Analyzing gemstones using infrared spectroscopy | Spectroscopy Solutions
The demand for gemstones is increasing, and fraudulent gemstones are becoming a prominent and difficult-to-tackle problem in the gemstone and jewelry industries. Fake, synthetic, and enhanced gemstones can be identified quickly and with confidence using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).
Gemstones, such as diamonds, pearls, sapphires, tourmalines, opals, and tanzanite, are naturally occurring mineral crystals that have been cut and polished.
The emergence of wealthy middle classes in rapidly growing economies such as China and Brazil mean that the demand for gemstones is strong, and regulation has struggled to keep up. This means that the sale of fake and fraudulent gemstones has skyrocketed and there is a need for a fast and effective way of determining authenticity.
The price of gems depends on their identity, origin, color, clarity, weight (carat), size, shape, treatments, cut and polish. Some of the rarest gemstones, such as the red diamond, can fetch up to $1 million per carat.
Naturally occurring, large, flawless gemstones are often the most valuable but are also the rarest. With natural, unenhanced gemstones fetching such high price tags, analytical methods that can identify fraudulent gemstones are in high demand.
What Makes a Gemstone Fraudulent?
Fraudulent gemstones range from outright fakes made from plastic or glass, which are usually easily identified by experts, to treated or synthetic gemstones which can be tougher to spot.
Synthetic gemstones share the physical, chemical, and optical properties of natural gemstones but they have been grown in a laboratory rather than formed naturally. There are synthetic versions of all the popular gemstones, and they can be difficult to identify. Synthetic gemstones are often perfectly clear, without inclusions, and have a deep color. Synthetic gemstones can be equally as beautiful as their natural counterparts, but they can be distinguished from natural gemstones by the lack of inclusions present in natural gemstones.
Treatments or enhancements can be performed on gemstones to improve their appearance. Some enhancements are common place in the gem industry. For example, most rubies and sapphires are heat treated, which is probably the most common form of gem enhancement. Other methods of gem enhancement include irradiation, diffusion treatments, dyeing, bleaching, impregnation with resins, oiling, filling, and coating.
An electrical furnace being used for high temperature heat treatment.
Synthetic and treated gemstones are still high-value, popular commodities as long as their origins are fully disclosed. Enhancing gemstones can alter their value either up or down. For example, if by modification an unusable gemstone becomes attractive and useable the value will likely increase, despite the fact that the gem has been enhanced. However, ‘useable’ untreated gemstones tend to have have much higher values than treated gemstones. For this reason, it is easy to see why fraudsters may attempt to pass off synthetic or enhanced gemstones as natural, untreated gems.
Some enhancements are widely accepted within the gemstone industry and by consumers, however these enhancements must always be disclosed to ensure that a sale is not considered as fraudulent.
Modifications that occur without the consumers knowledge are deemed as fraudulent. Such misleading practices are very prevalent in growing economies and can occur on a large scale. For example, in 2001, large quantities of a rare, pink-orange sapphire known as padparadscha began to appear in the Asian gemstone markets. Scientists identified that the gems were, in fact, cheaper sapphires that had been treated with beryllium and then fraudulently sold as padparadscha. A scandal ensued, and the sapphire market took a serious hit.
How are Fraudulent Gemstones Identified?
Gemologists use tools including jeweler’s loupes, microscopes, or measurement of the refractive index to identify synthetic gemstones or those that have been enhanced. A jeweler’s loupe is a magnifying device that allows inclusions and blemishes to be seen. Microscopes provide further magnification and can be used to detect heat treatments and other clarity enhancements.
However, these techniques all require a trained gemologist to carry out the analysis, and the decision always involves human error. In addition to this synthetic gems and enhancements are becoming increasingly sophisticated making traditional methods unreliable. As a result, advanced methods of gemstone analysis, which are borrowed from analytical chemistry, are becoming popular.
Infrared Spectroscopy for Gemstone Analysis
Identifying synthetic, enhanced, and fraudulent gemstones can now be achieved easily and rapidly using affordable equipment. Vibrational spectroscopy including is becoming increasingly important in the field of gemology. Reflectance infrared spectroscopy techniques, such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), are particularly useful for gemstone analysis as they are rapid, simple, highly accurate and the equipment required is low-cost and robust.
An infrared DRIFTS spectroscopic beam hitting a sample
DRIFTS allows the intrinsic structural vibrations of gemstones to be observed by reflecting an infrared beam off the surface of the material and detecting the reflected infrared light. The analysis is non-destructive and can even be performed on mounted gemstones. The obtained infrared spectra are compared with reference spectra to identify gemstones, determine whether the stone is synthetic or natural, and identify the presence of polymers, waxes, coatings, dyes, or oils used during enhancements.
DRIFTS accessories for gemstone analysis
Reflection infrared spectroscopy is typically conducted using an FTIR spectrometer combined with an accessory that enables reflectance to be measured. Specac offers a range of reliable reflectance FTIR accessories suitable for gemstone analysis including the MiniDiff and Selector DRIFTS accessories. The Selector is a flexible DRIFTS accessory, while the MiniDiff is an economic, pre-aligned DRIFTS accessory that allows easy analysis. Both of the Selector and the MiniDiff offer a easy, universal, and simple solutions for gemstone analysis.
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| Specac’s Selector accessory is offers highly sensitive measurements, 'selecting' only the truly diffuse components of the reflection. | Specac’s MiniDiff accessory is pre-configured for immediate DRIFTS experiments, providing jewelers with an easy and effective way of assessing the authenticity of gemstones. |
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The fraudulent sale of gemstones is an increasing problem that requires robust, affordable, and simple analysis techniques. No analytical technique can solve every problem or detect every gem enhancement, but DRIFTS can provide rapid, simple analysis of gemstones and give an indication of whether a gemstone is fake, natural, synthetic, or enhanced.
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