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ONYX.
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became
brown and transparent after having been worn a few hours upon the
finger, in consequence of the absorption of the perspiration from the
skin by its porous substance. Not being aware of the cause, he supposed
the gem to be a Hydrophane or Oculus Mundi, a kind of Opal that goes
through a similar change if saturated with water. Similarly another gem
of mine, a fine Sard, engraved with a head of Sapor II., filled with
white spots owing to a partial calcination, recovers its pristine pure
and crimson transparency after a few days' wear on the finger. These
experiments tend to verify Pliny's recipe for improving the lustre of
the Carthaginian Carbunculus (above quoted), by a fortnight's
maceration in vinegar.
Ben Mansur describes the Onyx (Dschesi) as divided into two species :—The Bahrawi of three layers : the first, opaque red ; the next white ; the third, transparent like crystal : and the Haheschi, also of three layers—two dark, and a white one between them (the actual ïíý÷ùí of
the Greeks). " Some are striped, othors are not : in others the stripes
are so interrupted that they form curious figures." * Interesting also
is his notice of the localities yielding it :— " Although the Onyx is
found in many places, yet those most valued are dug up on the confines
of India and of China." From which it appears that, like the early
Greeks, the Persian mineralogist makes no distinction between the Onyx
and the Sardonyx.
In
the same measure as the Alexandrian glass-workers counterfeited with
astonishing success the natural clouds and polished surface of the
Murrhina, so did they reproduce with equal skill, in their cheaper
material, the precious Onyx vases and the cameo designs embellishing
their surface. This was effected by fusing an opaque white
* On which account it faires with us the popular name of "Fortification-Agate."
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