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The Fingerprint of a Diamond

19.05.2014

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William Levine (center), a prominent American diamond merchant, inspecting gemprints during his visit to the Weizmann Institute in 1974, with Prof. Shmuel Shtrikman (left) and Dr. Charles Bar-Isaac (right)
 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Dr. Charles Bar-Isaac was in love when he traveled from Israel to Iran in the early 1970s: His goal was to meet the family of his future wife, Lillian. But in Teheran, Bar-Isaac, then a student at the Weizmann Institute of Science, encountered his second love. When visiting the exhibition of Iran’s crown jewels in the national bank, he was dazzled by the display of spectacular diamonds, among them the more than 3,000 diamonds studding the Pahlavi Crown and the world’s largest uncut diamond called The Sea of Light. Upon returning to Rehovot, he decided to focus his doctoral research on diamonds.
 
Lillian’s pendant. A turquoise inset is surrounded by 20 small diamonds
 
The Iraqi-born Bar-Isaac, who had immigrated to Israel with his parents at age six in 1950, earned a master’s degree in physics from the Hebrew University of Jerusalem before embarking on Ph.D. studies in what was then the Weizmann Institute’s Electronics Department, under the supervision of Profs. Shmuel Shtrikman and David Treves. In his doctoral thesis, he applied laser technologies and the principles of the area of physics known as Fourier optics to the study of diamonds. What attracted him to these gems was not just their beauty; he was fascinated by the physics of the aesthetic experience: How beauty is revealed by the light interacting with the precious stone.
 
It is the light reflected, refracted, dispersed and absorbed by a stone that determines such crucial properties as the gem’s brilliance and color. Diamonds stand out in their brilliance among all other gems because when exposed to light, they sparkle from virtually every angle. Throughout history, diamond cutters and jewelers sought out, by trial and error, the best ways to cut and polish the stones, until in 1919 in London, a young mathematician and physicist, Marcel Tolkowsky, developed a mathematical formula for cutting diamonds in an optimal manner. The process, which calls for cutting 58 facets on a diamond to provide maximum reflected light and brilliance, came to be known as the “ideal cut.” Today, most diamonds in the world are cut according to this principle. When Bar-Isaac started looking into the science behind the “ideal cut,” he was amazed to discover that even though the diamond industry had existed since biblical times – in the Book of Exodus, Moses is instructed to make a breastplate set with diamonds among other gems – several of its central issues had remained unresolved. One major issue, for instance, was how to definitively establish the identity of a particular diamond – a task that becomes especially crucial in police work when stolen diamonds are recovered, or in the frequent disputes between jewelers and customers who claim the stone returned after setting and cleaning is not the same one they left.  
 
Using as a model the exquisite diamond-framed pendant that Lillian had received from her mother, Bar-Isaac realized that the light scattered by each diamond carries a deal of information about the stone. That was how he came up with the idea for Gemprint: an optical system for “fingerprinting” diamonds by recording the angles and intensities of the reflected light rays, which form distinctive patterns. Since no two stones – no matter how similar they may look – create the same pattern, a comparison of their “fingerprints” can serve for positive identification.
Calculated gemprints, created by computerized ray tracing, reveal the difference between different cuts
 

 

In the system, a low-density laser beam shines upon a gem; its reflection pattern is then digitized and stored. Apart from positive identification, the method provides a means of quantifying beauty: It assigns measurable values to a diamond’s brilliance and can therefore be used in its grading – that is, establishing its quality. It can also help determine whether the diamond had been produced according to the ideal cut.
 

After registering a patent for Gemprint in the mid-1970s, Yeda Research and Development Co. Ltd., the Weizmann Institute’s technology transfer arm, licensed the system for commercial manufacture in Israel and elsewhere. Within a few years, Gemprint came into wide use in the diamond industry.

Two gemprints of the same stone, taken at different times, reveal themselves as identical when they are superimposed
 
Bar-Isaac decided not to continue scientific research after completing his doctorate in 1975, opting instead for a career in photography. He then left Israel, ultimately settling in London with Lillian and their three children.
 
As for Gemprint, the Weizmann Institute patent has in the meantime expired, but the system continues to be used around the world by diamond dealers, jewelers, insurers and professional appraisal services. Accepted as evidence of a gem’s identity in courts of law, it has helped to obtain convictions and return numerous lost or stolen diamonds to their rightful owners. International databases that hold the information about hundreds of thousands of diamonds are continuously being expanded with the gemprints of new precious stones.   
 

 
 
 
 

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