DOCSLIB.ORG

D19 Synth&Treat 04Update

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
D19 Synth&Treat 04Update Diamonds & DiamondGrading Synthetics and Treatments19 Table of Contents Subject Page Synthetic Diamonds . 2 Early Research . 3 Success and Progress . 3 Applications in Industry and Jewelry . 9 Chemical Vapor Deposition . 12 Detecting Synthetic Diamonds . 13 Detecting CVD Synthetic Diamonds . 20 Color Treatments . 21 Irradiation . 22 Annealing . 26 Heat and Pressure . 26 Coatings . 31 Recognizing Color Modifications . 31 Clarity Treatments . 34 Laser Drilling . 34 Internal Laser Drilling . 35 Fracture Filling . 35 Detecting Fracture Filling . 36 Disclosing Fracture Filling . 38 Treated Diamonds and the Marketplace . 39 Key Concepts . 41 Key Terms . 42 ©2002 The Gemological Institute of America All rights reserved: Protected under the Berne Convention. No part of this work may be copied, reproduced, transferred, or transmitted in any form or by any means whatsoever without the express written permission of GIA. ©Printed in the United States. Reprinted 2004 Revised and updated 2008 Cover photos: (clockwise from left) Tino Hammid/GIA, Christie’s Images Inc., John Koivula/GIA, Vincent Cracco/GIA. Back cover: Glodiam Israel Ltd. Facing page: The diamonds in this stunning brooch and earring suite are all natural, but they feature both treated and natural colors. ©1998 Tino Hammid SYNTHETICS AND TREATMENTS People have revered the diamond as a precious product of nature for Key Concepts thousands of years. By now, you’ve learned about its progress from Diamond’s beauty, rarity, and value simple carbon atoms to rough diamond to finished gem. You understand how diamond’s rarity gives it exceptional value in the gem world. Is it inspire research into synthesis and any wonder that, through the ages, alchemists and researchers have made treatment. countless attempts to duplicate and enhance diamond’s unique properties and structure? Through careful research, scientists have discovered ways to make natural diamond “better”—to hide its imperfections or to make it a more attractive color. Benvenuto Cellini, the sixteenth-century Italian goldsmith and gem historian, wrote about early gemstone color treatments. He described the heating of sapphire, topaz, amethyst, and other gem minerals in fire until they lost their color—and imitated diamond. Those early searches for diamond look-alikes later developed into searches for techniques to make diamonds. Researchers tried to find just ©2002 GIA. All rights reserved. 1 DIAMONDS AND DIAMOND GRADING 19 the right combination of ingredients, temperature, and pressure that would allow technology to do nature’s work. In the 1950s, scientists began making synthetic diamonds. Now they’re widely used in industry, mostly in cutting instruments and abrasives. A few have been produced for the gem market. In this assignment, you’ll learn about synthetic diamonds and about color and clarity treatments, along with some basic detection skills. Now that synthetics and treatments have become part of the diamond industry, gem professionals who can detect them will be in demand at every level. By the end of this assignment, you’ll have gained valuable knowledge to help you meet that demand. SYNTHETIC DIAMONDS I When was synthetic diamond first successfully grown? I How do synthetic diamonds fit into industry and the jewelry market? I What are some basic detection methods for synthetic diamonds? Michael Nicholson/Corbis Sixteenth-century Florentine sculptor As you learned in Assignment 18, there’s an important difference between and goldsmith Benvenuto Cellini wrote synthetic diamonds and simulants. Synthetic diamonds are made in the some of the earliest descriptions of laboratory, and they have essentially the same chemical composition and gemstone treatments. crystal structure as natural diamonds—or at least as close as researchers can make them. Their physical and optical properties are nearly the same as natural diamonds. Simulants, on the other hand, only look like diamonds. They can be natural or made in a lab from a variety of materials, and their chemical compositions and physical and optical properties are different from those of diamond. Synthetic diamond— Manufactured diamond with essentially the same physical, chemical, and optical properties as natural diamond. Joseph Schubach Although this manmade material—synthetic moissanite—imitates the look of diamond, it doesn’t share its properties. 