FINDING A by wuyunyi


									                                                                                   FINDING A

                                                                                   The lab may replace

                                                                                   the loupe as treatments
                                                                                   of diamonds and colored

                                                                                   gemstones increase.


                                                                                                                      istorically, handshakes and honor seal million-dollar

                                                                                                               H      gem deals around the world, but on the streets of
                                                                                                                      Chanthaburi, Thailand, nothing is returnable, re-
                                                                                                               gardless of defect or misrepresentation. The best defense
                                                                                                               against fraud in this center of colored stone trade is pay-
                                                                                                               ing with a postdated check.
                                                                                                                  The average person cannot spot a fake, let alone a real
                                                                                                               stone that has been enhanced. Gemologists, appraisers,
                                                                                                               and jewelers routinely use simple tools—such as a jewel-
                                                                                                               er’s loupe, microscope, or solutions of known refractive
                                                                                                               index—to reveal more about a stone. But as enhance-
                                                                                                               ments become more difficult to detect, even experts are
                                                                                                               increasingly dependent on analytical chemistry to defend
                                                                                                               the integrity of their trade against aggressive tampering.
                                                                                   Rachel A. Petkewich

                                                                                                                             F E B R U A R Y 1 , 2 0 0 3 / A N A LY T I C A L C H E M I S T R Y   71 A
                                    What is a gem?                                                                      perfections called inclusions and marketplace comparisons to
                                    Gems are cut and polished stones, such as diamonds, pearls, and                     grade and certify stones. “Gemology—in comparison to other
                                    colored stones, including sapphires, tourmalines, opals, and tan-                   industries—is still in the dark ages,” says Cap Beesley, president
                                    zanite. The term “fake” is reserved only for glass or plastic sub-                  of American Gemological Laboratories in New York City. His
                                    stitutes. Buyers may encounter synthetics, which are grown in a                     lab developed a series of seminars that introduce more advanced
                                    lab but have the exact same chemical formula, hardness, and spe-                    instrument technologies to the gemological community, so that
                                    cific gravity as the corresponding natural gems, or simulants, which                people start thinking beyond the traditional microscope, re-
                                    look like their respective gems but do not have the same chemical                   fractometer, and polariscope.
                                    properties. Cubic zirconia (zirconium silicate) and moissanite
                                    (silicon carbide) are examples of common diamond simulants.                         Analyze this
                                        Even natural gems may not be pristine. Poor-quality mate-                       Labs may be foreign territory for gemologists, but gemstones are
                                    rials may be treated to garner a higher price. Heating or irradi-                   not strangers to analytical chemists. For example, corundum—
                                    ation may improve color and clarity by altering the internal chem-                  the basic mineral name of the Al2O3 structure for ruby and
                                                                                                                        sapphire—is a key component of electronics and lasers used in
                                                                                                                        military equipment and scientific research and one of the world’s
                                                                                                                        20 most studied materials. Scientists have always synthesized
                                                                                                                        stones for lasers. As the techniques for creating these stones im-
                                                                                                                        proved, and the defense research programs collapsed in places
                                                                                                                        like the former Soviet Union, jewelry became a secondary mar-
                                                                                                                        ket for synthetic gems, recalls Daniel Armstrong, a chemist at
                                                                                                                        Iowa State University.
                                                                                                                            Despite all the study, there is still a lot to learn about syn-
                                                                                                                        thesizing stones. Growing gem crystals is still a bit of “black art”,
                                                                                                                        because knowing the stoichiometry of one gem is not necessarily
                                                                                                                        the recipe for creating another, according to Thomas Chatham,

