His first breakthrough came in 1956, when he found the spectroscopic feature for detecting yellow irradiated diamonds. The spectroscope was a largely overlooked gem instrument at the time, but Crowningshield used it to examine every transparent gemstone submitted to the lab, meticulously drawing the absorption patterns with charcoal on paper. By examining the spectra of more than 10,000 natural-color and irradiated yellow diamonds, Crowningshield spotted the 592 nm absorption line that indicated irradiation treatment. It was a landmark contribution, one that also established the spectroscope as an invaluable tool in gem identification.
G. Robert Crowningshield Leading the Way in Gem Testing and DetectionPlay
In 1970, Crowningshield reported on the new laser drilling process used to bleach dark inclusions in diamond. A year later, after General Electric announced the development of gem-quality synthetic diamonds, he wrote the first scientific study of the material. During the mid-1970s, he examined hundreds of Tahitian black cultured pearls and determined they were of natural color, an important milestone in the trade’s acceptance of these products. His 1983 Gems & Gemology article describing the color nomenclature of orange-pink “padparadscha” sapphires is considered the authoritative explanation for these rare and highly prized specimens.
Over a span of four decades, Crowningshield published more than a thousand brief observations in G&G’s Lab Notes column, which he started in 1957.