Furnace linings, tuyeres, and crucibles dating from the third millennium BC to the Medieval period have been examined using thin-section microscopy and scanning electron microscopy with energy dispersive x-ray analysis, and subjected to refiring tests. Smelting furnace refractories are comparable in composition to modern brick clays; locally available materials were selected and exploited with only minimal treatments such as tempering. Crucibles in the Roman and Medieval periods were made from relatively refractory clays, but the same clays were also used to make domestic pottery in these periods. The craftsmen appear to have restricted their use of refractories to materials that were easily accessible; the requirements of the metallurgical processes were such that the exploitation and development of exotic materials was unnecessary. -- AATA