Evening star., 1935-03-24
SINGLE GEM CUTTER AND HIS

special pulley for operating the
wooden lap whose upper face, covered
with taut piece Of canvas, Is slightly
convex. This canvas holds the abra-
sive on the rapidly rotating surface.
This buffer Is particularly adapted for
polishing large surfaces Of petrified
wood, smoky quartz and similar speci-
mems.
In facet-cutting diamonds are cut
in this manner) such semi-precious
stones as rock crystal, smoky quartz,
citrine and amethyst are first roLghed
to the approximate size desired on
the coarse carborundum wheel. Then
the table, or top face of the stone,
is ground fat and smooth previous to
mounting it with sealing wax or
chaser's cement on the end and
exactly at right angles to the length
of q rounded stick The specimen is
mounted with its table fiat against the
squared end Of the stick. An ingenious
device used by Mr. Bumstead facili-
tates this squaring procedure. The
arrangement Is such that while the
sealing wax is still hot, the stick is
placed in the grooved channel of this
appliance and pressure is applied: the
stone Is seated with the table truly
squared with the axis of the stick.
Mr.. Bumstead next clamps the stick
to another apparatus which he has
contrived. which governs the position
of the stone during the grinding on
the horizontal wheels, or laps. The
device is made from the graduated
base of one of the sun compasseS
which Mr.. Bumstead originated, the
set-up being such that the stick can
be turned through different angles in
order to grind and polish successive
facets. The stone is now in position
to grind its base, or pavilion faces,
which give maximum brilliancv when
cut at an angle Of approximately IS
degrees from the plane Of the girdle,
the girdle being the largest circumfer-
ence of the stone. The above dimen-
sion holds true only if the gem is bein5
cut from some variety of quartz.
Mr.. BUMsTEAD uses an instrument
called a clinemometer in adjust
ing the slope Of the stick On the
graduated circle of this device on the
end of the stick holding the stone, the
angles are measured for turning from
one facet to the next. This crafts
mans work bench is equipped with
leveling device for making the grinder
truly horizontal. These detailed opera
tions are fundamental in facetting
and typifying the extreme precision
and accuracy essential for satisfactory
results.
In facet polishing. the lapidist has
to exercise extreme care not to scratch
the faces of the stone. Polishing Is
performed on a disk wheel or lap OF
tin with tin oxide and water used as
the polishing agent. The facets are
polished in exactly the same order
that they were cut The adjustments
of the holding device are made very
accurately during the polishing and
the stone is inspected frequently under
a magnifying lens to assure that the
polishing is carried far enough to re-
move all of the marks of grinding and
vet not so far as to injure the shape
of the adjoining faces. This finishes
the cutting and polishing of the pa
vilion facets.
! A smooth, solid tin wheel will
scratch the stone. To prevent such
a catastrophe, the wheel is scored
with long radial lines about one
| quarter inch apart cut with pocket
| knife or razor blade. The wheel is
then run fairly fast and its surface
is smoothed slightly by using 1t to
polish agateS with tin oxide anc
water. That treatment gets the tin
/ lap in desirable condition, so that 1t
will polish the facets without scratch
| ing or otherwise damaging them. One
| other precaution is to use a very
! thin mixture of the tin oxide and
water for all facet polishing after
| the wheel has been etched or scored
with steel and smoothed with agate.
/ Clear quartz, smoky quartz and anne
/ thyst can all be made to bloom in
| the pristine glory of brilliant colors.
Topaz is one stone which cannot be
polished in this manner, as 1t per-
sists in getting scratched. 1t can.
however. be polished satisfactorily If
ruby powder is used instead OF tin
oxide.
There is only one way of producing
diamonds of greater brilliancy. than
those resulting from the facet system
of cutting. That consists in making
synthetic diamonds. Certain colors
are produced in the synthetic dia-
mondS, which are more beautiful
than any ever seen in the natural
stones. However, there is distinct
limit to synthetic diamond produc-
ton. as such simulations can now
be produced only in microscopic sizes.
Science gives little hope that syn
thetic diamonds will be produced
potentially in such size and on such
scale as to compete with the true
iamonds-valuable gems imported
chiefly from South Africa. Most gem
cutting by professional lapidaries is
done abroad, as the foreign specialists
work. so cheaply that American
lapidists are unable to compete with
them.
CII. C.L Cwo.e