grains
each can be drilled with the greatest care in less than one hour's
time. Of small pearls, weighing about one grain, as many as fifty have
been drilled in less than one hour by the hand-drill method.
Many
of the thinnest and best drills are made out of thin steel needles.
These are ground flat by means of a small carborundum wheel, so as to
have two flat sides. They are then thin pointed, and with a V-shaped
edge. These prevent the drill from clogging up, allowing the fine dust
to pass upward and outward readily, and the hard steel almost
invariably penetrates the central core of the pearl, no matter how hard
or tough this may be. The needle-drill is then secured in a small chuck
attached to the brass revolving wheel. Some recommend lubricating a
drill with milk when it is employed for piercing a pearl, but a
well-made drill, that allows the dust to escape as it is formed, does
not require this treatment. The drill should always be made to revolve
quite slowly so that no unnecessary heat may be generated by friction
to injure the color of the pearl and also to avoid the possibility of
the drill becoming clogged by the pearl-dust.
By
means of centering calipers or markers, the driller, especially in the
drilling of a large pearl, will generally drill first from one end, and
then reverse the pearl and drill from the other end, meeting
absolutely in the center. This prevents the breaking of the outer
layer of the pearl. A skilful workman can, by turning the pearl, so
operate the calipers that the true center can be obtained, even if the
pearl is not absolutely round, and the drill holes so centered that the
irregularity of the pearl is less apparent.
When
the pearl has been half drilled through from one side, considerable
caution is necessary in drilling from the other, that when the two
drill holes are about meeting the drill be not revolved too rapidly, as
the clogging is likely to crack the pearl or break the drill. If the
pearl is only to be drilled one fourth or one half through, the depth
can always be gaged by watching the drill-end, first, by measuring the
drill-end itself, and, secondly, by noting to what part of it
pearl-powder adheres.
Pearls
are more easily manipulated than any other gems. They are also more
easily damaged. Still, when properly treated by the workman, there is
no material that offers him more satisfactory results than the pearl,
if good judgment be used.
Drillers
occasionally find that when the drill reaches the center of the pearl,
there is a sharp click, the pearl often breaking at this point. This is
evidently due to the fact that a harder kernel may exist in the center,
such as a tiny grain of sand, which can turn the drill-point; or else
the resistance may cause the tiny drill to break.
