Fade Testing: Has The Time Come?

Kurt Nassau, Ph.D., FGA (Hon.), of Nassau Consultants, Lebanon, N.J., has long studied and written on the treatment and synthesis of gemstones. It's a widely accepted principle that gemological testing used to identify the precise nature of a gemstone material should be non-destructive. Yet there are exceptions. A close examination of any gemology textbook shows that some "slightly destructive" tests are acceptable for difficult gemological distinctions where no other approach can give the answer. These include the use of scratch testing to determine hardness, acid to identify carbonates, ether to distinguish amber from some of its imitations, acid and various solvents to identify the use of dyes and the hot-point to detect amber and wax impregnations. (Of course, the tests should be done in an inconspicuous area to minimize the damage.) Fade testing -- subjecting a gemstone to light
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