inclinations and also to maintain exact parallelism between table, girdle and culet.
The
lapping and brillianteering are done by holding the properly mounted
stone against a rapidly revolving horizontal wheel of cast iron or
skeif . Diamond dust mixed with oil is fed on the wheel, which rotates
at the rate of 2,000 to 3,000 revolutions per minute. The dust has to
be carefully prepared from the diamond powder and bits obtained from
other operations and from fragments of poorer diamonds or bort. Four
stones could be polished at a time on a skeif.
It
has been found that there are variations in hardness in different
directions and faces parallel to crystal axes; cubic faces have two
optimum polishing directions, and facets parallel to these faces are
the easiest to polish. Dodecahedral faces are parallel to one crystal
axis, and each face has only one optimum direction. Octahedral faces
are equally inclined to three axes and are most difficult to polish.
But facets are not all parallel to a crystalline axis. The nearer a
facet is to a crystallographic axis or face, the easier is it to
polish. The sense of direction is usually determined by trial. An
expert polisher recognizes these important features quickly and
accurately.
These
facets based on the long experience of the cutting industry are fully
in accord with results of the studies on the atomic structure of
diamonds by X-rays.
Diamonds
are cut so that the table is parallel to a cubic, octahedral or rhombic
dodecahedral face. The cutting industry refers to the planes as four,
three or two point stones respectively.
Dops.—The holders to which stones are fixed for polishing are known as dops, which are of two kinds: (1) Solder dops and (2) Mechanical dops.
Solder dops.—It
is a basin-like holder which is filled with an easily fusible alloy of
tin and lead. While it is hot and pliable, the solder is shaped into a
hemispherical
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