Using Spectroscopy in Advanced Gem Testing

Nowadays the gem market is increasingly employing photonics technologies to meet the demands of the fine jewelry and gem industry. This is due to the fact that the technology used to produce synthetic gemstones makes it difficult for the gem market to identify treatments applied to stones. Also, it’s difficult to identify and classify natural versus synthetic gemstones, and, in certain cases, identify the place of origin of a stone.

Emerald is a gemstone in the beryl family of minerals. Emeralds can be found worldwide. To date, Brazil, Colombia, and Zambia are some of the largest areas known for emerald production. It has characteristic deer green color because of the presence of iron and chromium. Due to surface fissures, emeralds that are commercially available are oil treated with cedar oil, which possesses a similar refractive index.

The late 1800s saw the advent of synthetic stones, and in the 1930s the production of the first artificially produced emeralds that were large enough for gem cutting. Two methods are available for producing synthetic emeralds:

  • Hydrothermal growth (it uses pressure and heat to imitate the conditions created in the Earth’s crust);
  • Flux-fusion method (this method uses a flux, or a heated solution of minerals, that forms crystals upon cooling. It is a time-consuming method and suitable crystals require approximately one year to grow).

New and increasingly refined synthetic gems have been introduced since the 1990s, which more closely imitate the physical characteristics of natural emeralds.

Such synthetic emeralds are similar to natural counterparts and share almost all of their optical, chemical, and physical characteristics. These stones cannot be distinguished by the naked eye. The sale and marketing of synthetic gems are regulated by the Federal Trade Commision and requires disclosure of a gems origin and composition.

Firstly spectroscopy was used for studying minerals and gems soon after Isaac Newton attempted to separate sunlight into its component colors with the help of a prism. Researchers began to map the solar spectrum and started to detect absorption spectra for many common elements present in gemstones.

The Gemological Institute of Valenza and Italian researchers from the Department of Earth and Environmental Science at the University of Pavia have published a study on the characteristics of synthetic and natural emerald using the spectrometers for broadband reflectance measurements. This spectroscopic method provides the biggest advantages for gem analysis. In addition this, spectral data can be obtained rapidly, and this technique has been tested under usual laboratory conditions.

Spectroscopy is used for identifying synthetic gemstones, as well as, for detecting gem treatments or identifying the origin of stones that may come from conflict zones. Raman spectroscopic measurements are favored by some spectroscopy applications for gemology.

Optromix Raman fiber optic probes are miniaturized without compromising its performance, which is enabled by the technology of direct deposition of the dielectric filters at the fiber end faces. In results in a small, cost-effective Raman probe for different Raman systems and, for example, for endoscopic and other applications.

The fiber optic Raman probe is produced for multi-wave excitation in the range 690-785 nm and 1000-1064 nm, e.g. @785 nm  – “Fingerprint” spectral range with fluorescence reduction, and @690 nm – “High wavelength” spectral range for conventional Raman spectrometers.

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