Cutting Diamonds and Other Gems 205
The
process of cutting gems is simple, but the results are due to the skill
and especially to the judgment of the cutter. That part of the surface
of a rough stone at which it is desired to place a facet is rubbed with
a harder stone or with some other effective substance. The harder stone
or substance abrades small fragments and powder from the softer, and
gradually the surface of the subject mineral is transformed into a
plane face, or facet. In like manner other facets are added or a
rounded surface is produced by similar means. In grinding, the harder
stone or abrasive material is reduced to a fine powder and mixed with
olive oil into a paste (if diamond powder), or with water (if emery),
and placed near the edge of a circular disk, or " lap," which is about
twelve inches in diameter and an inch in thickness. The lap, usually
of metal, revolves horizontally with great velocity, and the precious
stone to be ground is pressed against the disk where the disk is loaded
with the abrasive paste; the pressure causes the powder to become
embedded in the soft metal of the disk. This acts as a file, equal in
hardness to the grinding powder. The duration of the operation depends
upon the hardness of the precious stone and of
