DOCSLIB.ORG

A Foundation for Grading the Overall Cut Quality of Round Brilliant

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Foundation for Grading the Overall Cut Quality of Round Brilliant AFOUNDATION FOR GRADING THE OVERALL CUT QUALITY OF ROUND BRILLIANT CUT DIAMONDS Thomas M. Moses, Mary L. Johnson, Barak Green, Troy Blodgett, Kim Cino, Ron H. Geurts, Al M. Gilbertson, T. Scott Hemphill, John M. King, Lisa Kornylak, Ilene M. Reinitz, and James E. Shigley GIA began its 15-year study of diamond cut by using a computer to model the way light behaves within a round brilliant cut diamond. From this model, GIA researchers developed proportion- based metrics to predict how diamonds would perform with regard to brilliance and fire. Continued research revealed several important variables that could not be evaluated effectively by computer modeling alone. Thus, the authors asked diamond manufacturers, dealers, retailers, and potential consumers to evaluate brightness (a term selected as more appropriate than brilliance), fire, and overall cut appearance of diamonds representing many different proportion combinations. These observations and discussions confirmed that additional factors, besides brightness and fire, contribute to diamond cut appearance, and that factors in addition to face-up appearance are important in assessing the quality of a diamond’s cut. With the trade interactions as a foundation, the authors (1) tested the brightness and fire metrics to find the best fit with human observations, (2) identified and quantified factors in addition to brightness and fire that contribute to face-up appearance, (3) developed a standard viewing environment that mimics common trade environments, (4) created the foundation for a comprehensive diamond cut grad- ing system, and (5) began development of reference software to predict the overall cut grade of a particular diamond. The GIA diamond cut grading system described here includes the compo- nents of brightness, fire, scintillation, polish, and symmetry, as well as weight and durability con- cerns, into a single overall grade for cut quality for standard round brilliants. f the Four Cs (color, clarity, cut, and carat • The use of proprietary devices, such as the weight), cut is the least understood—and GemEx BrillianceScope and ISEE2, which mea- least agreed upon—aspect of diamond sure one or more of the following aspects of dia- Oappearance. Current claims about the superiority of mond appearance: brilliance, fire, scintillation, certain round brilliant diamond cuts focus mostly and/or symmetry on three approaches: For GIA’s research on the evaluation of diamond • The use of specific sets of proportions (e.g., those cut, we started with a different approach, based on for the AGS 0, the AGA 1A, “Class 1” cuts [as the following questions: What makes a round bril- previously taught by GIA Education], the HRD liant cut (RBC, figure 1) diamond look the way it “Very Good” grades, “Ideal” cuts, and does? To what degree do differences among cutting “Tolkowsky” cuts) • The use of viewing devices to see specific pat- terns or pattern elements in diamonds (e.g., See end of article for About the Authors and Acknowledgments. FireScope, Symmetriscope, IdealScope, and vari- GEMS &GEMOLOGY, Vol. 40, No. 3, pp. 202–228. ous “Hearts-and-Arrows”–style viewers) © 2004 Gemological Institute of America 202 GRADING OVERALL CUT QUALITY GEMS &GEMOLOGY FALL 2004 Figure 1. The round bril- liant is the most popular diamond cut. Because of its popularity, assessment of this cut has been the sub- ject of considerable research. This image shows a wide range of uses for this style in commercial jewel- ry, as well as loose polished diamonds and diamond crystals. The loose polished diamonds weigh 1.05–3.01 ct, and the rough crystals weigh 2.14–2.49 ct. Jewelry and loose polished dia- monds courtesy of Ben Bridge Jewelers. Composite photo by Harold & Erica Van Pelt. proportions create observable distinctions? Which developed new metrics based on our results. We proportion sets produce results that are deemed also explain how we validated these new metrics attractive by most experienced observers? The first with further observation tests, and developed and stages of our research—which utilized advanced tested additional methods, including environments computer modeling—were described briefly by and procedures, for evaluating other essential Manson (1991), and then in detail by Hemphill et