Pure topaz, like pure corundum, is transparent and colorless. The wide range of topaz colors that are available is due to either natural trace impurities or defects in the crystal structure. Color diversity is also caused by enhancements performed by the gemstone industry. Topaz can be found in colors including yellow, orange, brown, red, blue, pink, red, violet and green.
Colorless topaz is fairly common and is sometimes given a brilliant cut and sold as a substitute for diamond. Indeed, one of the most famous topaz gemstones in the world is a colorless topaz that was originally thought to be a diamond. It is a 1,680 carat stone known as the Braganza Diamond, owned by the royal family of Portugal. The gem apparently disappeared after the death of King John VI in 1826.
The most common colors of untreated topaz are pale yellow, brown and gray. Pastel shades of light-green, violet and pink are also found. Since these colors are rarely vivid, they are often treated to produce more exciting hues. The most popular color is blue. Indeed, blue topaz is the perennial top selling jewelry stone in the USA. Its combination of excellent brilliance, luster and clarity at a very attractive price makes it excellent value.
However, blue topaz occurs very rarely in nature, and then only in a very pale blue. The striking shades of blue topaz you'll find in the market are the result of widely-used enhancement techniques, usually involving irradiation followed by heating. These techniques produce a deep blue with a slight green tone, known as London blue; a highly saturated medium blue known as Swiss blue; and a bright light-blue known as sky blue.
The most valuable topaz color is an orange to pink color known as imperial topaz. The exact color for imperial topaz is not well-defined, so a wide range of golden orange, peach and pink colored topaz is sold under this name. Some light-pink topaz gems are the result of heat treatment.
Bright pink topaz is the result of another enhancement technique - a high tech process known as thin-film deposition. The technology involves depositing an extremely thin metallic layer only a few microns thick. This layer changes the optical properties of the material.
The thin metallic film is applied to the pavilion (bottom half of the gem), so that the interesting color effects are reflected through the crown. The film is molecularly bonded to the stone, effectively becoming part of the topaz. The range of colors is almost limitless, and include bright pink, electric blue and prismatic mystic topaz.
- First Published: December-17-2008
- Last Updated: October-07-2014
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