In
the early years of the African mines, dealers made large profits. The
market price in 1875 was about $4 per carat for fragments, and $10 for
crystals. It fell steadily to 40 cents to $1.50 in 1892. It then rose
to $4 to $8 in 1901, since which it has declined steadily again. Small
diamonds, or corners of crystals, having an edge suitable for glass
cutting and called " glaziers' diamonds," have a wide range of price,
selling from $6 to $50 per carat.
"
Flats " are thin crystals or parts of crystals into which holes are
bored so that they can be used as dies for drawing wire. In many of the
fine and delicate adjustments required now, in electrical machinery
especially, it is necessary that wire shall be drawn to a gauge
infinitesimally exact. Constant drawing of wire through metal dies,
even of the hardest, soon enlarges the hole, and consequently the size
of the wire also, but with a diamond die, enormous lengths can be drawn
without any appreciable difference. These tiny plates of diamonds have
therefore become valuable assistants in the progress of machinery and
its adaptation to applied science. They are sold now for $3.50 to
$8.00 per carat. The dies for which diamonds are used are for drawing
fine wires. The holes range usually from 0.001 inch to 0.064 inch,
though they can be made accurate to 0.0001 inch. The wear of metals on
diamonds
