Blue topaz as it occurs in nature is quite pale in color and very rare. The incredible range of blues seen in the market today have all been produced by irradiation and heating of colorless topaz. This process is stable and the color is permanent. The three most poplular shades are known as:
Sky – light blue reminiscent of aquamarine
Swiss – vivid medium blue
London – deep intense blue
Blue topaz is one of the birthstones for December and is designated for the 4th wedding anniversary.