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Vitrum Annulare, Pastes

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368
VITRUM ANNULARE.
is pressed out into a vessel, and in it let the glass be placed for one night, together with the steel tool by which it must be en­graved. But when it is required to be used, let it be warmed again to the same degree of heat it had when it was first milked, and let the glass be always heated in it : and so it may be cut. In the same manner may other stones " ——
His directions for cutting crystal are so obscure that it will be more advisable to give them in the original than to attempt a translation, at the risk of substituting my own ideas for his :—
The sense seems this : to strengthen a plate of lead with two parallel bars of iron, which serve as a guide to the hand in rubbing the crystal; and to give the lead a cutting surface, sprinkle it with powdered potsherds,4 which get fixed in it by the pressure of the crystal upon them, just as in making watch-jewels at present the coarse diamond-powder, the Bort, is fixed upon the surface of a leaden disk by a few blows of a hammer before it is set agoing.
PASTE GEMS.
Although the Roman imitations of the precious stones—in two at least, the Emerald and the Lapis-lazuli—were truly admirable,
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