Simulants and Imitations
Although there are a number of materials which can have a similar appearance to ruby and sapphire (such as certain spinels, garnets, beni- toite, etc.), all are easily separated by reference to the properties, such as RI and SG.
More dangerous are assembled stones, generally consisting of one or more parts of natural corundum, attached to other materials (generally synthetic corundum). They may show natural inclusions and colours because they are part natural. The key to identifying any assembled stone is to locate the separation plane where the stone is joined together. It must be a distinct join, completely unbroken around the
entire stone. It is usually on the girdle, but may be on the pavilion or even the crown. The glue layer often shows curved brush strokes and flat gas bubbles. Since the glue’s RI is quite different from corun- dum, it will stand out in high relief when the gem is immersed in di-iodomethane.
Various kinds of assembled star stones are also possible. One of the most deceptive is simply taking a white star sapphire and coating it with red plastic.
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