Swiss Blue Topaz is a form of white topaz that has been treated; irradiated and heated. Natural blue topaz does exist in nature but is very rare and expensive, so most blue topaz on the market has been treated in this way. Swiss Blue Topaz is an intense shade of vibrant blue and it demonstrates superb clarity, even in large sizes. Treated blue topaz comes in two other shades; Sky Blue (light) and London Blue, which is a medium to dark greenish to grayish blue. The colour depends on the treatment time, and Swiss Blue falls between the other two in terms of the length of time it takes to treat and the time it takes to cool off; for the radiation to dissipate. This period is around 6 months for Swiss Blue and this has meant that the price of this material has been steadily rising over the past couple of years. All of my blue topaz is treated in the US in line with safety guidelines there, so it is all completely safe.