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Fall 1981 Gems & Gemology

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Fall 1981 Gems & Gemology VOLUME XVII FALL 1981 . quarterly journal of the Gemol~gica~lInstitute ot merica FALL 1981 Volume 17 Number 3 TABLE OF CONTENTS FEATURE 121 Heat Treating Ruby and Sapphire: Technical Aspects ARTICLES IZ~lrtNassttu 132 Photographing Inclusions John I. Koiviila 143 Cryogenics, an Aid to Gemstone Testing Stephen C. Hofer and D. Vincent Manson NOTES 150 Revolution in Diamond Cutting: Laser Sawing of Diamond Crystals AND NEW David M. Baker TECHNIQUES 153 Ruby in Diamond Henry 0. A. Meyer and Edward Gubelin 157 The Andradites of San Benito County, California Tedd Payne REGULAR 161 Gem Trade Lab Notes FEATURES 167 Gemological Abstracts 179 Book Reviews 180 Gem News ABOUT THE COVER: As many of the illustrations in this issue demonstrate, inclusions often provide significant, if not unique, clues to the identity of a gemstone and the orisins of its color and other characteristics. Inclusion photography, therefore, can also play an important role in gemology-and, as is evident in this cover photograph, an aesthetically pleasing one as well. Included in quartz, framed by iridescent stress fractures, this euhedral spessarline garnet crystal testifies to the pegmatitic origin of its host. Magnified 60x.Photograph by John I. Koivula. Composition for Gems & Gemology is by Printed Page Graphics, Fullerton, CA. The color separations are by Effective Graphics, Compton, CA. Printing is by Waverly Press, Easton, MD "-1981 Gemological Instilute of America. All rights reserved. ISSN 0016-62X EDITORIAL Editor-in-Chief Managing Editor Editor, Gem Trade Lab Notes STAFF Richard T. Liddicoat, Jr. Alice S. Keller Chuck Fryer Associate Editor 1660 Stewart St. Editor, Geniological Abstracts Peter C. Keller Santa Monica, CA 90404 Dona M. Dirlarn Telephone: (213) 829-2991 Associate Editor Editor, Book Reviews D. Vincent Manson Subscriptions Manager John I. Koivula Janet M. Fryer Contributing Editor Editor, Gem News John 1. Koivula Stephanie Dillon PRODUCTION Art Director Cover Design GIA Photographers STAFF Susan Kingsbury Peter Johnston Mike Havstad Tino Hammid EDITORIAL Robert Crowningshield Anthony R. Kanipf Glenn Nord REVIEW BOARD New York, NY Los Angeles, CA Los Angeles, CA Pete Dunn John Koivula Rick Shaw Washington, DC Son to Monica, CA Santa Monica, CA Dennis Foltz Sallie Morton John Sinkankas Santa Monica, CA San Jose, CA San Diego, CA Chuck Fryer Kurt Nassau George Rossnx~n Santa Monica, CA Bernardsville, N[ Pasadena, CA C. S. Hurlbut, Jr. Cambridge, MA SUBSCRIPTIONS Subscriptions in the U.S.A. are priced as follows: $16.50 for one year (4 issues), $45.00 for three years (12 issues). Subscriptions sent elsewhere are: $25.00 for one year, $65.00 for three years. Special annual subscription rates are available for all students actively involved in a GIA program: $12.00 U.S.A., $20.00 elsewhere. Your student number must be listed at the time your subscription is entered. Single issues may be purchased for $5.00 in the U.S.A., $7.00 elsewhere. A limited number of back issues of G&G are also available for purchase. Please address all inquiries regarding subscriptions and the purchase of single copies or back issues to the Subscriptions Manager. MANUSCRIPT Gems s) Gemology welconles the submission of articles on all aspects of the field. Please see the Suggestions for SUBMISSIONS Authors for preparing manuscripts in the Summer 1981 issue of the journal or contact the Managing Editor for a copy. Letters on articles published in Gems ed Gemology and other relevant matters are also welconle. COPYRIGHT Abstracting is permitted with credit to the source. Libraries are permitted to photocopy beyond the limits of U.S. AND REPRINT copyright law for private use of patrons. Instructors are permitted to photocopy isolated articles for noncon~n~ercial PERMISSIONS classroon~use without fee. For other copying, reprint, or republication permission, plcasc contact the Managing Editor. Gems 01 Gemology is published quarterly by the Gemological Institute of America, a nonprofit educational organization for the jewelry industry, 1660 Stewart St., Santa Monica, CA 90404. Any opinions expressed in signed articles are understood to be the views of the authors and not of the publishers. HEAT TREATING RUBY AND SAPPHIRE: TECHNICAL ASPECTS By Kurt Nassau Ruby and sapphire of natural or synthetic n recent months, a variety of heat-treated sapphires origin can be heat treated to improve I and rubies with gemological characteristics different asterism; to remove asterism or silk; to from any previously seen have appeared on the market. improve, add, or remove color; and even Contradictory rumors abound regarding the different to alter imperfections. At least nine manners and methods of treatment. distinct processes can be identified, Examples of heat treatment methods that have been although several may occur simultaneously. Some of these treatment used to improve the appearance of gemstones include the methods correspond to natural processes conversion of green aquamarine to blue; the "pinking" of and may