The use of a diamond splinter turned by a bow drill to drill the quartz beads in present day Cambay, India has been documented. A group of Cambay beads were made available for study. They were compared with a similar group of quartz beads excavated in Mantai, Sri-Lanka. These were dated stratigraphically c.700-1000 A.D. Silicone impressions were made of the drill holes from selected beads from both Cambay and Mantai. These were examined by means of scanning electron microscopy. The pattern of drilling was the same, suggesting that the technique of drilling with a diamond splinter and bow drill was an ancient one. This has not been previously reported.
Gwinnett, A. J. and Gorelick, L.
"Evidence for the use of a Diamond Drill for Bead Making in Sri-Lanka,"
Scanning Electron Microscopy: Vol. 1986
, Article 14.
Available at: https://digitalcommons.usu.edu/electron/vol1986/iss2/14