                                                                                                                        president of the prominent U.S. synthetic gemstone company
                                                                                                                        Chatham Created Gems, Inc.
                                                                                                                            Geologists and solid-state chemists can explain some miner-
                                                                                                                        al formation and colors with established theories, but they use
                                                                                                                        analytical techniques to learn more. Transition-metal activity
                                                                                                                        governs most mineral chemistry in accordance with interva-
                                                                                                                        lence charge transfers, element substitution, and crystal field
                                                                                                                        theories. Therefore, temperature and pressure strongly influence
                                    Creating clarity.                                                                   color and clarity as a colored stone develops or is chemically al-
                                    Natural cracks and fissures in emeralds are often filled with oils and resins to
                                                                                                                        tered. “In gemological methods, modern high-tech methods
                                    increase the value of a stone. Over time, the fillers can dissolve from the stone   are certainly applicable and absolutely needed—IR, UV, lumines-
                                    or, as shown here, become cloudy.                                                   cence, energy-dispersive X-ray fluorescence, radioactive count-
                                                                                                                        ing technologies,” says George Rossman, a mineralogy profes-
                                    istry of a stone, but these treatments can make some stones more                    sor at the California Institute of Technology. “In an academic
                                    brittle or result in an undesirable color change. For example,                      environment, [we] are not approaching the everyday problems
                                    many pearls and some colored stones were unknowingly altered                        of the gem industry but more the fundamental basics of color
                                    when the U.S. Postal Service began irradiating mail to elimi-                       in minerals from a [purely] scientific point of view, and we need
                                    nate potential anthrax attacks. Adding oils, resins, or waxes to                    even a higher level of sophistication.”
                                    mask significant fissures and cracks will improve a stone’s clar-                       Adapting nondestructive analytical techniques to less-than-ideal
                                    ity and increase its price tag. Nevertheless, some synthetics and                   situations has been a challenge for all. “People who owned gem-
                                    treatments have become acceptable to consumers—provided                             stones objected to grinding them to a powder or dissolving
                                    they know what they are buying.                                                     them in solution for a good analysis,” so UV–vis, IR, and Raman
                                        Although professional gem organizations have established                        data collected with standard equipment is precluded, says Arm-
                                    guidelines for stone certification, the nomenclature that de-                       strong. Gem thickness, facets, and jewelry settings mean that
                                    scribes certain newer treatments remains a hotly contested sub-                     light “doesn’t necessarily travel in a nice straight line from the
                                    ject. Gemologists may use scientific analysis to determine                          light source to the detector, so you have to learn to live with these
                                    chemical structure and composition, but the traditional meth-                       things and compensate for them,” he adds. He and Beesley col-
                                    ods to evaluate stones don’t use modern technology and are                          laborated on work with near-IR and a diffuse reflectance FTIR
                                    still subjective. For example, gemologists use small, natural im-                   device that helped consistently detect polymers, oils, and waxes

                                    72 A     A N A LY T I C A L C H E M I S T R Y / F E B R U A R Y 1 , 2 0 0 3

                 used for filling imperfections in notoriously fragile beryl minerals,                  However, he explains,
                 such as emeralds. Although methods such as elemental analysis,                         if you heat the stone
                 secondary ion MS (SIMS), laser ablation, and electron micro-                           to 1600–1800 °C, the
                 probes can be destructive, they are also used to help establish                        TiO2 will dissolve into
                 composition.                                                                           the Al2O3 structure,
                                                                                                        and “it could be 100          (b)
                 The “corundum conundrum”                                                               million years before
                 Tied to a history of myths and legends, certain stones are be-                         [reprecipitation] is
                 lieved to ward off evil spirits and temptation or bring good luck                      noticeable.” Although
                 while others can end up worth more in memories than money.                             people still take their
                 Sapphires are the latest example.                                                      chances with primitive

