corundum, treatments.6, gems

CMS: The Swiss Gemmological Institute (SSEF) in Basel has found its recent acquisition of a Raman microscope well worth the investment, to judge by this excellent account of its initial applications at this laboratory. Much more accurate, easier to use, and considerably less expensive than its predecessors, the Renishaw Raman microscope at SSEF easily fits on a desktop. It has enabled SSEF staff members to identify CO₂ inclusions in sapphire that are diagnostic of heat treatment, detect and identify fracture fillings in emerald, easily identify mounted gemstones, and characterize specimens with irregular surfaces. It can also distinguish component minerals in many aggregates. The method is nondestructive in all but a few well-documented conditions and works on all types of materials, except those having simple compositions and high symmetry, such as metals and alloys. Raman spectroscopy does require that the user be aware of its limitations and parameters; also, the lack of a large, published database means that each laboratory must obtain many of its own reference spectra from known samples. However, Raman spectroscopy clearly has earned a place of respect among the few high-tech laboratory techniques that have proved indispensable to gemological testing today.