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knowledge of diamonds was incomplete. AlthoughShipley knew as much about diamonds as mostAmerican jewelers at the time, he felt embarrassedto discover that he had sold many diamonds withapparently “poor makes” — that is, diamonds thatwere cut badly. Eventually, this embarrassment,along with his desire to fully educate himself on allaspects of diamonds and other gemstones, led him toenroll in the gemology courses offered by theNational Association of Goldsmiths (London).

After his return to the United States, Shipleybegan teaching a night course in gemology at theUniversity of Southern California in Los Angeles.This course proved to be so successful that in 1931 hetransformed it into its own school: The GemologicalInstitute of America. Course material from 1936shows some of Shipley’s interests at the time. Hedevoted coursework to reviewing the differencesbetween the proper proportions of “European” and“American” styles of diamond cutting (with theAmerican cut credited mostly to Tolkowsky’s 1919publication, Diamond Design) and to describing theappearance of polished diamonds as the relationshipof two separate aspects: brilliance and fire (scintillationwould come later). At that time, Shipley wrote thatpolished diamonds showing “more vivid spectrums”possessed more brilliancy, and those that showed“wider spectrums” possessed more fire. The fact thatboth terms dealt with colored light return explainshis use of the term “spectrum.”

However, Shipley’s primary concern in thisearly course centered around his desire to identifythose diamonds of poor make. Thin (shallow) dia-monds and “lumpy” (deep) diamonds were singledout as bad light reflectors, allowing light rays toleak out of the pavilion. Similarly, Shipley singled

out shallow-topped diamonds (those with shallowcrowns and/or larger tables) as “swindled” or“spread,” and stated that they sacrificed brillianceand fire to give the appearance of a larger size. In thisway, he attempted to make up for his prior lack ofknowledge on diamond cut proportions by sharinghis newly acquired education with all of his students.

By this time, Shipley was also warning aboutdiamond merchants who were advertising “perfectdiamonds” or “perfectly cut stones.” He felt thateven if a diamond was internally “perfect” (i.e.,internally flawless), it was almost impossible for itto be “perfectly” cut. This was soon reflected in the1937 ruling by the Federal Trade Commission thatbanned the use of the term “perfect” and its variantsfor any diamond, when that term had the effect of“misleading or deceiving purchasers, prospectivepurchasers, or the consuming public.”

By 1946, Robert Shipley had also made the dis-tinction between brilliance and scintillation in hiscourse material. In response to several new “novelty”cuts on the market that were advertising greaterbrilliance, Shipley changed the course material todistinguish a separate aspect of a diamond’sappearance which he called scintillation. (Shipleysuspected the new “novelty” cuts were displayingscintillation, not brilliance.) He defined this newappearance aspect as the throwing off, or glittering,of “spark-like flashes of light.” GIA thereafter usedthree distinct aspects of light performance (brilliance,fire, and scintillation) to describe a diamond’sappearance. Shipley also introduced into the coursesthe idea of re-cutting “old style cuts” to the propor-tions of modern American cuts, and estimating their“recut” weight. This would later play a large role inGIA’s grading system.

GIA and Its History with Cut

GIA’s study of diamond cut proportions has a long history – longer, in some ways, than the historyof GIA itself, since one could say that poor cutting proportions helped motivate Robert M. Shipleyto found GIA. In the mid-1920s Shipley, a successful jeweler, met with one of his wealthy clientswho had just returned from the diamond cutting centers of Europe. This client informed him that his

By Barak Green, Al Gilbertson, Mary Johnson and James Shigley

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GIA and Its History with Cut

“Make” has played a role in diamond evaluationfor hundreds of years. As early as the 1500s, diamondmerchants were adjusting a diamond’s price basedon poor cut proportions (along with other considera-tions such as color and clarity). Nor was GIA the firstto suggest a method of grading diamonds based ontheir specific cut proportions or “make.” In 1942, itpublished an article by an early proponent of such amethod in its journal, Gems & Gemology. M. E.Vedder had created a system of diamond grading formodern round brilliants that required 22 proportionmeasurements to be averaged into seven cut factors(total depth, table size, crown height, pavilion depth,crown angle, girdle thickness, and culet size). Someof Vedder’s methods resemble aspects that GIAwould later adopt into its own diamond-cut gradingsystem in 1953.

A change in leadership sparked the birth ofGIA’s new grading system. In 1952, Robert Shipleyretired and was succeeded by Richard T. Liddicoat.Liddicoat had started at GIA in June 1940, and wasnamed director of education in 1946. Within a year oftaking over as president of GIA, Liddicoat (with thehelp of other experts on the GIA staff) developed andrefined a complete grading system for diamonds thatincluded a system for evaluating cut. This systemdebuted in April of 1953, as the first one-week“Diamond Grading and Evaluation” class in NewYork City.

