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NATURAL HISTORY OF GEMS.
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wheels
of various diameters, worked as the others, and supplied with
diamond-dust and water. The Carnelian beads are finished by putting a
number into a bag in which they are shaken together."—(' A Visit,
December. 1832, to the Carnelian Mines, situated in the I'ajpeepta
Hills, to the eastward of Broach. By Lieutenant G. Fulljames.')
Both
the Onyx and the Sardonyx are now largely imitated by artificially
preparing the German species, a stratified quartz, in quality little
superior to common flint, by which treatment factitious stones are
produced of much beauty, exhibiting well defined and even layers of
black and white, or red and white, equally clear and vivid.* This is
effected by boiling the stones continuously, for the space of three
weeks, in a solution of honey in water, constantly replenished as it
evaporates, and afterwards steeping them in sulphuric acid to bring out
the black and white ; in nitric for the red and white colours.f The
more porous strata absorb the honey first, and, secondly, the acid that
carbonizes it—the more compact remaining unaffected by either. Such
imitative gems are of very trifling value, being imported in vast
quantities from Germany, where the secret was either discovered some
years ago, or else, as others assert, introduced from Italy, where it
had been practised from time immemorial. Pliny himself notes that all gems are
brightened up by boiling in honey (mellis decoctu nitescunt),
especially in the Corsican, noted for its acridity, although all other
acids are detrimental to them (xxxvii. 74). There
*
The true antique Sardonyx lias a peculiarity that serves, in addition
to the superior beauty of its colours, to distinguish it infallibly
from these German counterfeits. Its black substratum when viewed by
transmitted light, turns to a rich chocolate-red highly translucent,
whereas the same part of the artificially stained recent species
continues as black and opaque as before.
t Another sort display shades of a beautiful sapphirine produced by a similar application of the prussiate of potash.
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