                                                                                                                                                                                                    (A) THOMAS CHATHAM; (B) AND (C) AMERICAN GEMOLOGICAL LABORATORIES
                     Rubies and sapphires have been heated for centuries, but                           furnaces, stones are
                 primitive furnaces did not produce enough heat to significant-                         frequently heated in a
                 ly change them. Furnaces today are much more sophisticated,                            sensor-controlled en-
                 says Richard Hughes, an author and gemologist for gem                                  vironment because
                 wholesaler Pala International in California. For example, in the                       color and clarity will        (c)
                 mid-1960s, some gem treaters from Thailand discovered that                             change with variations
                 previously worthless stones lining driveways in Sri Lanka could                        in oxygen partial pres-
                 be heated to near melting and brought from “brand X to killer                          sure and the ratio of
                 colors” with “zip to significant value,” adds Beesley. “It was an                      iron oxidation states.
                 alchemist’s dream.”                                                                        Diffusing any for-
                     Treatments are becoming more complex because, as Chatham                           eign material other
                 says, “In the last decade, [treaters] brought in the chemists.”                        than hydrogen into a
                 Rubies are red—and rare—primarily due to a small amount of                             stone during heating
                 chromium in the crystal lattice. Iron and titanium content are                         creates controversy in
                 responsible for the color of blue sapphires, and other trace com-                      gemology. Hughes                  Inclusions in colored stones.
                 binations explain other, less-common colors of sapphires. Rossman                      dubbed research into              Gemologists and appraisers look for
                                                                                                        the latest treatment              natural imperfections called inclu-
                                                                                                        the “corundum co-                 sions to grade gemstones. (a) These
                                                                                                        nundrum”. It started              needles are never seen in synthetic
                                                                                                                                          rubies; (b) heating would remove this
                                                                                                        with padparadscha, an
                                                                                                                                          “silk” from a natural sapphire, but
                                                                                                        extremely rare, pink-             might change (c) the solid, liquid, and
                                                                                                        ish-orange sapphire               gas phases of this emerald.
                                                                                                        named for the exotic
                                                                                                        color of lotus blos-
                                                                                                        soms, but has spread
                                                                                                        to other colors of sap-
                                                                                                        phire. Vast quantities of orange stones started to appear in Thai
                                                                                                        and Japanese markets in 2001. Looking at a cross section, Ken
                                                                                                        Scarratt, director of the American Gem Trade Association
                                                                                                        (AGTA) Gemological Testing Center, noticed a yellow rim on a

                                                                                                        pink stone, which explains why it appeared to be orange. Mada-
                                                                                                        gascar pink sapphire retails for approximately $1000 a carat,
                                                                                                        whereas natural padparadscha can sell for up to $25,000. James
                                                                                                        Shigley, the director of research at the Gemological Institute of
                 Diamonds in the rough.                                                                 America (GIA) based in California, says the labs “have been try-
                 Synthetic stones, such as these rough white, pink, and yellow diamonds, have all
                                                                                                        ing to understand the treatment process in a way that there is
                 of the chemical and physical properties of a natural stone, but were grown in a lab.   some scientific integrity,” so they called on corundum expert
                                                                                                        John Emmett, who, with Troy Douthit, started a small compa-
                 says heating intensifies the color of a blue sapphire by “tailor-                      ny called Crystal Chemistry in Brush Prairie, Wash. after retiring
                 ing the ratio of Fe(II) to Fe(III) to optimize the intervalence                        as the associate director responsible for laser development at
                 charge transfer.” TiO2, which occurs naturally in sapphires, can                       Lawrence Livermore National Laboratory.
                 precipitate out to form myriads of microscopic crystals in the                             Emmett was confident that “the only way you can get those
                 Al2O3 structure, making the gem appear cloudy, milky, or turbid.                       rims is by diffusion [of a foreign element like beryllium], and dif-

                                                                                                                        F E B R U A R Y 1 , 2 0 0 3 / A N A LY T I C A L C H E M I S T R Y   73 A
                                                                                                                 Hughes warns that the “diamond industry will experience some
                                                                                                                 serious challenges distinguishing treated from pristine stones over
                                                                                                                 the next 5–10 years—including everything from the wedding ring
                                                                                                                 to the dramatic stones in museums.” Jewelers can use thermal
                                                                                                                 conductivity testers to distinguish real diamonds (tester shows a
                                                                                                                 green light) from simulants (red light), but not from treated dia-
                                                                                                                 monds (green light). The U.S. Federal Trade Commission (FTC)

                                                                                                                 requires that all synthetics and treatments be labeled by sellers and
                                                                                                                 maintains guidelines for gems (
                                                                                                                 gd.htm). However, Robin Spector, a lawyer with the FTC, says
                                                                                                                 they have received very few consumer complaints about misrep-
                                                                                                                 resentation in marketing and advertising that involve jewelry.
                                                                                                                     “The gem business is not all about scandals—it is about bring-
                                                                                                                 ing very rare and beautiful things to market and has a history
                                                                                                                 going back thousands of years,” reminds Hughes. But even if rel-
                                    Refractive index solutions reveal treated sapphires.                         atively cheap analytical techniques were available to verify quality,
                                    Natural orange sapphires should “disappear” when immersed in di-
                                                                                                                 the reputation of certain stones may not be saved. For example,
                                    iodomethane because the naked eye cannot distinguish between two             so much blue topaz was treated in the past that the bottom fell
                                    materials of the same refractive index. This cross section of a treated      out of the market. Now, the trade just assumes that all blue topaz
                                    orange sapphire viewed in immersion is typical of those that have cre-       is treated, so the stones are cheap. Gemologists say the Internet
                                    ated the recent controversy. Here, the obvious orange rim exactly con-
                                                                                                                 helped quickly alert the trade to the scientific findings for the or-
                                    forms to the surface contours of the gem surrounding a pink core, but
                                    the orange color may penetrate all the way through some stones.              ange stones, though it did not help the dealers who paid huge
                                                                                                                 amounts of money for stones that no one will buy.

