Gemcutting
The term gemcutting is a misnomer, although
the term is widely used to describe the
process of shaping and polishing faceted
gemstones, but certainly it sounds better
than rock grinder.
While the gemstone in the rough state may
be trimmed to remove undesirable material
or to separate it on a cleavage line with
a diamond bladed saw,
accurately described as cutting and once
done by the use of a chisel or similar tool
to simply break off pieces that were usable
as single gemstones just in case you remember
the old Lincoln commercials.
The actual shaping and polishing of a gemstone
is a grinding or sanding process.
This grinding and sanding is done using
a lap, a precision metal plate imbedded
with grit similar to the more familiar embedding
of grit on paper the lap is of high precision
particularly for flatness and turned by
a motor. (See faceting equipment)
The grit material is normally diamond and
sometimes corundum for their hardness.
Only diamond is hard enough on the Mohs
scale to shape and polish a diamond.
The initial shaping and facet placement
may be done using laps with the more familiar
grits of 220, 600, 1200.
The polishing step however requires grits
that are less familiar 8,000 14,000 50,000
and even 100,000. This grit is also embedded
into a metal lap, but sometimes applied
manually to the lap during polishing.
The faceting equipment allows for very precise
adjustment of angle and location of facet
placement around the gemstone referred to
as indexing.
The facet design may be computer generated
or left to the skill and experience of the
individual cutting the gemstone.
With the exception of diamonds a coolant
is constantly applied to keep the gemstone
cool since it is usually held in place on
the end of a dop using high temperature
shellac based wax or other adhesive. (The
dop in this case is a machined brass or
stainless steel rod)
Diamonds are held mechanically since the
heat generated by friction can be extreme
and will not allow the use of adhesives.
Cabochons, a smooth shaped gemstone without
facets such as jade or turquoise and most
gemstones are shaped and polished in much
the same manner, but are usually done by
hand relying on the skill of the individual
and the use of equipment similar to that
shown as lapping equipment
