◆Enhancement on sapphire by heat

  Enhancement by heat is widely applied not only to blue sapphire but also sapphires of any colour. Like natural ruby, universal inclusion seen in natural sapphire is rutile caused by exsolution. In unheated stones, elongated needle-like rutile inclusions are observed more often than in ruby. Such rutile is observed as clearer scatterers on laser tomography (photo-12). 		Zonal structure generally seen in an unheated stone is indistinct (photo-13), but the minute scatterers that aggregate in a certain area show clear sector boundaries and they become a universal character to heated sapphires (photo-14 and 15). If the minute scatterers particularly show distinctive triangle outlines, it can be regarded as a characteristic feature of heating (photo-16).
Photo-12: Needle-like scatterers seen in an unheated blue sapphire. Photo-13: Minute scatterers seen in an unheated blue sapphire.
Photo-14(left) and 15(right): Minute scatterers aggregating with distinctive sector boundaries seen in an heated sapphire.
Photo-16: Scatterers showing distinctive triangular pattern seen in an heated sapphire.


Some unheated blue sapphire may show red fluorescent figure, but heated stones more frequently show red fluorescence throughout the stone. Also, as with ruby, dislocation generated by heating may be observed (photo-17a and 17b).
 Another typical fluorescent figure of heated sapphire on laser tomography shows distinctive triangular outlines with red, yellow and orange colours (photo-18 and 19).
Photo-17a: Minute scatterers in an unheated sapphire.
Photo-17b: The same stone shown in 17a, after heat enhancement. Red fluorescence is intensified, and dislocation appears.
Photo-18(left) and 19(right): Fluorescence figures showing distinctive triangular outlines with red, yellow and orange colours, typically seen in heated sapphire.


  This and the last issues introduced laser tomography. We believe that we could convey the importance of structural observation which reflects growth environment or history of a crystal in gemstone identification. Synthetic stones have been grown under regulated environment thus they have characteristic types and distribution pattern of defect that differ from those of natural stones (for instance, seed crystals in synthetic amethyst or growth stripes in synthetic alexandrite that were introduced in the last issue), and those characteristics can be a definitive proof in distinguishing between synthetics and naturals. In other case, as with corundum, when condition of defects or impurities in a crystal is changed by enhancement with heat, comprehending the change enables you to determine whether a stone is heated or unheated.
Observation of imperfection or inhomogeneity in a crystal such as lattice defects, growth stripes or growth sectors in various order becomes inevitable in gemstone identification, which is going to be more complex in order to detect very ingenious synthetic stones that is concerned to show up in the future, or to detect treatment process using the most-advanced technology. The effectivity of laser tomography will continue to grow as a means to obtain such information.
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