My thoughts are - have you found any stones with blobs of melted copper slag on ? (I'll bet you haven't). Would the attached bits of metal - which must have suffered badly by four thousand years of erosion - be considered Rock Art, if they could be shown to be genuine ? It fits in with that spear mould (in how many pieces?) that's in Tullie House. Such speculation is much more interesting than going to exhibitions (unless it's Rembrandt prints, of course).