Other topaz crystals, particularly those mined in Sri Lanka, are irradiated to make them blue. Radiation leaves the stones “hot” for several months, but the gems lose their radioactivity and are safe to wear after just a few months. Still, because of health concerns, topaz is often labeled to help consumers better understand what they are about to buy and how the gem’s hue was achieved.

Serious jewelry collectors don't put much stock in the common irradiated blue topaz used in bracelets, necklaces, and earrings, be they London, Swiss, or cobalt in hue. Some radiation-produced colors, especially yellows, can actually fade when exposed to sunlight, although this not a problem for radiation-generated blues. In fact, all topaz, even the untreated precious or imperial gems, are said to “bleed,” or lose color, in natural and fluorescent light.

Cut is another way jewelers bring out the normally quiet colors of topaz. Wide, step cuts such as an emerald cut expose the stone’s soft brilliance. As a less-expensive alternative to diamonds and sapphires, topazes are also given brilliant cuts in an attempt to mimic the look of their more sought-after cousins.

The relatively low cost of topaz has made it a favorite stone in showy rings and pendants, where the price of a similarly sized diamond would be prohibitive. Even larger examples of topaz can be found in museums around the world, which house topaz gemstones that have been cut into impossible-to-wear sizes.

One of the most famous of these monster gems is the American Golden Topaz, which resides at the Smithsonian Institution in Washington, D.C. This 10-pound stone of Brazilian origin boasts almost 23,000 carats and features 172 facets.

Smaller but more vivid is the 8,225-carat, cushion-cut Topaz Azul, which resides in the Programa Royal Collections based in Madrid. This stone’s Swiss blue is spectacular, but it was probably achieved by bombarding it with electrons in a linear accelerator, exposing it to neutrons in a nuclear reactor, and then heat treating it.

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