Most emeralds -- even in the fine jewelry industry -- are oiled as part of the post-cutting process. This improves clarity and stability. Bead-quality emeralds are almost guaranteed to be oiled, with either a natural or synthetic oil with refractive index close to that of an emerald. With bead-quality emeralds, the oil may have added color, although this is not acceptable with higher-grade emeralds. When cleaning emeralds of any quality, clean only with a soft cloth. Avoid tumblers, ultrasonic cleaners, and harsh chemicals.