Enhancement of gemstones – Part I

Luster or fire, color or lack of color, iridescence, opalescence, asterism and chatoyance (cat’s-eye or star effect) are some of the unique properties that increase the beauty and value of a gemstone. Since the beginning of civilization jewelers have increased their profits by using various means of making gemstones appear more attractive and valuable. In Harappa and Lothal, sites of the Indus valley civilization, archaeologists have uncovered pieces of agate and carnelian that were cooked in charcoal furnaces to change their color and enhance their appeal. Even in the ancient cities of Egypt, Ur, and Babylon, gem traders commonly practiced some kind of gemstone enhancements. Egyptian payrii describe some of their techniques, as for instance, how pearls were bleached by passing them through the intestines of a live cock or by soaking them in slaked lime. Verdigris and vinegar, oil and calves bile formed part of a process to make Emeralds. Various gemstones of Indian origin found in the tomb of Tutankhamen indicate that Indian traders of that time were experts at improving gems. Practitioners of the art of treating gem kept their treatment recipes, even those based on deception, as very closely guarded secrets then, as they do even today.

Colored stones, as all stones other than diamonds are termed, account for about a fifth of the huge gemstone trade. The supply as well as the price in the colored stone market is dictated by demand, availability and ethnic considerations, all driven by greed, fashion and illusion. Large clear specimens of good colors are exceedingly rare and cannot be valued by any formula; their price is determined entirely by negotiation. It is therefore only natural that even today, improved, simulated or imitation gems continue to defraud customers. The gems that stud jewelry are sometimes backed with metal foil, cloth, butterfly wings, and peacock feathers to increase their luster. Doublets and triplets where a genuine but thin stone is glued to cheaper material to increase the weight and luster are common, especially in Opals. Synthetic emeralds are grown over natural quartz to simulate a large and much more valuable emerald. To uncover such fakes, a recognized laboratory should carry out tests to detect such other fraudulent methods.