not leave any evidence of their brown chromium-containing topaz; the "crackling" of use; others do not correspond to natural quartz; the reddening of yellow agate, carnelian, and processes and are readily identifiable. tiger's-eye; the development of the blue color of tanzan- ite; and the conversion of amethyst to citrine or to "greened amethyst." Such processes may be termed heat- ing, burning, annealing, firing, high-temperature soaking, and so on. The use of these types of heat treatment is usually not specified. The reaction of synthetic corundum (Nassau, 1980a) to various types of heat treatment has been studied widely, and the results are equally applicable to the natural ma- terial. Although most of the treatment methods described here have been known for some time, their use to im- prove rubies and sapphires has become widespread only recently. The important parameters in any type of heat treat- ment are: 1. The temperature-time relationship ABOUT THE AUTHOR 2. The oxidation-reduction conditions Dr. Nassau is a research scientist residing in 3. The presence of chemical substances that can in- Bernardsville, NJ, He does not wish to be contacted on any aspect of this article. teract with the gemstone Acknowledgments: The author is grateful to Heat treatment of corundum can affect the presence of Robert Crowningshield, of the GIA Gem Trade milkiness and asterism, the color, and even the internal Laboratory in New York, for helpful discussions; structure (inclusions as well) of the material. A number and to Robert E. Kane, of the GIA Gem Trade Laboratory in Los Angeles, for gathering the of separate processes have been distinguished, although illustrations and writing the figure legends, several may be performed simultaneously. The exact %'I981Gemological Institute of America temperature, duration of treatment, and chemicals used Heat Treating Ruby and Sapphire GEMS & GEMOLOGY Fall 1981 121 for each process will depend on the specific ma- PROCESS 1: terial being heated; considerable variation must DEVELOPMENT OF be expected with corundum from different lo- POTENTIAL ASTERISM calities. Some natural sapphire and ruby, as well as some Nine possible treatment modes are summa- synthetic material intended for star use, contains rized in table 1 and examined in turn below. Iden- a significant amount of titanium oxide. If such tifying characteristics of such treatment methods corundum cools fairly rapidly from its growth have been discussed in detail by Crowningshield conditions, the material remains clear; the tita- and Nassau (1981);therefore, they will be touched nium oxide is in "solid solution" in the form of on here only briefly. Tifi (titanium sesquioxide) replacing some of It should be noted that no consensus has yet the A120y(aluminum oxide). been reached as to whether any of these types of If such material, which typically contains only treatment need to be disclosed to the buyer. The a few tenths of a percent titanium oxide, is held parallel is sometimes drawn that since heat treat- at between llOO° and 1500° for some time ment is not customarily disclosed with other (say, 1300° for 24 hours), particularly under gemstones, such as heated blue aquamarine, why mildly oxidizing conditions, the TizOg converts should such disclosure be necessary with sap- to TiOz (titanium dioxide) as follows: phires and ruby? There may be validity in viewing some types of treatment in this way, especially those that mimic natural processes (as is the case with aquamarine). However, other treatment In most cases, the TiOz will then form needles of methods-diffusion in particular-do not have rutile within the corundum and thus produce as- any parallel in nature. The results of diffusion terism. This process, which was patented for Linde treatment, for example, are readily recognized, Air Products Company by Burdiclz and Glenn and remind one more of Lechleitner synthetic (1949))is used to create all synthetic stars in co- emerald overgrowth on a natural beryl than of rundum (Nassau, 1980a), and the analogous pro- heated aquamarine. cess also occurs in nature. In fact, if a piece of TABLE 1. Heat treatment processes used on sapphires and rubies Treatment Specific group processa Result Heating only 1. Moderate temperature Develops potential asterism (130OoC) 2. High temperature Removes silk and asterism (160OoC), rapid cooling 3. Reductive heating Develops potential blue color (16OO0C) 4. Oxidative heating Diminishes blue color (16OO0C) 5. Extended heating Diminishes Verneuil banding (1800°C and strain Heating under unknown 6. ? Introduces fingerprint conditions inclusionsb Diffusion of impurities into 7. Add TiO, Produces asterismb the material (extended 8. Add Ti02 and/or Fe203 Produces blue colorb heating at 1800°C 9. Add Cr203,NiO, etc. Produces other colorsb ^Treatments 1 through 4 correspond to processes that also occur in nature; treatments 5 and 6 are used on synthetic material; treatments 7 through 9 do not correspond to natural processes. The temperatures given are representative only and will depend on the nature of the material and the length of time they are used.
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