2 SYNTHETICS AND TREATMENTS It wasn’t until the development of giant presses, like this one at GE, that scientists were able to create the high levels of heat and pressure needed to synthesize diamonds. EARLY RESEARCH In 1797, English chemist Smithson Tennant demonstrated that diamond was nothing more than a very dense form of pure carbon. The fact that carbon was plentiful inspired researchers to explore the possibility of turning some of it into much rarer diamond. Through the 1800s and early 1900s, many researchers and chemists tried to create synthetic diamond from a variety of carbon-containing com- pounds. Early technical realities stopped them from making much progress: They knew they needed high levels of heat and pressure for diamond formation, but didn’t have the technology to produce the right conditions. SUCCESS AND PROGRESS Then, in 1941, Dr. Percy W. Bridgman, an American researcher who specialized in high-pressure physics, came to an agreement with the General Electric Corporation (GE) and other commercial parties. GE assigned 3 DIAMONDS AND DIAMOND GRADING 19 Hulton-Deutsch Collection/Corbis Percy Williams Bridgman was one of the pioneers of diamond synthesis research. Bridgman to design a laboratory especially for the production of synthetic diamonds. Before World War II interrupted the project, Bridgman and his colleagues made important advances in high-pressure technology—but no diamonds. In 1951, GE formed another research group to expand on Bridgman’s work. By 1953, they had designed equipment capable of reaching and maintaining extreme pressures and temperatures. After that, the only modifications they made were to the apparatus that actually held and compressed the raw materials. Finally, a belt-type apparatus designed by team member Dr. Tracy Hall succeeded. GE scientists created their first batch of synthetic industrial diamonds in December 1954. After careful testing of the products and successful repetition of the process, they announced the achievement to the world on February 15, 1955. 4 SYNTHETICS AND TREATMENTS Key Concepts Research into diamond synthesis began before 1800, but producers didn’t succeed until the 1950s. Bettmann/Corbis Although Swedish researchers also succeeded in synthesizing diamonds, GE was the first to document the process. These tiny diamonds represent that first success. A Swedish electric company—Allmana Svenska Elektriska Aktiebolaget—had actually made diamonds two years earlier. Their scientists started some diamond-making projects in the 1940s, then abandoned them. They began again in the early 1950s. In February 1953, they made several tiny synthetic diamonds. Even better, they were able to repeat their success in May and November of the same year. But the Swedish scientists decided that their method was too difficult, too slow, and too costly to be commercially feasible. They didn’t announce their accomplishment until two years after GE’s success. By then, it was too late for them to be recognized as the first diamond makers. Today, almost all synthetic diamonds are grown using the process developed by the diamond synthesis pioneers. This process is called high- pressure, high-temperature, or HPHT. GE began marketing synthetic diamond grit in late 1957. They kept their process secret for the next two years under federally enforced secrecy regulations. GE filed worldwide patents in 1959, and the team published details of its procedures. De Beers soon followed with their High pressure, high temperature own patent for diamond synthesis. (HPHT)—Diamond synthesis You might think that the step from growing experimental batches of method that mimics the pressure tiny synthetic diamond crystals to creating large, high-quality crystals and temperature conditions that would be a relatively small one. But progress was limited. Larger crystals lead to natural diamond take a lot longer to form than tiny ones. The challenge for researchers formation. 5 DIAMONDS AND DIAMOND GRADING 19 carbon source heating anvil element metal flux high-pressure cell seed crystal There’s a container—or high-pressure cell—at the center of the diamond press. Within the cell, carbon atoms are sub- jected to intense heat and pressure. The atoms travel though the growth medium— a metal flux—and crystallize on the seed crystal as synthetic diamond. Both by Peter Johnston/GIA All diamond presses work on the same principle: extremely high pressures and temperatures applied to the necessary ingredients. This illustration shows the six anvils in a modern diamond press. They’re pushed inward by pistons—that aren’t shown here—and exert enormous pressures on a tiny central container where crystal growth takes place. was to increase crystal size and, at the same time, control the quality of the crystals. The size of the necessary equipment was also a limiting factor. The GE research team worked on solving these problems and, in 1970, announced the creation of the first cuttable, gem-quality synthetic diamonds. In 1970 and 1971, Lazare Kaplan and Sons of New York cut some of those first gem-quality synthetic diamonds, which weighed about 1 ct. each in rough form. Fashioned stones cut from those crystals ranged from 0.26 ct. to 0.46 ct. in weight, and from F to J in color. There were also some yellows and blues, and the highest clarity was VS. Over the next 14 years, a few synthetic gem-quality diamonds were used for research and for special scientific uses. During this period, re- searchers solved the technical problems preventing large-scale manufacture. 6 SYNTHETICS AND TREATMENTS Robert Weldon/GIA Most synthetic diamonds are small and yellow in color. These specimens—produced in Russia—range from 0.14 ct. to 0.88 ct. In 1985, Japan’s Sumitomo Electric Industries began commercial produc- tion of large, high-quality synthetic diamonds.
