USE-WEAR ANALYSIS OF DRILL BITS

The particular question in this case was whether or not some form of mechanical drilling was involved in the manufacture of carnelian beads.

The specialized nature of this study presented some technical problems.

The evidence of use wear present on the tips and/or sides of the drill bits meant that a magnification of 200 times was often inappropriate for looking directly on to the tips of the drill bits. The depth of field at 200 magnifications meant that the area was too small to observe the use wear. A 100 magnifications was often more appropriate for observing the polish.

For looking at the amount of rounding on the tips of the drill bits a magnification of 50 times was often used in order to be able to observe morphological changes to the drill bits that was caused by use.

Observation was concentrated on the use wear features of rounding, presence of polish and circular striation patterns, together with the fractures at the tip caused by rotation (torsion fractures) or by percussion (flute and burin like fractures).

Other morphological features such as edge angle, profile, shape etc. are not discriminatory as this class of tool are almost uniform morphologically within very narrow parameters

Another major difference in this study was that not only the tools were examined but also the worked material in the form of partially manufactured or broken beads. This meant that correlations could be made between the wear traces on the tools and the wear traces produced by the tools.

It has been demonstrated that carnelian beads can be perforated by a punch technique that does not involve drilling at all. Chevalier, Inizan and Tixier 1982.

So the experimental program included attempts to replicate this punch technique as well as using a mechanical drilling action.

All of the experimental drill bits exhibited the rounding, polish and circular striation pattern.

tip of experimental drill bit 100x magnification

Often the rounding would form and then break away leaving small areas of polish with striations on the sides of the drill bits, most of the tip having been lost.

This was also observed on the archaeological drill bits

tip of archaeological drill bit 100x magnification

The rounding and circular striations were also observed when looking at the side of the tip of the drill bits.

side of archaeological drill bit 100x magnification

Further evidence of the use of a mechanical drill was provided by the microscopic examination of the carnelian bead blanks. The surface adjacent to the hole has circular striation.

carnelian bead 100x magnification

These observations of the drill bits and the carnelian bead blanks, allows for the reconstruction of the technique used in perforating the beads. After the blanks were prepared pecking would have been used to provide a slight indentation in the center of the blank,

(the majority of the blanks broke at this stage i.e. when a percussive action was being used). The indentation would then allow the drill to be placed in position at the center of the blank without skidding away across the surface.

Drilling would then be used to perforate approximately half way through the blank.

The completion of the perforation seems to have been achieved by the removal of a conical flake

That is a drill bit is placed in the hole and struck, producing a conical fracture scar, and this completes the perforation.

All to the beads observed from Larsa had perforations whose outlines were irregular as with the pecked perforations of the Kumartepe beads.

None had circular perforations with concentric striations demonstrating that at Larsa a drilling technique was not used, but the punch technique was used throughout to manufacture the beads. That is the perforation through half of the bead blank and the final blow to detach the conical flake was all achieved by pecking; as opposed to the initial drilling and then final perforation by punch technique as seen at Kumartepe.

The kind of drill envisaged is a bow drill or a pump drill

The drill bits from Kumartepe are small and made of bladelets produced by burin technique.

It is interesting to note that two different techniques were used to achieve the same end with the same material.

The other main difference between the sites is that of quantity, there being thousands of drill bits at Kumartepe while only 52 tamponnoir , or punches, have been recovered from Larsa.

The difference in quantity of material and manufacturing techniques suggest an interpretation of Kumartepe as a factory site as opposed to Larsa's cottage industry.

Calley, S. and Grace, R.1988.
Drill bits from Kumartepe, Turkey. In In Beyries, S (ed). Industries lithique: tracéologie et technologie. B.A.R. International Series 411 (1)pp 69-82.

Chevalier, J., Inizan, M-L. and Tixier, J. 1982.
Une technique de perforation par percussion de perles en cornalin (Larsa, Iraq). Paleorient 8(2);55-65.

also see:-
Grace 1989 chap. 5