<HTML>Stephen Tonkin wrote:
<snip>
>Archae, I am asking this from a position of profound
>ignorance, but is it possible that the spiral striations
>could result from rotation of the drill as it was withdrawn?
>It is common practice to keep rotating a drill whilst
>withdrawing it as it reduces the chance of it binding
>(probably a 'sticktion' vs 'friction' issue).
>Probably a non-starter, but I thought I'd ask...
It is possible I suppose, however the sides of the core and/or core-hole are both tapered in most of these examples making binding of the coring bit less likely. However, the sides of both are parallel in the drilling of the central core hole of stone vases, used for the purposes of hollowing, the AE are obviously using a different technique in these examples (Stocks 1993, demonstrates how this can be done) than that of the granite core #7. I should look up and see if there are any descriptions of striations on these vase cores and see if they are different, since there is no wobbling of the coring-bit. As well, a lapidary drill of the AE type would have a tendency to fill to some degree with tailings as the cutting is done with dry abrasive (as Stocks (2001) suggests), this might produce a binding problem, although if slurries are used they could be washed out.
Stocks (2001) states that a force of about 1 kg/cm^2 on the cuting surface of the bit is needed to cut granite with dry sand abrasive and horizontal striations are noted in these experiments... this suggests that some force is needed on the cutting points of the quartz abrasive grains to produce striations. I suspect that the force generated during the removal of the coring bit from the drill hole would not supply sufficient stress to produce the characteristics of the striations noted by others.
Stocks, D.A. (1993) Making Stone vessels in Ancient Mesopotamia and Egypt. Antiquity, 67, 596-603.
Stocks, D.A. (2001) Testing Ancient Egyptian Granite-Working Methods in Aswan. Upper Egypt, Antiquity, 75, 89-94.
Archae Solenhofen (solenhofen@hotmail.com)</HTML>