al. aspects of diamond appearance and cut quality. (1998) and Reinitz et al. (2001). Finally, on the basis of the information gathered Many other groups have used some form of com- during this extensive testing, we constructed a com- puter modeling to predict appearance aspects of dia- prehensive system for assessing the cut appearance mond proportion sets, including: Fey (1975), Dodson and quality of round brilliant cut diamonds. The (1978, 1979), Hardy et al. (1981), Harding (1986), van present article discusses the framework of this sys- Zanten (1987), Long and Steele (1988, 1999), tem, further details of which will be made available Tognoni (1990), Strickland (1993), Shigetomi (1997), in later publications. Shannon and Wilson (1999), Inoue (1999), and Sivovolenko et al. (1999). To our knowledge, how- ever, few if any of these other studies validated their BACKGROUND AND TERMINOLOGY modeling results by using observation tests of actu- The face-up appearance of a polished diamond is al diamonds, a major component of the research often described in terms of its brilliance (or brillian- described in the present article. The validation of cy), fire, and scintillation (see, e.g., GIA Diamond computer modeling by observations is essential in Dictionary, 1993). Historically, however, diamond the evaluation of diamond cut appearance, as with- appearance has been described using other terms as out this validation there is a risk of producing well; even the addition of scintillation to this list results that are not applicable to the real-world has been a relatively recent development (see, e.g., assessment of diamonds. Shipley, 1948). In this article, we discuss the key aspects of a Today, while brilliance, fire, and scintillation are well-cut diamond. We describe how we tested our widely used to describe diamond appearance, the previously published metrics (numerical values definitions of these terms found in the gemological based on mathematical models) for brilliance and literature vary, and there is no single generally fire by conducting observations with actual dia- accepted method for evaluating and/or comparing monds in typical trade environments and then these properties in diamonds. Further, experienced GRADING OVERALL CUT QUALITY GEMS &GEMOLOGY FALL 2004 203 members of the diamond trade use additional terms replaces brilliance, for the purposes of this article and when they assess the appearance of diamonds. In the forthcoming GIA diamond cut grading system. the course of this study, we interviewed dozens of Our interviews also confirmed that, in addition diamond manufacturers and dealers, in various to brightness, fire, and scintillation, the design and international diamond cutting centers and at trade craftsmanship of the diamond, as evidenced by its shows. (We also interviewed retailers and jewelry physical shape (e.g., weight and durability concerns) consumers, as described below.) We found that, in and its finish (polish and symmetry), are important addition to brilliance, fire, and scintillation, they indicators of a diamond’s overall cut quality. tended to use words such as life, pop, lively, dull, bright, or dead to describe a diamond’s cut appear- ance, although they could not always explain pre- MATERIALS AND METHODS cisely what they meant by such terms. In some This (third) stage of research evolved from that pre- cases, they would know whether or not they liked a sented in our previous two articles on diamond diamond, but were unable to articulate exactly why. appearance (Hemphill et al., 1998; Reinitz et al., To avoid potential confusion in describing cut 2001). Initially, we focused this stage on exploratory appearance, we have refined and expanded the defi- testing, to compare our computer-modeled predic- nitions of three essential terms, so that they more tions of brightness and fire with observations by clearly and accurately reflect what experienced experienced trade observers of selected actual dia- observers see in actual diamonds in everyday envi- monds. We found that the observers generally ronments. Throughout this article, we will use the agreed with each other but, in many cases, not with following definitions (see the glossary on p. 223 for a our predictions. We used these findings to create list of key diamond cut terms used in this article): and test additional brightness and fire metrics, using a broader group of observers and diamonds. • Brightness—the appearance, or extent, of internal