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TREATMENT AND CARE OF PEARLS 379
with
a V-shaped groove on its edge, to admit of the string being passed
entirely around it like a pulley, so that when the drill is placed on
anything and held at the other side, and the bow is moved up and down,
the wheel with the drill end rotates rapidly.
If
the pearl is not properly secured, if the drill point is too irregular,
if it is not properly centered, or if it is too rapidly rotated at the
start, one or more layers of the pearl are likely to be broken, giving
an irregular, ragged appearance. If, again, the drill is rotated too
rapidly as it is leaving the other side of the pearl, one or more
layers are occasionally forced off, and this in turn will produce a
break on the pearl. It happens not infrequently that pearls are broken
away on the surfaces at both drill holes if the workman is careless.
As
pearls have become more valuable, only the most efficient workmen are
employed in drilling them. Whereas formerly a drill hole would be half
a millimeter in diameter, at present it is much smaller, and such
drilling requires the greatest skill in manipulation. The use of these
very fine drill holes is due principally to the fact that pearls have
become so valuable that the slightest loss, even the fraction of a
grain, would amount to a considerable sum in a necklace of large pearls.
When
a pearl has been perforated with a very fine drill hole, the hole may
be enlarged somewhat by using a slender copper wire, the fineness of
the drill hole itself, charged with either diamond-dust, emery, or
sand. When the wire thus charged is drawn in and out, the drill hole
can be enlarged to any desired size.
A
large pearl is held in the hand or secured in a wooden block, or else
it is held in a small pair of forceps with a rounded, cup-shaped
receptacle at the end, which is usually lined with chamois leather and
is pierced with a hole through the center. This hole serves as a guide
for the drill, directing it while the pearl is being perforated.
Adjustable cups or forceps with cup-like ends of every size are
necessary, according to the size of the pearl ; and in order that it
may be properly seen, it is requisite that the pearl should always be
larger than the cup in which it is placed.
The
poorest part or spot is selected to form the beginning of the drill
hole. The pearl is placed in a pair of calipers with a circular disk,
one end of the caliper being placed on the spot to be pierced, the
other end naturally touching exactly opposite, the pearl absolutely
centering it. As these caliper ends have been rubbed with either
rouge, lampblack, or some colored substance that will readily rub off,
these two spots of color remain on the pearl and serve as a guide for
the driller. The drill end is then placed on the pearl, and the bow
moved up and down ; and so rapid is this work that five pearls weighing
fifteen
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