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Colored Stone Grading - Crystal

Crystal: Richard Wise presents this concept in his landmark book, Secrets of The Gem Trade, so we’ll just quote his definition from his website:

"Crystal = transparency. In elder times, experts used the term water; if a gem was transparent with excellent color it was termed 'a gem of the finest water.' In the connoisseurship of very fine gems, both factors must be present to a superlative degree. A very fine gem always has a high degree of transparency. There are a number of factors that may affect crystal: many gemstones turn dark, sooty or muddy in incandescent lighting; inclusions, if they are dense and in large numbers, reduce transparency; color tone may also affect crystal. A gem that is overcolor (black) will rarely exhibit transparency.

Crystal is an attribute of all very fine gems, but it varies by species and variety. Almost any reduction in transparency is a minus. The exceptions: the characteristic milky glow in Kashmir-type sapphire will reduce crystal, but it will substitute that with another beautiful phenomenon, namely the glow. Star and cat's-eye stones require a certain type of inclusion to create the star or eye. These inclusions necessarily reduce transparency, but in this case substitute another beautiful phenomenon, namely the eye or star. In these examples, once the color and the strength and quality of the phenomenon is considered, crystal is next in importance". (See Secrets of the Gem Trade, Ch.4, pp. 39-44.)

In our system, crystal is mentioned only when, in our opinion, it applies. As Mr. Wise himself points out, crystal is a superlative that will only apply to the very top grades.