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NATURAL HISTORY OF GEMS.
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coating
over the coloured body of the vase ; and by cutting this away where
required, the design stood out in relief, usually upon a dark-blue
ground. The process, as the marks of the graver show, was precisely
that employed in cutting camei in hard stones. Fragments of large
vessels thus adorned are frequently met with amongst ancient ruins. Of
the perfect the Portland Vase is the most famous specimen ; and next to
this the Neapolitan, covered with an elegant arabesque of interlaced
vine-branches (Vitedm, p. 332). These ambitious attempts are aptly termed by Martial, " audacis pleboia toreumata vitri,"—tormina being
the technical name for ornamentation in relief, especially when
executed upon the surface of vases, whether in metal or in stone.
Another epigram (xiv. 115) informs us that the seat of this manufacture
was Alexandria, and that the risk of breakage during the operation was
very great, as might well be concluded from the fragility of the
material : —
" Aspicis ingenium Nili quibus addere plura
Dura cupit, ah ! quoties perdidit auctor opus."
Yet
the greatest artists of the day did not disdain to exercise their taste
upon so valueless a medium, for the relievi on the vases above
mentioned are far superior both in design and execution to any
decorating the celebrated vases carved in the real Onyx. This
application of the Glyptic art appears to be referable to Nero's times,
as may be deduced from Pliny's observation (xxxvi. 66), that a peculiar
mode of working glass (arte vitri) had then been discovered which made
two small cups of the kind called pterotae, or two-handled,
sell for 6000 sesterces (60Z.). So large a price could only have been
commanded by their artistic excellence, and not for any novelty in the
colour or body of the material; for it is mentioned in the same
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