|
THE ART OF THE CUTTER
|
||
|
|
||
|
far
too great for an ordinary cement, no matter how hard, to be used to fix
the stone to the dop. So a solder or fusible alloy, composed of tin and
lead, is substituted. The dop containing the solder usually has an
external diameter of 1-1/2 inches, and a stout copper stalk is
fixed to the bottom of the dop. The dop is placed in a nonluminous gas
flame and heated until the solder softens, when it is removed by means
of the small tongs and placed upright on a stand. Long tongs are used
for shaping the solder into a cone, at the apex of which the diamond is
placed. The solder is worked well over the stone, so that only the part
to be polished is exposed. While still hot, the dop, with the stone in
position on the solder, is plunged into water in order to cool it. The
fact that diamonds withstand this drastic treatment testifies to their
thermal conductivity. Any other gem in the circumstances would split
into pieces.
The
dop is now ready to be attached to an arm or tongue; its copper stalk
is placed in the groove that runs across the split end of a screw,
worked by a nut. Four arms, each carrying a dop, can be used with one
polishing wheel.
The
copper stalk we were talking about is important. It is strong yet
flexible, and thus can be bent so as to place the diamond in the
position corresponding to the facet required to be polished. When the
workman receives the rounded stone he first must ascertain its point
and therefore the direction of the grain. Remember we already discussed
that technical thing "direction." After being sawn the stone is usually
four-point, the saw marks running parallel to one of the diagonals of a
square formed by the grain. Failing saw marks, a four-point stone
usually shows rough or slightly touched areas near the girdle, either
above or below, these being disposed at the comers of an imaginary
regular octagon. In a two-point mass the grain runs in one direction
across the table and there may be a distinct ridge.
(91)
|
||
|
|
||