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Synthetic Corundum
Early attempts with ruby proving relatively
straightforward, synthetic corundum soon began to be produced
in many different colors, not so much to imitate other types
of natural corundum (some of these colors do not occur naturally),
as to provide a highly effective, inexpensive ornamental material
or even to imitate gems of quite a different mineralogical
nature.
Appearance The varieties most often seen
are colorless, pink, various shades of yellow including brown-
or orangeyellow, and violet. More rare are gray-green stones
that turn reddish in artificial light. The colorless variety
was used in the past to imitate diamond; the pink is a good
imitation of pink sapphire; the yellows have mainly been used
to imitate topaz, although they are not very similar; and
the amethyst violet variety is normally-for some inexplicable
reason-called synthetic alexandrite, despite the fact that
it looks quite different from alexandrite chrysoberyl. The
' variety which changes color is intended to be an imitation
of alexandrite, but it is not a very convincing one.
These stones are given more or less all the
types of cu: used for colored stones, particularly those they
are designed to imitate, but the round, mixed cut is more
often seen than with natural stones.
These stones are often quite large (easily 5-15 carats or
more), except for the colorless variety, which generally appears
in small stones, which are harder to distinguish from diamond.
All the varieties of synthetic corundum have the characteristic
fine luster of natural corundum, although this is not always
shown to advantage in poorly cut stones.
Distinctive features These
synthetic corundums, which are all produced by the Verneuil
method, usually display characteristic growth curves, although
these may be barely visible, if at all, in the yellow and
orange-yellow varieties. They lack, of course, the typical
inclusions of their natural counterparts. Where they are used
to imitate a gem of a different mineral type, this can immediately
be detected by measurement of the physical properties.
Cost Very low, even for fine specimens.mond. On the other
hand, the dispersion of 0.065 is higher than that of diamond.
Production This involves the use of very advanced technology.
At present, it is only produced in the United States. Switzerland,
and the Soviet Union
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