There
are two modes of mounting precious stones—one, which leaves only the
upper part visible, called the close-setting; and the other, leaving
the stone uncovered both above and below, called the open-setting.
A
modification of the open-setting, called the knife-edge setting,
leaving the edge of the stone clear, is used with beautiful effect for
diamonds.
ENGRAVING OF PRECIOUS STONES.
When
we examine the marvellous artistic productions, executed in cameo or
intaglio, upon precious stones, we naturally think that the means
employed must be numerous and complicated, but in reality the apparatus
and the tools of the engraver are as simple as those of the lapidary.
They consist of the lathe, and a series of little rods with heads of different shapes, all of which can be adjusted to the lathe.
The
lathe, as will be seen from the appended figure, is a very simple
affair. The axis, driven by the belt from the wheel, is pierced at the
centre with an orifice, into which the tools for cutting the stone are
firmly fixed by means of a screw. The engraver wets the extremity of
the mounted rod with diamond-dust made into a paste with olive-oil, and
as the wheel is in motion he applies the
