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Optical Properties

Physical Properties

Synthetic Gems

 

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 2,000C (3,630F), 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 As the pedestal is withdrawn, a long, cylindrical crystal, which is known as a boule, forms.


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.

 

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.


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.

 

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.

 

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.

 

   

Natural Gemstones

 

 


 

   
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