[Jewelry making - Article 00989] - [Orchid] 2500 BC diamonds for polishing

[L. Wright]

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    Some may find this article from Harvard of interest - Chinese used
    diamonds to polish sapphire-rich stone in 2500 BC 

    Laurie
    http://www.designerbeads.com


          Chinese used diamonds to polish sapphire-rich stone in 2500 BC 
          http://www.eurekalert.org/pub_releases/2005-02/hu-cud021105.php

          Find provides evidence of earliest known use of diamond and
          sapphire by prehistoric people 

          CAMBRIDGE, Mass. -- Researchers have uncovered strong evidence
          that the ancient Chinese used diamonds to grind and polish
          ceremonial stone burial axes as long as 6,000 years ago -=96 and
          incredibly, did so with a level of skill difficult to achieve
          even with modern polishing techniques. The finding, reported
          in the February issue of the journal Archaeometry, places this
          earliest known use of diamond worldwide thousands of years
          earlier than the gem is known to have been used elsewhere. 

          The work also represents the only known prehistoric use of
          sapphire: The stone worked into polished axes by China's
          Liangzhu and Sanxingcun cultures around 4000 to 2500 BC has as
          its most abundant element the mineral corundum, known as ruby
          in its red form and sapphire in all other colors. Most other
          known prehistoric artifacts were fashioned from rocks and
          minerals no harder than quartz. 

          "The physics of polishing is poorly understood; it's really
          more an art than a science," says author Peter J. Lu, a
          graduate student in physics at Harvard University's Graduate
          School of Arts and Sciences. "Still, it's absolutely
          remarkable that with the best polishing technologies available
          today, we couldn't achieve a surface as flat and smooth as was
          produced 5,000 years ago." 

          Lu's work may eventually yield new insights into the origins
          of ancient China's trademark Neolithic artifacts, vast
          quantities of finely polished jade objects. 

          Lu began the research in 1999, as a Princeton University
          undergraduate. He studied four ceremonial axes, ranging in
          size from 13 to 22 centimeters, found at the tombs of wealthy
          individuals. Three of these axes, dating to the Sanxingcun
          culture of 4000 to 3800 BC and the later Liangzhu culture,
          came from the Nanjing Museum in China; the fourth, discovered
          at a Liangzhu culture site at Zhejiang Yuhang Wujiabu in 1993,
          dates roughly to 2500 BC. 

          "What's most amazing about these mottled brown and grey stones
          is that they have been polished to a mirror-like luster," Lu
          says. "It had been assumed that quartz was used to grind the
          stones, but it struck me as unlikely that such a fine finish
          could be the product of polishing with quartz sand." 

          Lu's subsequent X-ray diffraction, electron microprobe
          analysis, and scanning electron microscopy of the four axes'
          composition gave more evidence that quartz could not have
          polished the stones: Fully 40 percent corundum, the
          second-hardest material on earth, the only material that could
          plausibly have been used to finish them so finely was diamond.
          
          To further test whether diamond might have been used to polish
          the axes, Lu subjected samples of the fourth axe, 4,500 years
          old and from the Liangzhu culture, to modern machine polishing
          with diamond, alumina, and a quartz-based silica abrasive.
          Using an atomic force microscope to examine the polished
          surfaces on a nanometer scale, he determined that the axe's
          original, exceptionally smooth surface most closely resembled
          -=96 although was still superior to -=96 modern polishing with
          diamond. 

          The use of diamond by Liangzhu craftsmen is geologically
          plausible, as diamond sources exist within 150 miles of where
          the burial axes studied by Lu were found. These ancient
          workers might have sorted diamonds from gravel using an
          age-old technique where wet diamond-bearing gravels are run
          over a greased surface such as a fatty animal hide; only the
          diamonds adhere to the grease. 

          The next known use of diamond occurred around 500 BC; it was
          used after 250 BC in ancient India to drill beads. The
          earliest authors to reference what is likely diamond, Manilius
          and Pliny the Elder, lived in Rome during the first century
          AD. 

          Lu's co-authors are Paul M. Chaikin of New York University;
          Nan Yao of Princeton University; Jenny F. So of the Chinese
          University of Hong Kong; George E. Harlow of the American
          Museum of Natural History; and Lu Jianfang and Wang Genfu of
          the Nanjing Museum. The work was supported primarily by
          Harvard University's Asia Center, with additional support from
          MRSEC grants and Princeton University's Department of Physics.
          
          Contact: Steve Bradt
          steve_bradt AT harvard.edu
          617-496-8070
          Harvard University

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