Extensive observation testing with diamonds and external reflections of “white” light seen in a was needed to: (1) determine how well the original polished diamond when viewed face-up. Note and subsequent metric predictions compared to that although we originally used brilliance to actual observations; (2) establish thresholds at describe this property (Hemphill et al., 1998; which differences defined by the model are no Reinitz et al., 2001), as we proceeded further with longer discerned by an experienced observer; (3) see our study, we found that many individuals in the the broad range of effects that might be statistically trade and general public include other appear- significant with a large and varied sample of dia- ance aspects (such as contrast) in their use of that monds; (4) determine
Load more

Recommended publications
  • Finish, Culet Size, and Girdle Thickness: Categories of the GIA Diamond Cut Grading System
    Finish, Culet Size, and Girdle Thickness: Categories of the GIA Diamond Cut Grading System This booklet summarizes the relationship of Finish, Culet Size, and Girdle Thickness to the GIA Cut Grading System for round brilliant diamonds. It is intended to help members of the jewelry trade better understand the attributes of diamond appearance, and how those attributes are evaluated within the GIA Cut Grading System. Finish—Polish and Symmetry In the GIA Cut Grading System for standard round brilliant To determine the relationship between finish and overall diamonds, finish (for Polish and Symmetry features) is cut quality, GIA conducted extensive observation testing factored into the final overall cut grade as follows: of numerous diamonds using standardized lighting and viewing conditions. Observations of diamonds with • To qualify for an Excellent cut grade, polish and comparable proportions, but differing in their polish and symmetry must be Very Good or Excellent. symmetry categories, were analyzed to determine the effects of finish on overall cut appearance. In this way, • To qualify for a Very Good cut grade, both polish GIA found that a one grade difference between the other and symmetry must be at least Good. aspects of a diamond’s cut grade and its polish and • To qualify for a Good cut grade, both polish and symmetry assessments did not significantly lower a symmetry must be at least Fair. trained observer’s assessment of face-up appearance, and could not be discerned reliably with the unaided eye— • To qualify for a Fair cut grade, both polish and e.g., polish and/or symmetry descriptions of Very Good symmetry must be at least Fair.
    [Show full text]
  • IDENTIFYING and VALUING OLD EUROPEAN CUT DIAMONDS Richard B
    FEATURE ARTICLE IDENTIFYING AND VALUING OLD EUROPEAN CUT DIAMONDS Richard B. Drucker, GIA GG, Honorary FGA Identifying an old European cut diamond may seem simple but there is a set of GIA standards that determine from their perspective whether it is or is not. This set of standards is not widely accepted by vintage jewelry dealers that struggle with some of the non-calls. For the past several years, prices have risen significantly, sometimes even above the price of a modern brilliant when hard to find and in demand. While that is true in some sizes and qualities, the market is softening in other. uring the past decade, the gemguide has featured will be no cut grade assigned. A polish and symmetry grade several articles on old european cut diamonds. The will still appear. Dfirst article of the same title as this feature here, ap - peared in the November 2010 issue (Volume 29, issue 6). in in our article in 2010, we published the criteria used by the September 2011 (Volume 30, issue 5) another feature article giA to determine if a diamond was to be called old euro - appeared discussing the ongoing dilemma over old european pean cut. They look at four parameters only and today, they cut diamonds, specifically nomenclature on grading reports still consider only those four. Figure 1. The parameters are and the history of cutting styles and cut grading. Today, we as follows. continue to debate nomenclature. Table size: less than or equal to 53% Crown angle: greater than or equal to 40 degrees in November 2012 (Volume 31, issue 6), we published a mar - Lower half facet length: less than or equal to 60% ket trends article showing how the price of these diamonds Culet size: slightly large or larger has continued to rise over the years in comparison to round brilliant cuts.
