Today I want to talk about blue topaz which is one of my favorite gemstones to work with. First a quick note about Topaz and its many colors.
Topaz doesn’t get its colors from chromophores like many gems. Instead, it has color centers which are defects in the crystal structure. Most Topaz are colorless or clear. However, there are some that do have color. Natural Blue Topaz is rare while heat-treated blue Topaz is common.
In the 1960s, a two-step heat and radiation lab treatment was used to enhance colorless Topaz or pale blue Topaz to make it more vivid. There are three types of Blue Topaz (the heat and radiated versions):
- London Blue. Dark and Steel-blue color.
- Swiss Blue. Highly saturated greenish-blue.
- Sky Blue. Pale blue that resembles aquamarines in hue and tone.
Different processes produce the following colors:
- Neutron bombardment in a nuclear reactor produces the deep, slightly greenish or grayish “London Blue.”
- Electron bombardment in linear accelerator results in the light, aqua-like blue known as “Sky Blue.”
- Combinations of both treatments produce the highly saturated “Swiss” and “Electric Blues.”
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