Experimental Instruments

Pitfalls in Color Grading Diamonds by Machine

“…Van Goethem (personal communication) has had the opportunity to test all the diamondgrading instruments reviewed by Read (1983). He finds that almost all instruments give a reproducibility that is the same or better than the human eye.…”

“…A number of laboratories have developed, and are developing, equipment with various degrees of sophistication for color grading diamonds. Read (1983) reviews those instruments that are available commercially. Although some techniques are believed to be reliable, others are lznown not to be.…”

The Gem Diamondmaster and the Thermal Properties of Gems

“…As quantitative instruments that permit better reproducibility and increased precision of measurement are developed, this property may be particularly helpful when used with refractive index measurements in distinguishing between various members of such groups. Gemtelz Gemmological Instruments manufactures the Gemmologist, a thermal device reported to distinguish between many colored stones as well as diamond (Read, 1983). To the author's knowledge, this is the only instrument specifically designed to have the increased sensitivity for effective measurement of colored stones.…”

The alexandrite effect of theTavernier diamond caused by fluorescence under daylight

“…The major improvement of this instrument was that the diamond was placed at the center of an integrating sphere. 10 At the present time, several colorimeters and spectrophotometers have been developed for color measurement of diamonds and other gemstones, such as the Kalnew Gemcolour 2 spectrophotometer, the Zeiss-Gübelin spectrophotometer, the Gran colorimeter, the Austron diamond colorimeter, the spectrograph CCD system being constructed by GIA Research. All current instruments utilize an integrating sphere.…”