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Vitrum Annulare, Pastes

Vitrum Annulare, Pastes Page of 384 Vitrum Annulare, Pastes Text size:minus plus Restore normal size   Mail page  Print this page
350                 NATURAL HISTORY OF GEMS.
tained lier reputation long down into the Middle Ages, producing such remarkable enamelled pieces as the Cup of Charlemagne,* 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 that said to be Lucrezia Borgia's in the Soulages Collection. One Sidonian artist at least has contrived to perpetuate his name, for many handles of vases are known stamped with Aetas. Sidon., and the same repeated in Greek characters. 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 with a fire of dry resinous wood, j 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
* In reality made towards the end of the twelfth century, as the fine inscription covering its surface announces. The same city was the source of the Venetian manufacture : the earliest glasses of that fabrique which go back as far as 1490, are gilt and enamelled in precisely the same style. (Seo J. C. Robinson's ' Memoir on Venetian Glass ' in the Soulages Collection.)
t " Continuis fornacibus sicut sera," in a succession of furnaces like copper, without being allowed to cool ; or it may be in a revorberatory furnace like that now used in copper-smelting; for in his notice of cadmea he mentions the camara as well as the latera of the furnace, showing that it was arched over.
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