Fingerprinting Diamonds

Diamonds may be a girl's best friend, but for the police they are a major nuisance. Once they are stolen, they are among the easiest of valuables to sell. Even if they are recovered, the four Cs of the diamond business--cut, clarity, carat and color--provide only the roughest means of identification. In fact, identification is sometimes so difficult that police have occasionally been forced to return diamonds to a known thief because there was no proof that they were stolen goods. Now, Israeli scientists think they have solved the gem identity crisis with a system that they claim is as infallible as fingerprinting.

The idea for a so-called gemprinting technique grew out of a chance conversation between Physicist Shmuel Shtrik-man and an old friend, Meyer Kaplan, head of the criminal identification division of the Israeli Ministry of Police. While describing his work at the Weizmann Institute, Shtrikman complained that each of the diamonds he was using in his experiments produced a unique pattern when a beam of light was reflected from it onto a screen. Aware that Israel is the world's largest exporter of cut diamonds, Kaplan suggested that the patterns might be used to identify individual gems.

Shtrikman and his Weizmann team soon developed a simple diamond-identifying device. It consists of a small helium-neon laser that directs a beam of light through a pinhole in a sheet of Polaroid film and onto a diamond. As the laser's uniform light waves hit the "table" (or top facet) of the gem, some of them are reflected. Others enter the diamond, circle around inside it and are refracted at varying angles. The result is a unique pattern of spots on the film that looks like a bright, star-cluttered sky; in more advanced versions of the system, the spots turn into a pattern of concentric circles because the diamond is rotated during exposure. Says Shtrikman: "Diamonds are like people. No two are alike. Every diamond, even the purest, has specific impurities, stains and flaws. Even the smallest difference between stones can cause a completely different print." Only if the diamond is cut up into smaller gems--often difficult to do unless the original stone is quite large--or if some of its facets are repolished will the distinctive identifying information be lost.

Act of Faith. Now manufactured commercially by Kulso Ltd., the machine (cost: about $3,500) can produce an identifying print in two minutes. Shtrikman believes that the patterns, which show brilliancy and quality of a cut stone as well, can also be used to assess a diamond's value. That innovation could have even greater impact on gem transactions. Until now, the only real assurance diamond traders have had when they concluded a deal was the traditional act of faith between them: a handshake and the exchange of the Hebrew words "mazal u-brocha" (luck and a blessing).

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