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@harvard.edu
617-496-8070
Harvard University