206 A Book of Precious Stones
the
abrasive material. The skill required of the operator involves the most
careful watchfulness against exceeding the size prescribed in the plan
for the stone; also against overheating the stone, which causes the
development of small cracks in the interior of the stone called " icy
flakes." An essential prerequisite for grinding precious stones is a
means by which they can be held steadily and true in a desired
position. For this the diamond-polisher uses a time-honoured tool
called a " dop" (commonly pronounced "dub"). This holder of the rough
diamond is a small hemispherical cup of iron attached by the convex
side to a stout copper rod. The cup is filled with an easily fusible
alloy of tin and lead, which is fused and allowed to cool; just before
this composition solidifies the stone to be cut is set in the position
desired in the coolÂing alloy, with about half its bulk projecting from
the metal. Thus the stone is firmly fixed in an immovable position. The
semi-precious stones, when cut by the lapidary, are set in the end of a
wooden holder, or " stick," with some kind of resinous cement.
Diamond
cutters formerly cut the diamonds in a small wooden box especially
designed for this use; all of the operator's strength was
