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Besides pastes of Sraalto, which exactly counterfeited the true gems, they converted common stones into others of a more precious quality by various curious processes. Thus a Garnet cut very thin and backed with Crystal, was sold as a Ruby; an Amethyst hollowed out and filled with a coloured tincture imitated the Balais, which gem was likewise counterfeited by a thin tablet of Amethyst laid upon a ruby-coloured foil. Diamonds were forged by cutting a pale Sapphire or a Beryl to the right shape, and then backing it with the proper tincture. To understand this, it must be observed, that until quite lately Diamonds were always set upon a black ground, to give them lustre: on the proper preparation of which Cellini treats at great length in his 'Oreficeria,' as being of the utmost importance to the effect of the stone. To baffle the test of the file, which no paste can resist, the forgers of the time of Camillo Leonardo chiefly imitated the Emerald aud the Peridot, as these gems are in reality but little harder than glass, and yield to the file almost as easily as their counterfeits in paste; so that the sole means of detection remaining, was to examine them by the light of a candle, when the colour of the false, gems would be found to fade away the more intently they were viewed.
The annexed epigram is entitled in the Anthology, " Upon an Engraved Crystal," in which case it would give us the name of another ancient engraver of the Greek period; but the expressions of the epigram itself would rather make me conclude that the portrait was painted in gold on the back of a piece of glass, which was covered by another piece fused upon it, so that the painting appeared enclosed in the substance of the glass, of which art some beautiful specimens arc still preserved.9
» The finest prouubly of these is perty of Dr. Conyors MiJdleton, ami the portrait of a child, once the pro- now in the British Museum.
DiODORtrs, Anthol. ix. 776.
"The art and colour well might Zeuxis claim,
Renaissance Crystal intagli are sometimes found in jewellery of that period, set with the engraved side downwards upon a gold or azure foil. The effect thus produced is very singular, the figures appearing as though cut in relief in a transparent gem, a Topaz or Sapphire, and the deception is so perfect as only to be detected by the touch. A veiled bust of the Madonna, thus treated and set in a ring, the first instance of this ingenious device that came under my notice, puzzled me for some time, by the apparent relief of the work upon an actually plain surface. This style of work in Crystal is also mentioned by Mariette, in whose time several had been circulated amongst the Parisian connoisseurs as antiques of the Roman period.
The Romans used to give fabulous prices for vessels in this material. Pliny mentions a lady, and one too by no means wealthy, who bought a Crystal trulla for a sum equal to 1500Z. of our money; and Nero, to avenge himself upon the world, when informed of his deposition by the Senate, threw down and smashed two crystal bowls, scyphi, engraved with subjects from Homer.
Crystal is found in very large masses; the largest known to the Romans weighed 50 pounds, and was dedicated by Livia in the Capitol; and a bowl is mentioned which held fonr sextarii, or about two quarts. I myself have seen a rolled Crystal more than a foot in length, of a perfect egg-shape, and of admirable transparency. It had formed a part of the plunder of Delhi, and was intended to be cut into a vase, the capacity of which would doubtless approach to that recorded by Pliny.
The balls of Crystal occasionally found amongst ancient remains were used as burning-glasses.10 That they were thus employed by surgeons appears from the passage of Tliny: "I find it asserted by physicians, that when any part of the body requires to be cauterized, it cannot be better done than by means of a crystal-ball held up against the sun's rays." Orpheus (170) recommends their employment to kindle the sacrificial fire:
"Take in thy pious hand the Crystal bright,
The Cairngorum, so much in fashion at the beginning of this century, that Mawe (1804) speaks of ten guineas being the usual price of a seal-stone, is only a Crystal coloured a
10 They were also hold in the hand ncss during the fiery heat of the for the sake of their refreshing cool- southern summers.
dark orange or deep brown by some metallic oxide. Some of them are certainly very beautiful, much resembling the Jacinth, and are by far superior in lustre to the German Topaz, a stone of the same kind, and now imported in such large quantities.
Crystals and Agates are not uncommon in collections, containing a small quantity of water in a cavity left within them at the time of their formation. I am informed that iu California the miners often meet with large nodules of quartz thus filled, and are often killed by drinking the liquid contained therein, so strongly impregnated is it with silica. This is the Enhydros of Pliny and the Medieval mineralogists, who looked upon it as a most wonderful miracle of nature, to judge from the numerous epigrams, of which it has been thought worthy by Claudian and other poets:—
Epigram VIII. et seq.
"When the Alpine ice, frost-hardened into stono,
Mark where extended a translucent vein
A stream unfettered pent in crystal round,
Erst, while the boy, pleased with its polish clear,
Streams which a stream in kindred prison chain,
Hercules Mad: Etruscan. CryataJ.
I have read of one of these pregnant crystals exploding when held in a person's mouth, in consequence of the expansion of the inclosed fluid, and lacerating his palate very dangerously, Whether the water was inclosed within the stone at the time of its formation, as the ancients supposed, or afterwards infiltrated through its pores in the lapse of ages, is still a matter of dispute. I have myself seen the hollow spherical portions of the stems of Venice glasses nearly filled with water, which has penetrated either through their sub