Load more

Recommended publications
  • A Defect Study and Classification of Brown Diamonds with Deformation
    minerals Article A Defect Study and Classification of Brown Diamonds with Deformation-Related Color Thomas Hainschwang 1,*, Franck Notari 2 and Gianna Pamies 1 1 GGTL Laboratories, Gnetsch 42, 9496 Balzers, Liechtenstein; [email protected] 2 GGTL Laboratories, 2 bis route des Jeunes, 1227 Geneva, Switzerland; [email protected] * Correspondence: [email protected]; Tel.: +423-262-24-64 Received: 3 September 2020; Accepted: 7 October 2020; Published: 12 October 2020 Abstract: For this study, the properties of a large sample of various types of brown diamonds with a deformation-related (referred to as “DR” in this work) color were studied to properly characterize and classify such diamonds, and to compare them to pink to purple to red diamonds. The acquisition of low temperature NIR spectra for a large range of brown diamonds and photoexcitation studies combined with various treatment experiments have opened new windows into certain defect characteristics of brown diamonds, such as the amber centers and naturally occurring H1b and H1c centers. It was determined that the amber centers (referred to as “AC” in this work) exhibit rather variable behaviors to annealing and photoexcitation; the annealing temperature of these defects were determined to 1 range from 1150 to >1850 ◦C and it was found that the 4063 cm− AC was the precursor defect of many other ACs. It is suggested that the amber centers in diamonds that contain at least some C centers are essentially identical to the ones seen in diamonds without C centers, but that they likely have a negative charge.
    [Show full text]
  • Type Classification of Diamonds
    THE “TYPE” CLASSIFICATION SYSTEM OF DIAMONDS AND ITS IMPORTANCE IN GEMOLOGY Christopher M. Breeding and James E. Shigley Diamond “type” is a concept that is frequently mentioned in the gemological literature, but its rel- evance to the practicing gemologist is rarely discussed. Diamonds are broadly divided into two types (I and II) based on the presence or absence of nitrogen impurities, and further subdivided according to the arrangement of nitrogen atoms (isolated or aggregated) and the occurrence of boron impurities. Diamond type is directly related to color and the lattice defects that are modi- fied by treatments to change color. Knowledge of type allows gemologists to better evaluate if a diamond might be treated or synthetic, and whether it should be sent to a laboratory for testing. Scientists determine type using expensive FTIR instruments, but many simple gemological tools (e.g., a microscope, spectroscope, UV lamp) can give strong indications of diamond type. emologists have dedicated much time and critical to evaluating the relationships between dia- attention to separating natural from syn- mond growth, color (e.g., figure 1), and response to G thetic diamonds, and natural-color from laboratory treatments. With the increasing availabili- treated-color diamonds. Initially, these determina- ty of treated and synthetic diamonds in the market- tions were based on systematic observations made place, gemologists will benefit from a more complete using standard gemological tools such as a micro- understanding of diamond type and of the value this scope, desk-model (or handheld) spectroscope, and information holds for diamond identification. ultraviolet (UV) lamps. While these tools remain Considerable scientific work has been done on valuable to the trained gemologist, recent advances this topic, although citing every reference is beyond in synthetic diamond growth, as well as irradiation the scope of this article (see, e.g., Robertson et al., and high-pressure, high-temperature (HPHT) treat- 1934, 1936; and Kaiser and Bond, 1959).