    [Show full text]
  • Evaluation of Brilliance, Fire, and Scintillation in Round Brilliant
    Optical Engineering 46͑9͒, 093604 ͑September 2007͒ Evaluation of brilliance, fire, and scintillation in round brilliant gemstones Jose Sasian, FELLOW SPIE Abstract. We discuss several illumination effects in gemstones and University of Arizona present maps to evaluate them. The matrices and tilt views of these College of Optical Sciences maps permit one to find the stones that perform best in terms of illumi- 1630 East University Boulevard nation properties. By using the concepts of the main cutter’s line, and the Tucson, Arizona 85721 anti-cutter’s line, the problem of finding the best stones is reduced by E-mail: [email protected] one dimension in the cutter’s space. For the first time it is clearly shown why the Tolkowsky cut, and other cuts adjacent to it along the main cutter’s line, is one of the best round brilliant cuts. The maps we intro- Jason Quick duce are a valuable educational tool, provide a basis for gemstone grad- Jacob Sheffield ing, and are useful in the jewelry industry to assess gemstone American Gem Society Laboratories performance. © 2007 Society of Photo-Optical Instrumentation Engineers. 8917 West Sahara Avenue ͓DOI: 10.1117/1.2769018͔ Las Vegas, Nevada 89117 Subject terms: gemstone evaluation; gemstone grading; gemstone brilliance; gemstone fire; gemstone scintillation; gemstone cuts; round brilliant; gemstones; diamond cuts; diamonds. James Caudill American Gem Society Advanced Instruments Paper 060668R received Aug. 28, 2006; revised manuscript received Feb. 16, 8881 West Sahara Avenue 2007; accepted for publication Apr. 10, 2007; published online Oct. 1, 2007. Las Vegas, Nevada 89117 Peter Yantzer American Gem Society Laboratories 8917 West Sahara Avenue Las Vegas, Nevada 89117 1 Introduction are refracted out of the stone.
    [Show full text]
  • Cut Shape and Style the Diamond Course
    Cut Shape and Style The Diamond Course Diamond Council of America © 2015 Cut Shape and Style In This Lesson: • The C of Personality • Optical Performance • The Features of Cut • The Round Brilliant • Classic Fancy Shapes • Branded Diamond Cuts • Shape, Style, and Cost • Presenting Cuts and Brands THE C OF PERSONALITY In the diamond industry the term “cut” has two distinct meanings. One is descriptive. It refers to the diamond’s shape and faceting style. The other relates to quality, and includes proportions, symmetry, and polish. Most customers are familiar with only the first meaning – cut shape and style. That’s the aspect of All sorts of cutting shapes are cut you’re going to examine in this lesson. The next possible with diamonds. lesson explores the second part of this C. For many customers, cut shape and style is part of their mental image of a diamond. Shape contrib- utes to the messages that a diamond sends about the personality of the one who gives or wears it. When presenting this aspect of cut, you need to match the images and messages of the diamonds you show with the customers you serve. With branded diamond cuts, you may need to explain other elements that add appeal or value. When you’ve accomplished these objectives you’ve taken an important step toward closing the sale. The Diamond Course 5 Diamond Council of America © 1 Cut Shape and Style Lesson Objectives When you have successfully completed this lesson you will be able to: • Define the optical ingredients of diamond’s beauty. • Describe diamond cuts in understandable terms.
    [Show full text]
  • The Ideal Brilliant Cut: Its Beginnings to Today
    MICHAEL D. COWING is the author of Objective Diamond Clarity Grading, an educator, gemologist and appraiser operating an Accredited Gemologist Association Certified Gem Laboratory. His career in diamonds, gems, and gemology spans 35 years. The Ideal Brilliant Cut: Its Beginnings to Today Figure 1. Face-up view of the Ideal Figure 2. 20° Tilt from face-up Figure 3. 20° Tilt forward from the side Cut at its beginning in the 1860’s view of the early Ideal Cut. view of the early Ideal Cut. time frame. Figure 4. Face-up view of today’s Figure 5. 20° tilt from face-up Figure 6. 20° tilt forward from the side view Ideal Cut with fundamentally the view of today’s Ideal Cut. of today’s Ideal Cut. same main angles as the early Ideal. Introduction back angle1.“ It was also known in Europe around the turn of the 19th century as the American Cut. The Ideal Cut’s Since its beginnings in the early 20th century to the present appearance is transformed in Figures 4-6 with today’s day, confusion and misunderstanding has frequently proportions, (larger table size, longer lower girdle facets, surrounded the use (or misuse) of the term “Ideal Round thicker girdle, etc.), while retaining the same fundamental Brilliant Cut,” its defining properties and origin. Some have crown and pavilion main angles which are key to its beauty. advocated eliminating its use altogether. Through the examination of the Ideal Round Brilliant Cut’s (Ideal Cut The Ideal’s beginning with the American Cut hereafter) evolution, this article endeavors to clear up its history, clarify its defining properties and in the process The beginning of today’s Ideal Round Brilliant Cut was the dispel the misunderstanding and mythology surrounding this design attributed to Henry Morse and his diamond cutting most popular of diamond cuts.
