Tanzanite Heat Treatment; Is it a Quality Factor?

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Tanzanite Heat Treatment; Is it a Quality Factor?
Natural Tanzanite gemstone is a mix of grey, green, brown, and blue colors. The gem achieves its blue color through heat treatment. Most of the Tanzanites we see in the market are heated. The big question is does heating affect Tanzanite quality?
Heating can occur naturally before the gem is mined. The earth’s thermal vents have been heating Tanzanite deposits for millions of years hence some gems are mined being already blue in color. After mining, the gems are usually heat treated regardless, in order to remove any residual unwanted colors.
Natural Tanzanite gemstones can also be heat-treated to remove the brownish color and leave behind the blue and violet that we have all come to adore. Heating is done in temperatures ranging from 400 to 600 degrees centigrade for about an hour.
The Tanzanite heat treatment is very mild compared to the heat treatment of other gems like rubies and sapphires. Such gems can be heated to temperatures between 1000 and 1800 degrees centigrade and held at those temperatures for days or weeks.
Tanzanite’s color change through heating is not reversible and will remain unaffected by cutting and polishing. Be warned the color does not signify Tanzanite quality.
Are Heated stones more Valuable?
While heat treatment of Tanzanite may result in a more favorable color, it does not enhance the grade or value of the gemstone. If a piece of Tanzanite was medium-grade, heating will not enhance it to a top-grade Tanzanite. Heat treatment does not affect Tanzanite quality.
The value of Tanzanite will still depend on other factors apart from color. These are the 4 Cs of Tanzanite. Along with color, there are Carat, Cut, and Clarity factors that determine the value of Tanzanite.
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Will Tanzanite Heat Treatment Enhance Color Saturation?
The heating does not change the original color of this rare blue gemstone. It only removes the red/brown axis and leaves behind the desired blue/violet color. If the stone was originally pale blue, heating will not enhance it into a deeper blue.
When a medium-grade stone which is normally lightish brown is heated, it will become pale blue/violet. When a top-grade stone which is normally deep brown is heated, it will become a deep blue/violet after heating.
How to Distinguish Heat-Treated vs Unheated?
The main difference between a heated and unheated gem is the removal of the yellow color due to heating. However, it is known in the mining industry that some Tanzanite has been naturally heated and may show no yellow color when extracted.
Technically speaking, all gems are heated. Either through pre-mining thermal vent heating or post-mining in commercial jewelers. Heat treatment is a common practice and one should be expected.
The practice goes back centuries. Heat treatment is basically a continuation of the heating processes that occurred in the ground. In today’s heat treatment, the stones are heated at very high temperatures hence speeding up the heating process that would have taken years if the stones were to be left in the ground.
Only a very small amount of untreated gems with perfect color are found in the mine. This type of naturally blue Tanzanite has a much greater demand in the market as they are rare.
Without heat treatment, the world would be with fewer colored gemstones. Heating allows us to change off-colored stones into beautiful-colored ones.
Does Heat Treatment Affect The Quality?
It is currently impossible to scientifically test the nature of the Tanzanite’s treatment, whether naturally heated or man-heated. Since all gems have been heated in one way or another, there is no effect on price. It is a common assumption that all gems have been heated at some point.
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