    [Show full text]
  • Brown Diamonds and HPHT Treatment
    9th International Kimberlite Conference Extended Abstract No. 9IKC-A-00405, 2008 Brown diamonds and HPHT treatment David Fisher Diamond Trading Company, DTC Research Centre,Belmont Road, Maidenhead, SL6 6JW, UK A significant proportion of gem quality natural illustrates, if viewed in the correct orientation, the diamonds have a brown component to their colour. brown colour can be seen to be concentrated in so- Whilst a number of different defect centres can give called slip-bands and a clear link with plastic rise to a brown hue, the main process associated with deformation is evident. the generation of brown colour is plastic deformation. Whilst plastic deformation is necessary to produce such Not all plastically deformed diamonds are brown, brown colouration, not all plastically deformed however, and, in spite of many years of speculation diamonds are brown. The DiamondView image (short about and investigation into this problem, the specific wave uv excited luminescence) of a colorless type IIa defects associated with the brown colour have until diamond (Figure 2) shows blue luminescing recently remained a mystery. dislocations in polygonised networks, indicative of The need to gain better understanding of this plastic deformation at some point in the diamond’s phenomenon has been given added impetus by the history followed by a period of annealing during which discovery that high pressure high tempertaure (HPHT) dislocations have undergone glide and climb to arrange treatment can be applied to remove the brown colour in into a lower energy network configuration. diamonds. In addition to the scientific understanding systematic studies of such treatment can provide, there is also a strong commercial incentive to carry out such treatment on relatively low value brown stones to improve their colour and increase their value.
    [Show full text]
  • GE POL DIAMONDS: BEFORE and AFTER by Christopher P
    GE POL DIAMONDS: BEFORE AND AFTER By Christopher P. Smith, George Bosshart, Johann Ponahlo, Vera M. F. Hammer, Helmut Klapper, and Karl Schmetzer This study of type IIa GE POL diamonds arch 1, 1999 is a watershed date in the gem before and after HPHT annealing by GE sig- and jewelry trade. This is when General nificantly expands on their characterization. Electric (GE) and Lazare Kaplan International The color change was dramatic: from the N–O (LKI)M unveiled their latest contribution to the diamond and range through Fancy Light brown before, to jewelry industry: diamonds that had undergone a new GE D–H after. However, there was little change to process “designed to improve their color, brilliance, and the inclusions, graining, and strain as a result brightness” (Rapnet, 1999). Colloquially, these diamonds of HPHT exposure. Photoluminescence (PL) studies—conducted at liquid helium, liquid became known as “GE POL” or “Pegasus” diamonds, nitrogen, and room temperatures in the because they were being marketed through LKI subsidiary 245–700 nm range—identified a significant Pegasus Overseas Ltd. (POL). At the July 2000 Jewelers of reconfiguration of the lattice involving substi- America trade show in New York, however, the brand name tutional impurities, vacancies, and intersti- Bellataire was officially launched. tials. Key regions of PL activity included the The first gemological description of GE POL diamonds areas of the N3, H3, and N-V centers. X-ray appeared in fall 1999, when GIA published an overview of the topography identified the extent of lattice dis- macroscopic and microscopic features observed in 858 GE tortion.
