ENHANCEMENT

The colour and appearance of natural and synthetic gemstones can be enhanced by methods such as oiling, dying, staining, foiling, heat-treating, iridating, drilling and filling. Heavily included gemstones, such as emerald, are oiled to fill cracks and give the stone a clearer appearance. Oiling has been carried out for more than 2000 years, and is an acceptable part of the business. Filling the cracks with oil, wax and stain may be temporary, but more long lasting resins have recently be introduced.

Oils and stains may leak and can be identified by wiping with a soft cotton cloth. Turquoise, Lapis Lazuli, Jade and Agates may be given a coating of wax. Agates are often stained to bright colours that have no natural counterpart and are therefore easily recognized as fakes, though some find them attractive. Placing a piece of foil behind a mounted gemstone to increase its fire and sparkle was a method used by Victorians, particularly for costume jewellery. Probably the oldest method of enhancing the appearance of a gemstone is by heating. In India, Carnelian has been heat-treated for more than 4000 years. Heating may be carried out in oxidizing conditions or in reducing conditions. Heat treating and irradiating gemstones can be used to change or enhance colour. For example, colourless and pale brown Topaz can be heat-treated to give blue Topaz. In addition lasers can be used to drill even the hardest diamonds to remove inclusions and the drill hole may then be filled.