[Jewelry making - Article 00831] - [Orchid] New gem ID technique

[Steelybone]

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    Excerpt from New Scientist: newscientist.com 

    Colour profile exposes faked or stolen gems - Anna Gosline 

          Jewellers say that every gemstone is unique, and soon they may
          be able to prove it. That will make it easier to recover lost
          or stolen gems, even after they are cut or altered. 

          The jewellery industry has long looked for ways to establish a
          gemstone's type and quality, and to spot fakes. But
          identifying individual stones is difficult because there are
          so many, and the good ones are quite similar. 

          Now a technique dubbed "microspectrometry" could change that,
          by mapping the unique colour patterns of each gem. Mike Eyring
          of the Arizona Department of Public Safety and Paul Martin of
          CRAIC Technologies in Altadena, California, both in the US,
          measured the spectra of the ultraviolet and visible light
          absorbed by three sapphires and three lower-value red stones
          called spinels, often used in place of rubies. Sapphires get
          their blue colour from charge transfer between iron ions.
          Spinels, like rubies, glimmer red from chromium impurities. 

          Ultraviolet "fingerprint" 

          The researchers recorded the spectrum emitted by a
          10-micrometre-wide point on each stone's surface and found
          that every one, even those of the same type, had a different
          spectrum. The differences were particularly marked in the
          ultraviolet range. "That could be your fingerprint," says
          Martin, who presented his results at the American Academy of
          Forensic Sciences meeting in New Orleans, US, last month. 

          George Rossman, a mineralogist at the California Institute of
          Technology, US, is sceptical of the claim that every gem's
          spectrum will be different. But mapping the variations in
          colour, he says, could provide useful information. "The
          question that needs to be researched is whether this tool adds
          enough to what is out there already," he says. 

          The Gemological Institute of America, for example, grades
          gemstones by generating maps of each one's flaws, as well as
          recording their cut, carat weight and clarity. Every
          measurement is added to a database, and stolen stones have
          often been identified after being resubmitted for grading.

Tas


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