    [Show full text]
  • The “Type” Classification System of Diamonds and Its Importance in Gemology
    THE “TYPE” CLASSIFICATION SYSTEM OF DIAMONDS AND ITS IMPORTANCE IN GEMOLOGY Christopher M. Breeding and James E. Shigley Diamond “type” is a concept that is frequently mentioned in the gemological literature, but its rel- evance to the practicing gemologist is rarely discussed. Diamonds are broadly divided into two types (I and II) based on the presence or absence of nitrogen impurities, and further subdivided according to the arrangement of nitrogen atoms (isolated or aggregated) and the occurrence of boron impurities. Diamond type is directly related to color and the lattice defects that are modi- fied by treatments to change color. Knowledge of type allows gemologists to better evaluate if a diamond might be treated or synthetic, and whether it should be sent to a laboratory for testing. Scientists determine type using expensive FTIR instruments, but many simple gemological tools (e.g., a microscope, spectroscope, UV lamp) can give strong indications of diamond type. emologists have dedicated much time and critical to evaluating the relationships between dia- attention to separating natural from syn- mond growth, color (e.g., figure 1), and response to G thetic diamonds, and natural-color from laboratory treatments. With the increasing availabili- treated-color diamonds. Initially, these determina- ty of treated and synthetic diamonds in the market- tions were based on systematic observations made place, gemologists will benefit from a more complete using standard gemological tools such as a micro- understanding of diamond type and of the value this scope, desk-model (or handheld) spectroscope, and information holds for diamond identification. ultraviolet (UV) lamps. While these tools remain Considerable scientific work has been done on valuable to the trained gemologist, recent advances this topic, although citing every reference is beyond in synthetic diamond growth, as well as irradiation the scope of this article (see, e.g., Robertson et al., and high-pressure, high-temperature (HPHT) treat- 1934, 1936; and Kaiser and Bond, 1959).
    [Show full text]
  • Research Article Spectroscopic Characteristics of Treated-Color Natural Diamonds
    Hindawi Journal of Spectroscopy Volume 2018, Article ID 8153941, 10 pages https://doi.org/10.1155/2018/8153941 Research Article Spectroscopic Characteristics of Treated-Color Natural Diamonds 1 1 2 3 1 Meili Wang, Guanghai Shi , Joe C. C. Yuan, Wen Han, and Qing Bai 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, China 2Taidiam Technology (Zhengzhou) Co. Ltd., Zhengzhou, China 3National Gems & Jewelry Technology Administrative Center, Beijing, China Correspondence should be addressed to Guanghai Shi; [email protected] Received 15 October 2017; Accepted 28 December 2017; Published 7 March 2018 Academic Editor: Vincenza Crupi Copyright © 2018 Meili Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. With the increasing availability of treated-color diamonds on the market, their characterization is becoming more and more critical to the jewelry testers and customers. In this investigation, ten color diamonds treated by irradiation (4 pieces), HPHT (3 pieces), and multiprocess (3 pieces) were examined by spectroscopic methods. These diamonds are classified to be type Ia according to their FTIR characteristics. Using microscope and DiamondView, the internal features (such as distinctive color zoning and graphitized inclusions) and complex natural growth structures were observed, which show that the samples are more likely artificially colored natural diamonds. Through photoluminescence spectroscopy, a combination of optical centers was detected, − including N-V0 at 575 nm, N-V at 637 nm, H3 at 503 nm, H2 at 986 nm, and GR1 at 741 and 744 nm.
    [Show full text]
  • A History of Diamond Treatments
    AHISTORY OF DIAMOND TREATMENTS Thomas W. Overton and James E. Shigley Although various forms of paints and coatings intended to alter the color of diamond have likely been in use for almost as long as diamonds have been valued as gems, the modern era of dia- mond treatment—featuring more permanent alterations to color through irradiation and high- pressure, high-temperature (HPHT) annealing, and improvements in apparent clarity with lead- based glass fillings—did not begin until the 20th century. Modern gemologists and diamantaires are faced with a broad spectrum of color and clarity treatments ranging from the simple to the highly sophisticated, and from the easily detected to the highly elusive. The history, characteris- tics, and identification of known diamond treatments are reviewed. or as long as humans have valued certain mate- been long periods, both ancient and modern, when rials as gems, those who sell them have sought diamond treatments were conducted in the relative ways to make them appear brighter, shinier, open, and their practitioners were regarded by some Fand more attractive—to, in other words, make them as experts and even artists. Gem treatments, it must more salable and profitable. From the earliest, most be recognized, are neither good nor bad in them- basic paints and coatings to the most sophisticated selves—fraud comes about only when their presence high-pressure, high-temperature (HPHT) annealing is concealed, whether by intent or by negligence. processes, the history of diamond treatments paral- This fact places a specific responsibility for full treat- lels that of human advancement, as one technologi- ment disclosure on all those handling gem materials, cal development after another was called upon to and most especially on those selling diamonds, given serve the “King of Gems” (figure 1).