    [Show full text]
  • Fall 1998 Gems & Gemology
    FALL 1998 VOLUME 34 NO. 3 TABLE OF CONTENTS EDITORIAL 157 Demystifying Diamond Cut William E. Boyajian FEATURE ARTICLES 158 Modeling the Appearance of the Round Brilliant Cut Diamond: An Analysis of Brilliance pg. 159 T. Scott Hemphill, Ilene M. Reinitz, Mary L. Johnson, and James E. Shigley 184 Cultured Abalone Blister Pearls from New Zealand Cheryl Y. Wentzell NOTES AND NEW TECHNIQUES 202 Estimating Weights of Mounted Colored Gemstones Charles I. Carmona REGULAR FEATURES 212 Gem Trade Lab Notes 218 Gem News pg. 198 231 1998 Challenge Winners 232 Book Reviews 234 Gemological Abstracts ABOUT THE COVER: Because abalone pearls are admired for their rarity, attractive col- ors, and striking iridescence, efforts have been made to culture them for more than a cen- pg.210 tury. Only recently has commercial production of cultured abalone blister pearls been achieved. A feature article in this issue examines the history, production, marketing, and pg. 217 identifying characteristics of assembled cultured blister pearls from one major producer, Empress Abalone Ltd., using New Zealand’s Haliotis iris. These abalone “mabés” are being incorporated into distinctive jewelry designs, together with colored stones and dia- monds. The gold pendants and rings shown here contain abalone “mabés” ranging from 12.5 to 17.3 mm in diameter. Jewelry courtesy of designer Ian Henderson, Dunedin, New Zealand. Photo © Harold & Erica Van Pelt––Photographers, Los Angeles, California. Color separations for Gems & Gemology are by Pacific Color, Carlsbad, California. Printing is by Fry Communications, Inc., Mechanicsburg, Pennsylvania. © 1998 Gemological Institute of America All rights reserved. ISSN 0016-626X Demystifying diamond cut he proper assessment of cut in dia- important appearance concept, bril- We also know that there are many monds has long been an elusive, but liance, based on what the authors call combinations of proportions that yield T intriguing, goal.
    [Show full text]
  • MODELING the APPEARANCE of the ROUND BRILLIANT CUT DIAMOND: an ANALYSIS of BRILLIANCE by T
    MODELING THE APPEARANCE OF THE ROUND BRILLIANT CUT DIAMOND: AN ANALYSIS OF BRILLIANCE By T. Scott Hemphill, Ilene M. Reinitz, Mary L. Johnson, and James E. Shigley Of the “four C’s,”cut has historically been the he quality and value of faceted gem diamonds are most complex to understand and assess. This often described in terms of the “four C’s”: carat article presents a three-dimensional mathemat- weight, color, clarity, and cut. Weight is the most ical model to study the interaction of light with Tobjective, because it is measured directly on a balance. a fully faceted, colorless, symmetrical round- Color and clarity are factors for which grading standards brilliant-cut diamond. With this model, one have been established by GIA, among others. Cut, however, can analyze how various appearance factors (brilliance, fire, and scintillation) depend on is much less tractable. Clamor for the standardization of proportions. The model generates images and a cut, and calls for a simple cut grading system, have been numerical measurement of the optical efficien- heard sporadically over the last 25 years, gaining strength cy of the round brilliant—called weighted light recently (Shor, 1993, 1997; Nestlebaum, 1996, 1997). Unlike return (WLR)—which approximates overall color and clarity, for which diamond trading, consistent brilliance. This article examines how WLR val- teaching, and laboratory practice have created a general con- ues change with variations in cut proportions, sensus, there are a number of different systems for grading in particular crown angle, pavilion angle, and cut in round brilliants. As discussed in greater detail later in table size.
