Gem Identification Goes High-Tech
Jewelers routinely buy and sell laboratory-grown gems like synthetic amethyst or stones with inscrutable enhancements like irradiated pink tourmaline, never quite knowing the true nature of what they’re dealing in. Some consider the problem unavoidable and little cause for concern. Yet, owing to the risk of lawsuits over misidentification and nondisclosure, more jewelers today are turning to professional gem labs for accurate identification.
For years that task has gone to the Gemological Institute of America’s Gem Trade Labs in New York and Carlsbad, Calif., as well as overseas labs in Geneva, London, and Bangkok. Equipped with state-of-the-art gem-identification technology, these labs have labored to keep up with growing demand. Smaller labs have tried to pick up the overflow, but few can afford the sophisticated equipment necessary to make consistent and reliable identifications.
With the opening of the American Gem Trade Association’s Gemological Testing Center in New York, there’s another place to turn. Director Ken Scarratt says that most of the equipment is in place, and he’s open and ready for business.
Gearing up. AGTA’s lab will focus solely on identifying colored stones, pearls, fancy colored diamonds, and enhancements to these gems. No diamond grading will be done at the lab. Colored gems and fancy colored diamonds will receive the most attention. But Scarratt sees pearls regaining some of the popularity they enjoyed in the 1940s and ’50s. “We’ve found a tremendous demand for pearl identification,” he notes. That’s right up his alley: Scarratt spent 18 years as director of the British Gem Trade Lab, where more than 90% of identifications were pearls.
A lab requires sophisticated equipment to identify all the possible gem materials, simulants, enhancements, and countries of origin. Since every gemstone has a specific chemistry, source of color, and method of growth, the devices necessary to identify one gem might not be helpful for another.
Take blue sapphire. A simple refractive-index reading can tell you whether or not the gem is a corundum. But it can’t tell you if it’s synthetic or natural, whether it’s been heat-treated, just how blue it is, or its country of origin – all of which contribute to the value of the gem. The AGTA lab is equipped with high-tech research instruments for six different types of analysis, enabling it to make these and other determinations.
X-radiography. Gem labs use X-rays to view the internal structure of a pearl. That way they can determine whether it’s natural or cultured (bead-nucleated), mantle-tissue-nucleated, or keshi (a byproduct of the fresh-water culturing process).
Most pearls that come to gem-identification labs are either mounted or strung. While various instruments can be used to identify pearls, Scarratt considers X-radiography the best way to attain conclusive results. X-radiography enables lab staff to view entire strands of pearls – even pearls graduated in size – with a single scan and obtain a readable film to make the identification.
X-radiography also enables Scarratt to measure the nacre thickness. That’s a key factor in determining the quality and origin of the pearl, which is especially important given the market proliferation of inexpensive, thin-nacred cultured pearls.
Energy dispersive X-ray fluorescence (EDXRF). X-rays, when used to stimulate fluorescence, can identify the chemical makeup of a gem. For example, EDXRF can differentiate natural fresh-water from salt-water pearls based on the former’s far-greater concentration of manganese.
EDXRF also plays a critical role in detecting enhancements. Because enhancements alter the chemical elements of a gem, it’s necessary for the gemologist to know what the gem’s chemistry should be so that it can be compared with what is actually measured. That helps determine the type of enhancement – whether heat or irradiation, chemical impregnation or stains.
Fourier transform infrared spectroscopy (FTIR). Unfortunately, X-rays can’t always tell you whether a gem is synthetic or natural. The best tool for that purpose is FTIR. Until a decade ago, it was difficult to identify certain synthetics because the visible light spectrum of a synthetic gem matches that of a natural stone. Now that there’s a way of detecting infrared spectra (beyond the visible red), the synthetic gem world has become an open book.
With infrared spectroscopy, labs can identify gems quickly and easily. Sophisticated software and delicate infrared detectors give today’s gemologists the means not only to distinguish natural from synthetic gems, but also to see specific spectrum-inducing impregnations, resins, plastics, stains, and irradiation enhancements.