In addition to establishing criteria for color andclarity1, this new grading system included an evalua-tion of cut. This was based on the weight differencebetween a diamond and what that diamond wouldhave weighed had it been originally cut toTolkowsky’s recommendations (e.g., a 53% table).Liddicoat’s new diamond grading system also basedits value system on market research. The accuracywith which the pricing guidelines given with thecourse’s new evaluation system matched the marketprices at the time was one reason it became so usefulin the diamond trade. (It is important to note thatthis accuracy was possible because of the long-termstability in diamond prices.)

The method of computing weight loss was basedon considering a half-octahedron of diamond roughand the largest faceted diamond that could be

attained from that rough within the proportionconstraints of the “American cut” standard. Volume(carat weight) was measured by modeling the diamondas two cones connected at their widest points, withthe point of the upper cone being truncated to formthe table facet (figure 1).

Taking the volume of the “American cut” diamondas a reference point (primarily because this cut almostalways represented the greatest loss of weight from apiece of rough), GIA computed the amount of “extra”weight any diamond with different proportionswould have. Charts of these differences were thenincorporated into a grading system that was basedon deductions for excess weight. The diamond wasevaluated on its “corrected weight,” which was thenused with color and clarity to compute its value. Thus,weight loss was equated with a price reduction thataffected the overall monetary value of the diamond.

This new system was meant to educate jewelers,and students training to be jewelers, in how to eval-uate, appraise, and purchase polished diamonds.Students were given mimeographed worksheets (fig-ure 2) to record their evaluations, and then were ableto check their results against those previously foundby instructors. Soon, students who had taken thecourse began sending in the diamonds they werepurchasing with their completed worksheets to dou-ble-check if they were still grading them correctly.Eventually, students realized that it was easier just tosend the diamonds they were selling to GIA andhave GIA return a completed worksheet. Since GIAassumed that former students knew how to computemonetary deductions based on color, clarity and

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Figure 1. In the early GIA grading system, two cones represented the volume of a diamond

GIA and Its History with Cut

finish grades, along with two proportion measure-ments (total depth percentage and table percentage),it included these factors on the sheets.

These returned worksheets evolved into theofficial GIA Diamond Grading Reports issued by theGIA Gem Laboratory. Although students of GIA’scourses were taught how to compute monetary eval-uations of diamonds from these reports, the reportsthemselves never showed any grade or valueassigned for a diamond’s cut propor-tions. An increasing number ofdealers in the United States andEurope began to use GIA DiamondGrading Reports to assure customersof the quality of the diamonds theywere buying (sometimes unseen). Inthis way, GIA Diamond GradingReports soon became a standard inthe diamond industry.

These reports were only part ofGIA’s interest in developing tools toaid in the evaluation of cut. In 1954,GIA developed the first version ofits ProportionScope™, an instrumentthat allowed a quick analysis of the proportions of around brilliant cut (RBC) diamond2. This versionwas a small box with a screen (on which were printedgraduated proportion lines) that attached to a micro-scope. A silhouette of the diamond’s profile was caston the screen, by which a grader could take quick

proportion measurements. In 1967, a new versionof the ProportionScope™ was released. This newversion was a separate instrument that also used acast silhouette of a diamond’s profile to evaluatecut (figure 3).

In 1957, Liddicoat strengthened GIA’s commit-ment to properly understanding and evaluatingdiamond cut when he sketched out a new classificationsystem in the Summer issue of Gems & Gemology.Liddicoat suggested that polished RBC diamondscould be classified into four categories based ontheir proportions. The proportions considered inthis new system were total depth-to-diameterratio, table size, and pavilion angle. These earlyguidelines were later adapted and expanded into aclassification system that could be used as a teachingaid. The new system incorporated table size, crownangle, pavilion depth, and girdle thickness into itsclassifications (figure 4). It is important to note thatthese classifications were merely suggestions thatreaders of the course materials might use as modelson which to base their own classification systems.Also, although these classifications were used toevaluate diamonds in coursework, they were neverused by GIA in the laboratory for grading reports.

Then, in the early 70s, GIA founditself embroiled in a controversyover diamond cut. Huisman Bros.,Inc. claimed that their new 144-facetdiamond was 32% more brilliant thanthe 58-facet diamond that was, andstill is, the norm for round brilliants.GIA stated that the difference betweenthe two cuts of diamonds had more todo with scintillation than brilliance. Toresolve the issue, the parties agreed topublish two articles (each articulatingone perspective) in the Spring, 1974issue of Gems & Gemology.

