synthetic corundum.7, synthetic ruby, gems

E.J. Gübelin describes microscopic features used to distinguish reconstructed rubies from natural rubies and synthetic material, relating their internal appearance to the fusion and subsequent cooling of natural ruby fragments. He argues that identification should concentrate on internal structures because reconstruction differs from both geological formation and the growth of synthetic ruby. Although the starting fragments are natural, their original inclusions, such as rutile silk, mineral crystals, and fluid feathers, should generally disappear during melting; preservation would be exceptional, chiefly where fragments were merely joined rather than fully melted. Conversely, the regularly curved growth striae characteristic of synthetic ruby need not occur because reconstruction does not involve the periodic deposition of molten droplets. Gübelin instead emphasizes irregular curved swirls formed within the viscous moving mass as it cooled and recrystallized. These can initially resemble features in synthetic ruby or even red glass, making preliminary determination of refractive indices, density, and absorption spectrum important. Closer examination shows that the swirls have strongly curved, unusually short radiating elements, arranged in groups that meet at sharp angles. Their marked irregularity contrasts with the comparatively parallel curved striae of synthetic ruby. Air entering the heated material produces abundant gas cavities, predominantly spherical but also elongated, angular, and unusually shaped. Some closely resemble the liquid-filled tubes, channels, and other cavities encountered in natural gemstones, creating a risk of misidentification. Gas inclusions may also combine into undulating veils or featherlike systems that imitate natural fluid feathers. Gübelin states that these deceptive formations are accompanied by individual bubbles and remain black when viewed from different directions, whereas natural liquid inclusions become transparent at a suitable viewing angle. A further feature described in cabochon-cut reconstructed rubies is a dense network of minute air-filled fissures immediately beneath the domed surface. He attributes this network to the release, during cutting, of internal strain generated by rapid cooling, and reports that comparable formations had not been observed in natural or synthetic ruby. The article presents the combined character of irregular swirls, abundant gas inclusions, deceptive featherlike arrangements, and subsurface fissures as diagnostic evidence of reconstruction, supported by examinations conducted in Gübelin’s Lucerne laboratory and illustrated by accompanying photomicrographs.