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378 THE MAGIC OF JEWELS AND CHARMS
illustrated
with a colored plate. The effect was that of a spectrum rather than the
iris effect of the crystalline quartz. This iris was also highly
valued, and great favor was set upon brilliant examples of what was in
reality rock-crystal fractured, the small fracture-planes causing the
breaking up of the light and producing the rainbow or iris effect. In
fact it was a spectrum produced by the mixture of quartz between the
chalcedonic layers.
Cellini
has a marvellous story to tell of a luminous carbuncle. A certain
Jacopo Cola, a vine-grower, going into his vineyard one night noticed
what appeared to be a bit of glowing coal at the foot of one of the
vines, but on reaching the spot he was unable to locate the source of
this radiance. Very wisely he retraced his steps to the spot whence he
had first observed the light, which became agaiît apparent, and when he
now very carefully approached the vine he found that the gleam
proceeded from a rough little stone, which he joyfully picked up and
carried off with him. He showed it to a number of his friends and among
them chanced to be a Venetian envoy, an expert on precious stones, who
immediately recognized that the find was a carbuncle. Thereupon taking
a base advantage of the finder's ignorance, he succeeded in buying the
stone for only ten scudi, and then hastened away from Rome, lest his
deception should be discovered. Not long afterwards this same Venetian
went to Constantinople and sold the stone to the Sultan of the time for
100,000 scudi, a profit of 10,000 per cent.2 The fact that
the vintner could only see the gleam from a given spot is in itself
sufficient proof that what he noted was merely the reflection of some
distant light striking a smooth surface of the stone at a certain angle.
Among the many virtues credited to carnelian by the
* Benvenuto Cellini, " Due trattati, uno intorno alle otto principali arti dell' oreficeria," etc., Fiorenzi, Valenti Panizzi & Marco Peri, 1568, fol. 10.
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