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Ostracias, Marcasite

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OSTRACIAS,
249
pharmacopoeia as caustics. Of these the most ponderous, the "Placitis," was divided into the "Onychitis," "ex­ternally azure, but spotted like the Onyx inside ; " and the " Ostracias," " entirely black," and the most powerful of all. It may therefore have been an agent in gem-engraving, like vitriol at present.
Cadmia (or Cadmea) is supposed to mean also Calamine-stone, from which one may suspect that the Ostracias of the Greek gem-engravers was the Marcasite, or Iron Pyrites, which, fractured, much resembles Calamine-stone ; when roasted, turns to a rusty led (testacea), and which has been used from time immemorial in Persia for polish­ing the harder gems. This last is indeed the strongest of my reasons for their identification. Ben Mansur states, "the Laal (Spinel) takes a polish with difficulty, and for a long time they were unable to polish it, until at last they brought it about by means of the Gold Marcasite called Ebrendsche." De Laet, in 1647, states that the Spinel and Balais could only be polished by means of the Pyrites. Modem lapidaries use vitriol for the same purpose, the principle of both processes being identical, vitriol being merely the extract of the Iron Pyrites.
It is indubitable that the Greeks derived all their pro­cesses of the Glyptic art from Persia, whence by the way of the Ionian cities the use of intagli had been introduced amongst them ; and whence, from Sardis in particular, most of the gems they possessed were exported.
But the use of Pyrites amongst the Romans in this art is not a mere matter of conjecture. Heraclius, in his all but unintelligible doggrel, ' De Artibus Romanoram,' written in the 7th century, actually speaks of engraving upon glass with " the hard stone known by the name of Pyrites."
Nevertheless my conjecture that actual copper-slag was
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