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304 GEMS AND PRECIOUS STONES IN THE
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touch
or softness of feeling which artists attained by the use of the
bow-drill. The instrument known as the dental drill is really an
improved form of bow-drill, working much more rapidly. An S. S. White
dental engine, provided with a suitable series of drill-points, answers
every purpose, and has been found especially useful in exposing fossils
and minerals when covered with
rock,
the objects being opened with great rapidity, with little danger of
injury. As shown by the author in a paper on a new method of engraving
cameos and intaglios,' an artist could be so trained to the use of this
improved bow-drill as to attain the same softness and feeling developed
by the old lapidarian masters.
In
the ancient specimens of work, tubes from which a core had been drilled
out by means of a reed and sand, revolved by the hand (see Fig. 18),
were done as neatly as anything can be done, the reason being that the
object was entirely drilled from end to end. This method of
drilling is still practised, except that the hollow reed is replaced by
the diamond or steel drill. When a valuable stone is being drilled, a
sheet of steel or a thin iron tube is substituted for it. The polishing
and grinding now is done on rapidly revolving disks, horizontal or lay
wheels, as they are called, whereas, formerly, the slow process of
rubbing with the hand on board or leather was perhaps resorted to. No
lapidary can do finer work than that shown by the obsidian objects from
Mexico (see Illustration), the labrets, and the ear-ornaments, which
are even more highly polished, though no portion of the circle is
thicker than 1/32 of an inch. An obsidian coyote head in the Blake
Collection in
1 Trans. N. Y. Acad. Sci., Vol. 3, p. 105, June, 1884, also Jeweler's Circular, June, 1884.
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