VITRUM ANNULARE.	363
	tained its reputation long down into the Middle Ages, producing such remarkable enamelled pieces as the Cup of Charlemagne,9 so long treasured up in the Madeleine, Châteaudun. It sounds oddly to a modern ear to find Pliny alleging, as a proof of the proficiency of the Sidonian workers, that they actually made mirrors in glass ; but in his time, and long after, speculum metal, a particular alloy of bronze, was considered the only fit material for the purpose ; and even in the 15th century the Italians pre­ferred mirrors in polished steel, an example of which exists in the famous one of Lucrezia Borgia in the Soulages Collection. One Sidonian artist at least has contrived to perpetuate his name, for many handles of vases are known stamped Antas. Sidon., and the same repeated in Greek. In the old method they employed, besides the sand of the Belus, "white pebbles" (quartz) pounded, with a proportion of copper, and melted the mixture witb a fire of dry resinous wood.1 But later they had learnt to whiten their glass with the mineral magnes, evidently our manganese, " magnesia vitriariorum." The first melting was called ammonitrum, from its ingredients—sand and one-third of natron : this was melted again and purified before being worked into vases. The substance was elaborated in a variety of ways, " some being fashioned by blowing, some polished on the lathe, others engraved after the manner of silver-plate." Glass,-remarks Pliny, had superseded gold in the form of drinking-vessels at the tables of the great ; but the gain in point of economy was but little, since these were manufactured with such elegance that Nero gave six sestertia (60Z.) for a pair of small two-handled vases (" pterotae"), doubtless belonging to the same class of artistic productions as the Portland and similar rarities already noticed.