Trace amounts of chromium – and occasionally, vanadium – are responsible for the emerald’s green color. Most natural emeralds contain inclusions (flaws) and surface breaking fissures. Because of this, nearly all emeralds are treated by submerging them in an oil bath to enhance their apparent clarity. However, after a period of 2 or 3 years, the oil will evaporate, leaving the original imperfections on display. The use of oil is traditionally accepted in the gemstone trade, although jewellers should make the buyer aware that the gemstones have been treated in this way.
Naturally mined emeralds are very rare and therefore, extremely valuable. The finest emeralds come from Colombia and are cut within the country. Because of their rarity and the public’s demand for the beauty of an emerald, a significant amount of synthetic emeralds are now being produced.
It is therefore important when buying an emerald to determine whether the gemstone has been naturally mined – and if so whether it has been “oiled” – or whether it is a synthetic gemstone.