|
FIRE IN THE EARTH
|
||
|
|
||
|
in South Africa. It is valueless for ornamentation, lacking planes of cleavage, but is of great durability.
We
have been talking about diamonds in the use of tooling and cutting but
have paid little attention to the oldest form of it. You see the
itinerant glazier, perhaps, walking around with his load of sheet glass
seeking broken windows to replace—or perhaps you don't. Well, the
importance of the diamond in the glass-cutting industries of Belgium,
France, the United States and England is beyond doubt. Although many
substances, and nearly all the gem stones, will scratch glass, diamonds
alone can be satisfactorily employed to cut it along a definite edge.
Similarly, any fragment of diamond will cut glass, although possibly
with a jagged cut, but with a suitable diamond one can plane curls off
a glass plate as a carpenter's tool planes shavings off a deal board.
It is a popular but mistaken idea that glass should be cut with the
point of a diamond. The best results are obtained by using the girdle
or ridge lyine between the two points.
The
best-quality glaziers' diamonds are natural stones, each of which has
six distinct points, thus providing many cutting edges. The smallest of
these stones run about 80 to the carat, equivalent to a weight of less
than 0.04 grain each, but even these minute objects can be had with six
points—which cannot, however, be detected except by the expert, aided
by a magnifying glass. Stones of this quality are scarce and their
value is consequently high. Professional glass cutters usually set
their own tools and, when one edge has been worn, reset the stone until
all the edges give full service.
The
uses of diamonds in optical work are varied and many. They are chiefly
used in slitting of glass and porcelain by rapidly revolving copper
disks charged with diamond
(248)
|
||
|
|
||