A New Technique for the Analysis of Corundum Using Laser Ablation ICP-MS Application

A large percentage of rubies and sapphires undergo some degree of heat treatment to enhance their color and, as a result, to increase their value. As the majority of “processors” certify their gems as “heat treated”, this practice is accepted by the trade. Established treatment methods involve super-heating the gems to near melting point, around 2000 °C, and diffusing them with hydrogen. Dealers have established analytical methods to differentiate these stones from untreated natural or synthetic ones. With the market value of natural sapphires far outweighing that of both synthetic stones and natural gems that have undergone color-enhancing processing, it is important to be able to make this distinction. However, a new processing technique was developed that involves the addition of beryllium (Be) during the heat treatment stage, making the treated stones very difficult to identify. This technique has been applied to modify some corundum to resemble one of the most valuable colored stones: vivid orange-yellow gems known as padparadscha. Because some processors refuse to disclose the gems as “beryllium-diffused”, referring to them only as "heat treated", and because beryllium is difficult to detect by conventional gemological instrumentation, the price and demand for colored stones has weakened [1]. A New Technique for the Analysis of Corundum Using Laser Ablation ICP-MS Application Researchers at the Gemological Association of All Japan found that laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an extremely effective means of investigating the distribution of Be, and other impurity elements, across the surface of a finished gem. This information allows gemologists to identify the different types of processing applied to individual sapphires. However, more research is required to understand the physical mechanisms that give rise to the color enhancements.