JOURNAL OF CHEMICAL EDUCATION
590
A NEW METHOD FOR FINGERPRINTING DIAMONDS A. E. ALEXANDER Tiffany & Co., Fifth Avenue and 57th Street, New York, New York
ANOPTICAL instrument, invented by Brure Eyting6 and
placed, table facet down, on an optical glass flat. A developed by the Manhattan Research Laboratories of short distance below the glass plate is a holder on which New York, can, in a matter of seconds, photographically is placed a sheet of photographic film. Ordinary comrecord the light that is reflected from the back or pa- mercial film of the kind used for back-reflection X-ray vilion facets of a diamond. A spot pattern results, work can be employed, since this type already has a characteristic for each stone tested. circular hole in the center. The instrument (see Figure 1) consists of a metal Each pavilion facet reflects the projected light a t a cylinder a t the base of which is a fixed light source in the fixed angle, which in turn is impinged on the film. On form of a six-volt lamp. Parallel light is projected by a developing the film, a number of spots, more or less irsimple lens system to the diamond which is centered and regularly distributed, result. Since the facets of no two
NOVEMBER, 1951
591
diamonds of the same might and cut are ever fashioned absolutely (mathematically) alike, no two fingerprints of identical pattern are possible. If the stone is a different one, or if the original gem has for some reason been recut or relapped, a wholly different reflection spot pattern mill be obtained. Should the same stone be photographed a t somelater date, it is only necessary t,o superimpose one negative over the other to obtain a "mesh" or coincidence of spots. A ground-glass viewer of t,he kind used to examine X-ray radiographs is a valuable aid in examining fingerprint negatives. An exposure of four seconds is all that is required to obtain a spot pattern. The instrument will handle faceted stones other than diamond. Its most important use, however, is in the positive identification of diamonds. Diamonds of differcut cut, such as the brilliant, emerald, ant1 the marquise, give very distinctive fingerprints, as illustratrd by Figure 2. These spot patterns are useful in disclosing whether or not a diamond is properly proportiond Double refraction in a gemstone can be photographically recorded with rather spectacular results. Figure Figurs 2. Diamond Fingerprints 3 illustrates the marked double refraction of Zircon. Upper l e f t : brilliant cut. Lower left: marquise cut. Upper right: T o obtain this type of photo a different technique must emerald cut. Lower right: properly proportioned b?iuiant. he employed. In this case, the stone is placed table facet np on a small metal cylinder which can be adjusted several inches. 4 few seconds' exposure suffices t o 'egister the amount of d&hle rrfraction. A douhly refractive stone should be examined optically, or its indices of refraction carefully measured on a refraetometer using sodium light, to insure the obtaining of the gemstone's maximum double refract,ivit.y. The table facet of some doubly refractive gemstones may prove to he cut normal to an optic axis, in ~rhichrase no double refract,ion in this direction is possible.
4 Figure I .
The Eytinge Diamond Fingorprinte* with e Schemetic Diagram
to support the gem a t the girdle edge. (An old photographic diaphragm is very well suited for use as a stone holder.) The cvlinder most be carefully centered on the optical glass flat, over the opening through which the light beam is projected; otherwise di~tort~ion of the double refractive effect may occur. To achieve the maximum double refraction, such as is ~roducedbv Zircon, it is necessary that the culet facet of the gem be parallel to the table facet. The film in this instance is
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