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Crystallus, Rock-crystal

Crystallus, Rock-crystal Page of 384 Crystallus, Rock-crystal Text size:minus plus Restore normal size   Mail page  Print this page
114                   NATURAL HISTORY OF GEMS.
kind; or where, the operation being reversed, the paste surface is backed by a facetted Crystal which serves to supply the required lustre. The ancient frauds in the matter of coloured gems went no farther than the above-named staining of the Crystal, and the substitution of pastes for the true stones. To detect the latter trick, Pliny lays down (76) many rules, some fanciful enough, but amongst them one infallible test, that a splinter of Obsidian will scratch a paste but not a real gem.
Fittingly to conclude the subject of False Gems, which naturally falls under the head of Crystal, so much em­ployed, either in its natural form, or chemically meta­morphosed, in their composition, we may insert some of the curious observations of Camillo, made before 1502, as to the various forgeries practised by the Italian jewellers of his own times. Many of these are extremely ingenious, and doubtless the recipes had been preserved in the tra­ditions of the craft from the date of the Empire. Besides making pastes of smalio (enamel) exact counterfeits of the true gems, they converted the commoner stones into others of the most precious kinds, by such illusive processes as that of cutting a Garnet very thin and backing it with Crystal to pass for a Euby ; an Amethyst hollowed out and filled with a coloured tincture imitated the Balais, which was also counterfeited by a thin table of the former laid upon a ruby-foil. Diamonds they forged by cutting the Beryl or the \Vhite Sapphire to the proper shape (a pyramid), and backing them with the customary tincture. To explain the latter term, it must be borne in mind that formerly the Diamond was always coloured black upon the culasse, with a certain composition, on the proper nature of which Cellini treats at great length in his ' Orefeceria,' as being of vital importance to the effect of the gem. In order to escape the test of the file, which no paste can
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