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SYNTHETIC GEMSTONES
Synthetic gemstones are made in laboratories or
factories, not in rocks. They have virtually the same chemical composition
and crystal structure as natural gemstones, so their optical and physical
properties are very similar. However, they can usually be identified by the
differences in their inclusions. Many gems have been synthesized in the
laboratory, but only a few are produced commercially- generally for
industrial and scientific purposes. |
PREPARATION OF A SYNTHETIC GEMSTONE
Man has tried to replicate gemstones for thousands of years, but it was not
until the late 1800s that any substantial success was achieved. In 1877
French chemist Edmond Fremy grew the first gem-quality crystals of
reasonable size (see bottom right), and then around 1900 August Verneuil
devised his technique to manufacture ruby. With a few modifications, the
Verneuil "flame-fusion" method is still in use today. The powdered
ingredients are dropped into a furnace and melt as they fall through a flame
hotter than 2,000°C (3,630°F), fusing into liquid drops. These drip on to a
pedestal and crystallize. As the pedestal is withdrawn, a long, cylindrical
crystal, which is known as a boule, forms. |
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flux - melt technique
Pioneered by the French chemist Edmond Fremy, the
flux-melt technique is still used to make emeralds. The powdered
ingredients are melted and fused in a solvent (flux) in a crucible. The
material must be kept at a very high temperature for months, before
being left to cool very slowly. |
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EDMOND FREMY
The first to grow emerald crystals of a reasonable size, French chemist
Edmond Fremy went on to grow ruby crystals by melting aluminium oxide
and chromium in a crucible. |
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SHAPES AND COLOURS
Because of the way they are made,
synthetic gems may show subtle differences in shape and colour that help lo
distinguish them from their natural counterparts. For instance, corundum
produced by flame-fusion has curved growth lines, rather than straight ones,
because the ingredients have not mixed together fully. Some synthetic gems
may also suffer from uneven colour distribution. Flame-fusion spinel is
manufactured to imitate gems such as ruby, sapphire, aquamarine, blue
zircon, tourmaline, peridot, and chrvsobery. |
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DISTINCTIVE INCLUSIONS
Synthetic gems have different inclusions from natural
gems, so often the best way to tell them apart is to examine them with a
loupe (below) or a microscope. Synthetic inclusions may be typical of a
process, or of a synthetic gem species. For instance, in Verneuil rubies,
gas bubbles have well-defined outlines; in flux-melt emeralds (right),
characteristic "veil" and "leather" patterns form. |
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GILSON GEMS
Lapis lazuli, turquoise, and coral produced by the French
manufacturer, Gilson, are similar to their natural counterparts, but are not
true synthetics because their optical and physical properties differ from
the natural gems. Gilson lapis lazuli, for example, is more porous and has a
lower specific gravity. |
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Natural Gemstones |
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