    [Show full text]
  • Diamond 1 Diamond
    Diamond 1 Diamond Diamond The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit. General Category Native Minerals Formula C (repeating unit) Strunz classification 01.CB.10a Identification Formula mass 12.01 g⋅mol−1 Color Typically yellow, brown or gray to colorless. Less often blue, green, black, translucent white, pink, violet, orange, purple and red. Crystal habit Octahedral Crystal system Isometric-Hexoctahedral (Cubic) Cleavage 111 (perfect in four directions) Fracture Conchoidal (shell-like) Mohs scale hardness 10 Luster Adamantine Streak Colorless Diaphaneity Transparent to subtransparent to translucent Specific gravity 3.52±0.01 Density 3.5–3.53 g/cm3 Polish luster Adamantine Optical properties Isotropic Refractive index 2.418 (at 500 nm) Birefringence None Pleochroism None Dispersion 0.044 Melting point Pressure dependent References Diamond 2 In mineralogy, diamond (from the ancient Greek αδάμας – adámas "unbreakable") is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells.
    [Show full text]
  • Color the Diamond Course
    Color The Diamond Course Diamond Council of America © 2015 Color In This Lesson: • The Surprising C • The Diamond Palette • Causes of Color • Evaluating Color • Grades and Descriptions • Demonstrating Color • Color, Rarity, and Value • Personalizing Color THE SURPRISING C Many customers today know that color affects a dia- mond’s value. However, they may not understand what the term “color” really means the way professionals nor- mally use it. They may also be puzzled by typical expla- nations on websites, in consumer literature, or from other retailers. As a result, there are a number of facts that can cause surprise when you discuss this C: • Diamonds occur in many colors. • Most diamonds are at least faintly tinted. • Truly colorless diamonds are rare. • Diamond color can be added or subtracted by Color is a less visible, less tangible factor to artificial treatments. most consumers. • Less color usually means higher value, but some- Photo courtesy William Schraft. times the opposite is true. • Small differences in color can make sizable differ- ences in price. • Color’s impact on beauty is highly personal. The Diamond Course 4 Diamond Council of America © 1 Color The challenge in presenting color is to keep these surprises from causing confusion. Instead, you need to use them to create positive results. With an effective explanation of color you can highlight the natural wonder of your product, demonstrate your knowledge and skill, illuminate one of the mysteries of value, and help your customer take a step toward a satisfying pur- chase decision. You’ll learn to do all those things in this lesson.
    [Show full text]
  • Color Grading “D-To-Z” Diamonds at the Gia Laboratory
    COLOR GRADING “D-TO-Z” DIAMONDS AT THE GIA LABORATORY John M. King, Ron H. Geurts, Al M. Gilbertson, and James E. Shigley Since its introduction in the early 1950s, GIA’s D-to-Z scale has been used to color grade the overwhelming majority of colorless to light yellow gem-quality polished diamonds on which lab- oratory reports have been issued. While the use of these letter designations for diamond color grades is now virtually universal in the gem and jewelry industry, the use of GIA color grading standards and procedures is not. This article discusses the history and ongoing development of this grading system, and explains how the GIA Laboratory applies it. Important aspects of this sys- tem include a specific color grading methodology for judging the absence of color in diamonds, a standard illumination and viewing environment, and the use of color reference diamonds (“mas- ter stones”) for the visual comparison of color. istorically, the evaluation of most gem dia- ence between G and H color for a one carat round- monds focused on the absence of color brilliant diamond of VS1 clarity was about 16% in (Feuchtwanger, 1867; figure 1). Today, this both Idex and Rapaport. Hlack of color is expressed virtually worldwide in a As part of its educational program, GIA has taught grading system introduced by GIA more than 50 the basics of color grading D-to-Z diamonds since the years ago that ranges from D (colorless) to Z (light early 1950s. And in the more than five decades since yellow). With the acceptance of this system, color the GIA Laboratory issued its first diamond grading grade has become a critical component in the valua- report in 1955 (Shuster, 2003), it has issued reports for tion of diamonds, leading to historic highs at the top millions of diamonds using the D-to-Z system.