This agreement necessitated anew wave of research by GIA into the issue of dia-mond cut proportions and faceting. GIA showed thata 58-facet RBC diamond was more brilliant (i.e.,returned more light) than the 144-facet diamond byusing a photometer that measured the amount oflight returned from these diamonds.

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Figure 2. Sample of worksheet used to evaluate price of diamonds

Figure 3. Modern ProportionScope™

GIA and Its History with Cut

By 1979, GIA’s diamond courses had beenrevised to eliminate computations of monetary valuebased on a diamond’s proportions. GIA realized thatstandardized estimations of monetary value were notvalid in the (now quite volatile) global marketplace.One example of the divergence of trade realities fromteaching practice was table size: the “American cut”proportions that GIA often used in their evaluationsdid not always match the preference for larger tablesseen in some countries.

Consequently, GIA took the position that scientificevidence was needed in order to conclude that anyset of diamond proportions was superior for the 58-facet round brilliant cut. The research departmentbegan amassing that scientific evidence in 1989.Rather than limiting themselves to the traditionalapproach of looking at actual diamonds to evaluatecut, GIA researchers chose to address the problemusing computer graphics and data analysis tech-nologies. Its first job was to create a computer programthat accurately modeled the movement of light in atransparent solid with a round brilliant shape andthe optical properties of diamond. This approachhad two goals: the creation of realistic visual imagesof RBC diamonds, and the ability to calculate and eval-uate the optical performance of various combinationsof proportions for RBC diamonds. In June 1991, GIAprovided a brief introduction to their work.

Once the computer model was judged to be anaccurate representation of an internally flawless,colorless, perfectly symmetrical, RBC diamond, GIAbegan research on the effect that different propor-tions have on the aspects of a diamond’s appearance.The first attribute to be studied was brilliance —which was defined as the return of white light fromthe crown of a polished diamond, but excluded anylight that was merely reflected back from the surfaceof the crown facets; the latter was defined as glare.GIA published the results of this study in 1998.

GIA has continued its work on evaluating thecut properties and proportions of RBC diamonds.Current research is focusing on a second aspect of apolished diamond’s appearance: fire. In addition,GIA is comparing computer model results with actualdiamonds to ensure the accuracy of their computermodeling. This is simply the next chapter in GIA’s

long history of research into diamond cut proportions.We hope that you enjoyed this article, and invite

any feedback or comments that you may have. Youmay contact us by e-mail at DiamondCut@gia.edu

Originally Published: June 22, 2001GIA on Diamond Cut

BibliographyHemphill T. S., Reinitz I. R., Johnson M. L., and

Shigley J. E. (1998) Modeling the Appearance of the RoundBrilliant Cut Diamond: An Analysis of Brilliance. Gems &Gemology, Vol. 34, No. 3, pp. 158-183; available throughsubscription services at 760-603-4595 ext. 7142.

Manson D. (1992) Proportion Considerations in RoundBrilliant Diamonds. Proceedings of the InternationalGemological Symposium 1991 – Facing the Future, GemologicalInstitute of America, Santa Monica, CA, p. 60.

Tolkowsky M. (1919) Diamond Design: A Study of theReflection and Refraction of Light in a Diamond. Spon &Chamberlain, New York, 104 pp.

[This page was revised on August 17, 2001. Thanks toBert Krashes and Jim Coote for their comments.]

1It was at this time that GIA developed its color scale (which wouldbecome the standard in the industry). This new color scale was inno-vative in that it used “D” as the top color grade. GIA also refined theclarity scale that was currently being used at that time. By splitting theVVS, VS, SI, and I grades into two categories each, GIA made the scalemore precise. This clarity scale would also become the standard in thediamond industry.

2GIA’s ProportionScope™ provided a reliable instrument that was alsoeasy to use, at a time when several individuals were experimenting withsimilar concepts.

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MAKE CLASSES

Class

Table

Crown

Girdle

Pavilion

Culet

Finish

1 2 3* 4**

53-60%*** 61-64% 65-70% +70%

34-35° 32-34° 30-32° -30°

medium - slightly thick

43% 42-44% 41-46% -41/+46%

thin/ thick very thin / very thick

extremely thin/ extremely thick

none-medium slightly large large very large

very good - excellent

good fair poor

*Class 3 also includes stones with 51 or 52% tables or 37° crown angles.

**Class 4 also includes stones with tables less than 51%, crown angles more than 37°, or major symmetry variations.

***Table size for class 1 goes up to 61 or 62% in stones under 0.50 ct.

Figure 4. Classification system from the 1994 GIA Diamond Grading course