Jade, for example, is well-suited for FTIR testing. Jade can be stained or impregnated, yet standard gemological tests such as magnification, UV fluorescence, and thermal testing can’t identify these enhancements definitively. B-jade, the polymer-impregnated jadeite, can be easily identified using FTIR.
FTIR can also be used for identifying emerald enhancements and synthetics, determining the origin of color (irradiated vs. natural) of fancy colored diamonds, distinguishing between synthetic and natural diamonds, differentiating amber or copal (“young amber”) from other resins, identifying amethyst vs. synthetic amethyst (a difficult task), and detecting natural from synthetic alexandrite.
Ultraviolet-visible (UV-Vis) spectra analysis. Labs use this technique to observe and measure the opposite end of the spectrum from infrared. The procedure helps identify the origin of fancy-colored diamonds. It’s also useful in determining whether a sapphire has been heat-treated and in identifying the country of origin of sapphires and emeralds. Technicians use UV-Vis analysis to identify whether a pearl is natural black or stained (dyed and/or irradiated).
Imaging spectroscopy. Imaging spectroscopy is the very latest technological breakthrough, used in only the most advanced gemological laboratories. With imaging spectroscopy, you can actually quantify the amount of color in a gem. That measure depends on the quality of saturation as well as the proportions and cut of the stone. This helps gemologists determine proper nomenclature, distinguishing, for example, ruby from pink sapphire.
Raman laser spectroscopy. This technique identifies inclusions, which can indicate a gem’s country of origin or its method of synthesis. Identifying inclusions unlocks the mystery of many gem formations and is especially useful in differentiating natural from synthetic stones.
Putting the data to work. To operate this equipment is one thing. To store all of the information gathered is quite another. So the computer equipment needed to run a modern laboratory is vitally important.
Among other things, labs require high-definition computer monitors as well as a Macbeth lighting system for accurate color rendition. After all, precise color rendition and description are critical in identifying colored gems, diamonds, and pearls.
All the latest high-tech equipment is ultimately worth little without the expertise of someone who knows how and when to use it. AGTA’s choice for director of its new lab was an astute one. As former director of the British Gem Trade Lab and Bangkok’s Asian Institute of Gemological Sciences, Scarratt has the requisite gemological and technical background. His years in London gave him extensive experience in identifying pearls. Added to that are his five years as head of AIGS, where 80% of the identifications were ruby, sapphire, and jade.
Gary DuToit, a specialist in Raman spectroscopy and one of Scarratt’s former AIGS colleagues, has followed Scarratt to New York. DuToit has written about determination of many inclusions, such as calcite in heat-treated Burma ruby and cedarwood oil in enhanced emeralds.
Rounding out the laboratory support staff is Mukda Clark, a Graduate Gemologist who also worked with Scarratt at AIGS. Clark has extensive training in the operation of all the scientific gem equipment.
Where the AGTA lab will make a huge difference is in the plain English of its reports. Gemstone identification reports from other labs are typically either too complicated or too brief, providing little or no explanation.
AGTA’s new reports have been tailored for each individual gem variety. Each report presents distinct identification results, a digital photograph of the gem, and enhancement identification. The reverse side offers easy-to-understand identification and enhancement definitions specific to the gem in question.
“Each gem has its own peculiarity,” notes Scarratt. “If we had just one report, with all of the enhancements listed, and then [had to] explain them all, we’d end up with a report the size of a small book.” Each report is color-coded to the specific gem (blue for blue sapphire, green for emeralds, and so forth). The lab uses “international nomenclature” to avoid misunderstandings among different languages.
The report, says Scarratt, “is geared to the customer.” His clients, he explains, want two things: “One is an accurate description. And the other is a paper that sells the stone. With our report, they can go hand in hand.”
For information on the fees and services of AGTA’s gem identification laboratory, contact the lab at 18 E. 48th St., Room 1002, New York, NY 10017; (212) 752-1717, fax (212) 750-0930.