Ancient Chinese craftsmen might have learned to use diamonds to
grind and polish ceremonial stone burial axes as long as 6,000
years ago, according to a report published in the February issue of
the journal Archaeometry.
A team of researchers led by Peter J. Lu, a graduate student in
physics at Harvard University's Graduate School of Arts and
Sciences, uncovered strong evidence that the ancient Chinese used
diamonds with a level of skill difficult to achieve even with
modern polishing techniques.
"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," said Lu.
The finding places the earliest known use of diamonds worldwide
thousands of years earlier than was previously believed. Most
scientists believe the earliest use of diamonds was around 500
BC.
Lu's work also reveals the only known prehistoric use of
sapphires.
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.
Lu 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 was discovered at a Liangzhu site in Zhejiang
Province.
Using X-ray diffraction, electron microprobe analysis and
scanning electron microscopy to examine the polished surfaces, Lu
determined that the axes' original, mirror-smooth surfaces closely
resembled yet were superior to modern stones machine-polished with
diamond. Since corundum is the second-hardest mineral on earth, he
concluded that the surface could only have been achieved by using
diamonds as polishing agents.
Sources of diamonds exist within 250 kilometers of where the
burial axes were found.
Lu's work may eventually yield new insights into the origins of
ancient China's Neolithic artifacts, which include vast quantities
of finely polished jade objects.
"I imagine that Neolithic craftsmen were constantly
experimenting with new tools, materials and techniques," Lu
said.
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.
(China Daily February 18, 2005)