                                                                                                                 More treaters than testers
                                                                                                                 Shigley says requests for analytical confirmations from gemolo-
                                    fusion is a dirty word in the gem business.” He based his conclu-            gists are increasing. “We find that there are more and more sub-
                                    sion on previous experience using SIMS results to explain the nat-           tle differences to check for to identify synthetic and treated
                                    ural occurrence of orange spots in blue sapphires from Montana;              gems.” Although Emmett advised AGTA and GIA to do sys-
                                    in that case, divalent impurities exceeded tetravalent impurities and        tematic SIMS and laser ablation studies to better understand the
                                    essentially trapped holes that would absorb light differently than           trace-element chemistry in the sapphires, he says, “There is no
                                    the rest of the stone. First, to prove beryllium could diffuse into          money to do gemological research like there is if you are work-
                                    corundum and create a trapped hole center that makes a pink                  ing on laser materials.” Hughes says even raising $15,000 to test
                                    stone look orange, he created yellow rims on pink sapphires. Sec-            the orange stones was “very hard.” Emmett will likely pay for ad-
                                    ond, SIMS tests of the rims on sapphires found in Thai and Japan-            ditional laser ablation and inductively coupled plasma MS work
                                    ese markets showed 10–30 ppm of beryllium. Emmett says beryl-                “just to satisfy [his] curiosity.” Armstrong says government fund-
                                    lium could occur naturally in any sapphire, but even 1 ppm “is an            ing is limited because “it is not considered ultrabasic science, or
                                    extraordinary find,” so the results confirmed that “millimeter-type          it doesn’t have a direct effect on health or energy or defense.”
                                    depths” of yellow on pink stones was an intentional treatment.               Beesley adds, “In gemology, there are very few individuals with
                                        After spectroscopy results concurred, gemologists were con-              deep pockets interested in funding even basic research to stimu-
                                    vinced about the treatment process and began to alert the trade.             late a deeper understanding of the gem sciences.”
                                    Thai traders who sold the stones initially denied intentional dif-               “Every jewelry store in the nation cannot have a quarter-million-
                                    fusion, but Hughes says “[the labs] have no question about it.”              dollar IR spectrometer with cryogenic accessories or scanning elec-
                                    American and European markets were largely unaffected be-                    tron microscopes,” Rossman says, so jewelers need quick, conven-
                                    cause buyers were alerted in time. However, orange stones are                ient analysis using refractive index, density measurements, and
                                    much more popular in Japanese markets. They were flooded                     conductivity. Beesley and Armstrong believe that the gem industry
                                    with treated stones that had been mistakenly certified as natural.           can probably afford miniaturized analytical instruments and plan to
                                        Hughes says people have incentive to create new treatments if            create specialized prototypes. Beesley says, “No matter what new
                                    the trade puts treated stones alongside high-grade, natural stones           treatments are developed, the answer is trapped in the material—it
                                    in the market. He is one of many gemologists who fear analytical             is simply choosing the technique and methodology to identify it.”
                                    chemistry may be the only way to examine diamonds and colored                Although the concept may ruin the mystique of gem trading, a field
                                    stones in the future. Even some large companies are trying to                instrument should protect buyers better than postdated checks.
                                    make the most of undesirable yellow and brown diamonds, which
                                    are colored because nitrogen gets trapped during formation.                  Rachel Petkewich is an assistant editor of Analytical Chemistry.

                                    74 A    A N A LY T I C A L C H E M I S T R Y / F E B R U A R Y 1 , 2 0 0 3

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