade. More detailed versions will also be available
for those involved in diamond manufacturing. In addition, GIA plans to offer the
software as an embedded function in optical measuring devices (such as those
offered 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
color range for Flawless to I3 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 reports in mid 2005.
Articles cited above are
available at
http://www.gia.edu/gemsandgemology/27540/free_article_downloads.cfm.
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