Without FT-IR Spectroscopy, You May Not Be Able to Tell
Diamonds are one of the most prized gemstones in the world. Because of this popularity and the high prices of quality gemstones, there is a large market for cheaper stones that resemble diamonds, as well as diamonds that have been treated to improve their appearance. These include high-pressure high-temperature (HPHT) diamonds and laboratory-grown diamonds formed by Chemical Vapor Deposition (CVD), techniques which have improved to the point that these products are nearly indistinguishable from natural diamonds.
Today, the identification of synthetic and treated diamonds has become one of the major challenges for the gem industry. The reasons jewelers must be able to distinguish between natural and synthetic or treated diamonds are both legal and ethical. Even though there may be no discernible difference between the two, a synthetic or treated gem is obviously less valuable than the real thing, and treated gems may actually require special care.
In the United States, the Federal Trade Commission has published guidelines regarding the disclosure of treated gems, and numerous domestic and international professional associations have similar guidelines.
The World Jewellery Confederation (CIBJO) for example, maintains a Code of Ethics as well as a Blue Book which defines terminology, classification, and ethical guidelines for diamonds, pearls and colored gemstones. Detecting these stones can be a significant problem for diamond buyers if these stones are represented as natural diamonds by unscrupulous sellers. FT-IR spectroscopy can be a useful tool for buyers and sellers to determine whether diamonds are natural and what type they are. FT-IR (Fourier Transform Infrared) spectroscopy produces an infrared absorption spectrum that represents a fingerprint of the sample with absorption peaks which correspond to the frequencies of vibrations between the bonds of the atoms making up the material.
Because each element is a unique combination of atoms, no two compounds produce the exact same infrared spectrum. Diamonds are unique among gemstones because they are composed of a single element (carbon), while virtually all other gems contain multiple elements including significant amounts of oxides.
The infrared spectrum of diamond is equally unique and can be used to easily confirm that a stone is actually a diamond. However, a diamond consists of crystalline carbon and the extreme conditions required to create them also provide a way for trace amounts of other elements to be trapped in the crystal matrix. The most important trace element is nitrogen, which can be found in different forms in the diamond crystal. These nitrogen aggregates create unique features in the infrared spectrum and are the basis for classifying diamonds into types. Type I stones contain nitrogen impurities while Type II do not. Other impurities, such as hydrogen, boron and carbonates are other important trace elements which have identifiable features in the infrared spectral region. The infrared peaks corresponding to the nitrogen aggregates or presence of other elements can be used to provide valuable evidence that a stone is not natural.
Learn about several diamond analysis techniques based on FT-IR spectroscopy that are extremely valuable to gemological laboratories.
[…] According to the Gemological Institute of America (GIA), most synthetic diamond producers are shifting to the CVD process because of its lower cost. This method also creates colorless diamonds closer in appearance and quality to natural stones, some of which are making their way into the gemstone market. GIA researchers have conducted tests on CVD-produced diamonds to discover signatures that can be used to tell the difference between CVD and natural diamonds. A previous article addressed how without FT-IR Spectroscopy, you may not be able to tell the difference between synthetic or natural diamonds. […]