    [Show full text]
  • Star Brilliant Cut 57 Facet Diamond, Correspondence ID: I-YX6QVV; SR# 1-1069429181
    United States Copyright Office Library of Congress · 101 Independence Avenue SE · Washington, DC 20559-6000 . www.copyright.gov March 20, 2017 Howard Rockman Law Offices of Howard B. Rockman, P.C. 525 W Monroe Street, Suite 2360 Chicago, IL 60661 Re: Second Request for Reconsideration for Refusal to Register Star Brilliant Cut 57 Facet Diamond, Correspondence ID: I-YX6QVV; SR# 1-1069429181 Dear Mr. Rockman: The Review Board of the United States Copyright Office (the "Board") has examined Sadamatsu Company Limited' s ("Sadamatsu") second request for reconsideration of the Registration Program's refusal to register a copyright claim in the work titled "Star Brilliant Cut 57 Facet Diamond" (the "Work"). After reviewing the application, the deposit copy, and the relevant correspondence, along with the arguments in the second request for reconsideration, the Board affirms the Registration Program' s denial of registration of this copyright claim. I. DESCRIPTION OF THE WORK The Work is a design of a cut diamond with fifty-seven facets, or flat faces of the stone. The diamond is comprised of the flat top surface area (the "table"), twenty-five facets on the top portion of the diamond (the "crown"), thirty facets on the cone-shaped lower part of the stone (the "pavilion"), as well as the bottom tip of the stone (the "culet"). The Work's facets are a collection of triangles, quadrilaterals, and a decagon. Looking down at the Work from the table and crown shows a large five-point star with a smaller five-point star in the larger star' s center. Photographic reproductions of the Work are included as Appendix A.
    [Show full text]
  • GIA's Symmetry Grading Boundaries for Round Brilliant Cut Diamonds
    GIA’S SYMMETRY GRADING BOUNDARIES FOR ROUND BRILLIANT CUT DIAMONDS Ron H. Geurts, Ilene M. Reinitz, Troy Blodgett, and Al M. Gilbertson ations during planning and cutting. Likewise, mak- ers of non-contact optical scanners have been inter- Grade boundary limits are presented for 10 ested in guidelines for how measurable symmetry symmetry parameters of the round brilliant cut parameters affect the GIA symmetry grade. The diamond. Starting in early 2012, these values grade boundaries presented here offer a substantive will be used to support and constrain visual estimate of the symmetry grade for any round bril- symmetry grading on GIA diamond reports. liant cut diamond. For manufacturers, the boundaries provide In GIA’s laboratory, polished diamonds are mea- useful predictions of symmetry grades. Other sured with a non-contact optical scanner early in the symmetry features of faceted diamonds will grading process. Later, polish and symmetry are eval- continue to be evaluated visually. uated visually at 10× magnification, using a standard procedure. As described in Gillen et al. (2005), specif- ic parameter- and facet-related features are consid- ered in grading symmetry. This article presents numerical grade limits for 10 important symmetry ince 2006, GIA has used certain proportion mea- parameters that can be measured accurately enough surements obtained with non-contact optical to support visual symmetry grading. Although mea- Sscanners to grade the cut of round brilliant dia- sured values have been available to graders as a guide monds. Improvements in the operation and accuracy for several years, beginning in 2012 GIA will use of these instruments now enable us to also measure measured values and apply these boundary limits some symmetry parameters during the grading pro- strictly when grading symmetry for round brilliant cess.
