, for diamond cannot be polished against the grain, nor even
exactly with it, but only obliquely across it. This requirement, as much
as anything, has prevented the use of machines in polishing diamonds.
The table is usually first polished on, then the four top slopes,
dividing the top surface into quarters, then each of the four ridges
thus left, is flattened, making eight facets and finally 32 facets,
exclusive of the table, are made upon the top of the brilliant. The
stone is then reversed and 24 facets, and the culet, polished on the
back. As each facet nears its proper shape the stone is placed upon a
particularly smooth part of the lap and a slight vibratory motion given
to the holder by the hand. This smooths out any lines or grooves that
may have formed because of inequalities of surface of the lap. When
completely facetted the brilliant is finished and requires only to be
cleaned, when it is ready for sale.

LESSON XXIII

HOW ROUGH PRECIOUS STONES ARE CUT AND WHAT CONSTITUTES GOOD
"MAKE"--_Concluded_

SLITTING AND CLEAVING. The cutting and polishing of precious stones
other than diamond is a trade entirely distinct from diamond cutting.
The precious stone lapidary cuts every species of stone except diamond.
The methods used by different lapidaries vary somewhat in their details,
and there are many trade secrets which are more or less jealously
guarded by their possessors, but in general the methods used to reduce
the rough materials to the finished gems are as follows: First, the
rough material, if of too large size, or if very imperfect, is
_slitted_, or, if it possesses a pronounced cleavage, it may be
_cleaved_, in order to reduce the size or to remove imperfect parts.
_Slitting_ is accomplished by means of a circular disc of thin metal
which is hammered so that it will be flat and rotate truly, and is then
clamped between face plates, much as an emery wheel is held. The smooth
edge of the circular disc is then charged with diamond dust and oil, the
diamond dust being bedded into the edge of the metal disc by the
pressure of some hard, fine-grained material, such as chalcedony, or
rolled into the metal by the use of a rotating roller. Once charged, and
kept freely supplied with oil, a slitting wheel will slice a
considerable number of pieces of any precious stone less hard than
diamond, and will do so with considerable rapidity. The wheel is, of
course, rotated very rapidly for this purpose.

Th