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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
VITRUM ANNULARE.
325
as he was, gives many curious and valuable recipes. In the present day the trade is transferred to Paris ; and it will be seen by a reference to the article Strass, how important au ingredient in paste-making crystal is" still regarded. Crystal in fact being the purest form of silex, is very superior to the silicious sand now employed, for the sake of economy, in the manufacture. The use of this component can be traced back to the earliest times, for according to Pliny (xxxvi. 66), " some assert that in India glass is made out of pounded crystal, and in consequence no other sort is comparable to the Indian " (Crystallus). The same fact seems to be implied in the vague expressions of Theo-phrastus (49) : " For if glass be made, as is reported, out of the hyalites, this substance also is the product of condensa­tion." And Plato has (Tim. 61 c.) " some substances con­taining a smaller proportion of water than of earth in their composition as the entire species of glass, and whatever kinds of stones are termed fusible."
Besides this superior hardness, another supposed criterion of an antique paste is the beautiful iridescence, often coating its surface, produced by the oxidising of the glass from the action of the salts of the earth. Another is the porous, bubbly texture, not only of the surface, but of the entire body. The latter peculiarity does indeed distinguish them from those of the modern fabrique, which, when they counterfeit the transparent gems, are pure and homo­geneous throughout, being in fact made of what is techni­cally called " pot-metal," glass stained of one colour. Those, from the greater fusibility of the composition, usually exhibit a polished surface within the intaglio, not far below that of the real stone whence it was derived. But it must be remembered that an equal hardness would be found in modern pastes, only supposing them made out of the fragments of ancient glass (abundantly procurable
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