    [Show full text]
  • The Essential Engagement Ring Handbook – Lisa Krikawa
    The Essential Engagement Ring Handbook by Lisa Krikawa 1 THE ESSENTIAL ENGAGEMENT RING HANDBOOK Make Knowledgeable Choices and Avoid Expensive Mistakes When Investing in the Most Significant Jewelry Purchase of Your Life By Lisa Krikawa www.krikawa.com The Essential Engagement Ring Handbook by Lisa Krikawa 2 Copyright © 2016 by Lisa R. Krikawa All rights reserved. This book or parts thereof may not be reproduced in any form, stored in any retrieval system, or transmitted in any form by any means—electronic, mechanical, photocopy, recording, or otherwise—without prior written permission of the publisher, except as provided by United States of America copyright law. For permission requests, write to the publisher, at “Attention: Permissions Coordinator,” at the address below. Created in the United States of America Visit the author’s website at www.krikawa.com. First Edition This book and the content provided herein are simply for educational purposes. Every effort has been made to ensure that the content provided in this book is accurate and helpful for our readers at publishing time. However, this is not an exhaustive treatment of the subjects. No liability is assumed for losses or damages due to the information provided. You are responsible for your own choices, actions, and results. Lisa Krikawa Krikawa Jewelry Designs 21 E. Congress St. Tucson, AZ 85701 www.krikawa.com The Essential Engagement Ring Handbook by Lisa Krikawa 3 This book is dedicated to PSI Seminars, PLD Team #57 To the Owner, Trainer, Coaches and Players, “Fly Like Eagles!” www.krikawa.com The Essential Engagement Ring Handbook by Lisa Krikawa 4 Table of Contents Preface ................................................................................................................................
    [Show full text]
  • The Optical Design of Gemstones
    The Optical Design T of Gemstones José M. Sasián, Peter Yantzer and Tom Tivol Peter Yantzer The best jewellers have always been 100% aware that the quality of the cut is 53% primarily responsible for making Table Bezel a stone appear brilliant and Crown 16.2% colorful, or dull and lifeless. 34.5° Today, advanced optical design software is being Girdle used to optimize gem- cutting by modeling light propagation 40.7° through stones. Pavilion Figure 1. Tolkowsky proportions and diamond nomenclature. here is new excitement in the gem- metrics based on light response and stone industry. Today, for the first beauty have been introduced. The gem- T time, scientific advances are allow- buying public also benefits from an ing the detailed optical design, precision understanding of light propagation in cutting and characterization metrology gemstones. The main focus of this article of beautiful jewels. Understanding how to is to describe the role of optics in gem- cut a stone to best disperse and break stone design along with related trends in light into a plurality of colorful scintilla- the gemstone industry. tions has consistently been a major focus of the gemstone industry. Diamonds, for The complexities of cut example, are marketed on the basis of the By trial and error, ancient jewelers pro- Four C’s: cut, color, clarity and carat duced cuts that refracted light to give illu- weight. Of these four attributes, "cut" is mination life to gemstones. One of the the least understood by the general public first thought-provoking studies on how and by jewelry industry professionals.
    [Show full text]
  • CUT the Cut Or “Shape and Make” of a Diamond Can Be Considered
    The Third “C” – CUT The cut or “shape and make” of a diamond can be considered the most important of the “C”’s because the quality of the cut is what gives the diamond its brilliance and beauty and strongly contributes to the diamond’s value. The cut of the diamond is fashioned by human hands and is the only “C” that is not determined in nature. Diamond cutters cut and polish diamond rough by hand into objects of beauty. It requires a master cutter to fashion an ideally cut diamond. Facets are the tiny planes on the diamond’s surface, which give it sparkle and fire. The manner in which the facets are angled to each other and the diamond's proportions determine the brilliance (reflection of light from inside the diamond), dispersion (color refraction-the twinkling of colors) and scintillation (reflection of light from the surfaces of its facets), or more simply, its light refraction, display of spectral colors and their movement, respectively. In order to maximize this brilliance, the diamond cutter must place each of the diamond's facets, which act as light-dispersing mirrors, in exact geometric relation to one another. On a classic Round Brilliant cut diamond, fifty-eight facets must be precisely aligned. Few diamonds are cut to exacting standards since diamond cutters try to maximize their returns on the raw material by leaving the stone as large as possible with minimum waste. As a result, the proportions, symmetry and perfection of the cut and shape may be delegated to play a secondary role.
    [Show full text]