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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
358
NATURAL HISTORY OF GEMS.
Strass, so called from the German chemist who invented it, is the brilliant White Paste, the material of Paste Diamonds. It will be seen that, coloured by different metallic oxides, it reproduces the other gems. Barbot gives many varying recipes for its composition ; but they have, as far as the Diamond is concerned, been superseded by a quite recent discovery of the ingenious Parisian chemists. By a preparation of borax (as yet a secret) a paste, the " diamant de bore," is produced as hard as quartz, defying the file, and when set in real gold (as such now are) not to be distinguished by the most practised' eye from true brilliants.
ENAMELS.
Enamels, though the same in composition as pastes, differ in the mode of application. The vitreous mass is ground fine, and then, mixed with gum-water, is applied with a brush to the surface to be ornamented, upon which it is finally fixed by means of fusion. From the degree of heat necessary in the operation, the substratum must be either fine gold or pure copper, capable of resisting it, otherwise the slight compartments formed in the metal to contain the enamel would run, and the outlines of the pattern be deranged. The basis of all ancient enamels, for which Mediaeval writers give many recipes, is powdered glass or flint, oxide of lead, and borax, mixed in various proportions, arrd coloured by different metallic oxides. It was a Celtic invention, made to replace the Áéèïêüëëøá, or inlaid gem-work of the Orientals, by a cheap and attainable imitation in the baser materials of glass and copper. This we learn from a passage in that pretty piece of Philo-stratus, the Imagines, or ' Picture Gallery,' where he is describing the Boar-hunt (xxvii.) :—" The horses have their bits plated with gold, and their head-ornaments are
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