Tube en Cuivre et phénomène du collier

Categorie Mégalithe 1
Categorie Mégalithe 2

Référence - Mégalithe




A Brief History of Drills and Drilling
6. Archaeological excavations have not yet produced copper or bronze drills in a lapidary context. We have been able, however, to provide evidence for the use of copper drills. through several serendipitous findings. The first occurred during an examination of quartz cylinder seals whose drill-hole impressions disclosed a peculiar anomaly on the sidewall (Fig. 10). We produced this same phenomenon, which we called a collar (Gorelick and Gwinnett 1989), quite accidentally while drilling on glass using a copper rod, quartz abrasive, and water (Fig. 11 ). We hypothesized that this occurred through plastic deformation of the copper rod's leading edge as a result of frictional heat and downward pressure on the rod. The ancient craftsman created the collars unwittingly during the course of drilling. If he added loose abrasive and lubricant in inadequate quantity, the drilling advanced slowly. A ware of this, ·he may have consequently applied greater pressure on the palm rest, thus distorting the drill. As he continued to add abrasive, the flare on the drill disappeared, but not before it produced a characteristic groove in the sidewall of the drill hole (Fig. 10). This phenomenon is unique to copper and the presence of a collar in the perforation of a bead is evidence of the use of a copper drill.

7. While bronze, a mixture of copper and tin, was used by craftsmen, it is speculated that it was rarely used in early metal-drill technology. The cost and scarcity of tin (Moorey 1982) would probably have precluded its use. Our unpublished experimental studies on drilling efficiency show no significant advantage of bronze over copper.