Originally an extremely rare variety of topaz, blue topaz is the gemstone for a 4th anniversary. These days blue topaz isn’t hard to come by, thanks to treatment techniques first developed in the 1970s.
The vast majority of blue topaz on the market has been treated to achieve its colour. Pure topaz is colourless but different colours are produced naturally, depending on the impurities present.
Blue topaz tends to be divided roughly into three shades of blue: sky blue, Swiss Blue and London blue. Sky blue is the least saturated of the three and has the lightest tone. It’s closest in colour to an aquamarine. Swiss Blue is slightly darker and more saturated—the colour of a Carribean sea. London Blue is the darkest and most saturated. Its smoky petrol blue colour makes it an appealing consumer choice.
Sky Blue Topaz (image courtesy of Pixabay)
To achieve the popular blue colour, colourless topaz undergoes a combination of irradiation and heat treatment. The irradiation (the type of which varies depending on the result desired) changes the gemstone’s atomic structure. This affects the way light travels through the crystal structure and the stone will now absorb different wavelengths of light, changing its appearance to the human eye.
Swiss Blue Topaz (image courtesy of Pixabay)
When subjected to increasing doses of radiation, colourless topaz will in turn become brown, greenish-brown, brownish-blue and finally blue. Irradiation treatment is usually done at doses which leave the stone with both brown and blue colour centres. Since the brown colour fades at lower temperatures than the blue, the stone is then heat treated to achieve a strong blue colour.
This process mimics how nature works when underground deposits of topaz are subjected to radiation from naturally radioactive materials over millions of years. That’s why blue topaz is so rare in nature—it results from higher does of radiation that are not usually reached naturally.
As well as being the gemstone for a 4th anniversary, topaz is the birthstone for November. It also has a reputation among crystal healers as something of a gemmological cure-all. In times gone by, topaz was worn as a necklace to dispel enchantment, bring wisdom and chase away the blues. The ancient Greeks thought it could increase strength on the battlefield, detect poisons and even turn its wearer invisible! Mixed with wine, topaz was considered a cure for burns, haemorrhages, insomnia and respiratory difficulties.
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