    [Show full text]
  • NATURAL-COLOR BLUE, GRAY, and VIOLET DIAMONDS: ALLURE of the DEEP Sally Eaton-Magaña, Christopher M
    FEATURE ARTICLES NATURAL-COLOR BLUE, GRAY, AND VIOLET DIAMONDS: ALLURE OF THE DEEP Sally Eaton-Magaña, Christopher M. Breeding, and James E. Shigley Natural-color blue diamonds are among the rarest and most valuable gemstones. Gray and violet diamonds are also included here, as these diamonds can coexist on a color continuum with blue diamonds. More so than most other fancy colors, many diamonds in this color range are sourced from specific locations—the Cullinan mine in South Africa and the Argyle mine in Australia. Although blue color is often associated with boron impurities, the color of diamonds in this range (including gray and violet) also originates from simple structural defects produced by radiation exposure or from more complex defects involving hydrogen. These different mechanisms can be characterized by absorption and luminescence spectroscopy. A fourth mechanism—micro- inclusions of grayish clouds or tiny graphite particles in gray diamonds—can be distinguished through microscopy. In this article, we summarize prior research as well as collected data such as color and carat weight on more than 15,000 naturally colored blue/gray/violet diamonds from the GIA database (along with an analysis of spectroscopic data on a subset of 500 randomly selected samples) to provide an unprecedented description of these beautiful gemstones. iamond in its pure form would be an uncom- hibition at the Smithsonian. Several other historical plicated material to study scientifically: a blue diamonds are also steeped in legend and royalty Dperfectly assembled carbon crystal with no (see, e.g., Gaillou et al., 2010). Additionally, recently color, no structural imperfections or defects at the discovered stones (e.g., Gaillou et al., 2014) capture atomic lattice level, and no inclusions.
    [Show full text]
  • NATURAL-COLOR GREEN DIAMONDS: a BEAUTIFUL CONUNDRUM Christopher M
    FEATURE AR ICLES NATURAL-COLOR GREEN DIAMONDS: A BEAUTIFUL CONUNDRUM Christopher M. Breeding, Sally Eaton-Magaña, and James E. Shigley Among fancy-color diamonds, natural-color green stones with saturated hues are some of the rarest and most sought after. These diamonds are colored either by simple structural defects produced by radiation exposure or by more complex defects involving nitrogen, hydrogen, or nickel impurities. Most of the world’s current pro- duction of fine natural green diamonds comes from South America or Africa. Laboratory irradiation treatments have been used commercially since the late 1940s to create green color in diamond and closely mimic the effects of natural radiation exposure, causing tremendous difficulty in gemological identification. Compounding that problem is a distinct paucity of published information on these diamonds due to their rarity. Four different coloring mechanisms—absorption by GR1 defects due to radiation damage, green luminescence from H3 de- fects, and absorptions caused by hydrogen- and nickel-related defects—can be identified in green diamonds. Careful microscopic observation, gemological testing, and spectroscopy performed at GIA over the last decade allows an unprecedented characterization of these beautiful natural stones. By leveraging GIA’s vast database of diamond information, we have compiled data representative of tens of thousands of samples to offer a look at natural green diamonds that has never before been possible. ancy-color diamonds are among the most highly researchers, however, have had the opportunity to ex- valued of gemstones due to their beauty and rar- amine large quantities of similarly colored natural di- Fity. Interestingly, the rarest of diamond colors amonds and report on their distinctive characteristics.
    [Show full text]