experimental archaeologists (forget the names, sorry) drilling egyptian granite with egyptian sand† found that copper tube drills work better than bronze tube drills, presumably because copper is, as the machinists say, 'gummier'
so while you're right that copper is much less useful than bronze for most tools, here the tool we're talking about is one of the exceptions
they also tried tubular reeds, with and without water. those didn't work at all
the egyptian state seems to predate not just tin bronze or even arsenical bronze but even copper tools, at least in egypt
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† emery doesn't occur locally and doesn't start appearing in the drilled holes during the first millennium of rock drilling
While you are right about pure copper being the best for such drilling with free abrasive, a few niche use cases for pure copper do not make a "bronze age" into a "copper age".
Even after the much cheaper iron replaced bronze for most uses, bronze remained the best choice for a few purposes, but nonetheless that does not override the transition from the bronze age to the iron age.
While emery does not occur locally, the island of Naxos is closer to Egypt than many other places from which various goods were imported at that time, so that was not a serious obstacle against its use.
The conclusion of the parent article was that emery (with copper cylinders) produced the best matches with the archaeological artifacts, so that was the most probable method used for drilling (the other possible alternatives, like importing diamond dust or corundum dust from India have probabilities far too low to be believable; what we name now as diamonds became known to the Mediterranean world only after the expedition in India of Alexander the Great; the word "diamond" is much older, but it was previously applied to osmium-iridium alloy nuggets, which are found together with gold nuggets in alluvial deposits and which are embedded in the gold of many ancient Egyptian artifacts).
i agree with almost all of your comment. just a few minor points:
- there was a 'chalcolithic' period of copper tools in most places before the advent of bronze, but i believe that bronze tools were already in use in egypt when drilling started
- later investigations did not find emery dust in the oldest drill holes, leading to the conclusion that the abrasive was quartz, so although the egyptians certainly could have been importing abrasives from naxos, they don't seem to have done so until much later
- the identification of plato's 'adamas' with an osmium-iridium alloy is quite dubious; he was certainly talking about a metal, but it could easily have been steel or meteoric iron
- just to clarify, you probably know this, but corundum dust and emery are the same thing (the article was fairly confusing on this point)
so while you're right that copper is much less useful than bronze for most tools, here the tool we're talking about is one of the exceptions
they also tried tubular reeds, with and without water. those didn't work at all
the egyptian state seems to predate not just tin bronze or even arsenical bronze but even copper tools, at least in egypt
______
† emery doesn't occur locally and doesn't start appearing in the drilled holes during the first millennium of rock drilling