| is quite simple. An alcohol lamp and a pair of tweezers is sufficient, as the following demonstration will show. The gold beryl is heated untill he changes its color. Heat it carefully, to avoid a temperature shock. The gold beryl resists good at this treatment and the resulting color is stable. The gold beryl becomes an aquamarine.
Note that the color intensity and saturations stay unchanged. A light yellow beryl will change to a light blue. It will not become darker or more intense in color.
Before treatment After treatment
Out of a group of 4 beryls we treated one to document the colorchange.
Normally this treatment is applied with an oven where you can control the temperature. Possibly more than one try is necessary. Each time the temperature is raised by 10°C. The stones to treat are usually preformed, to get rid of inclusions, as they may destroy the stone during treatment. Temperatures for rubies and sapphires may reach 1700°C.
A lot of stones react to heat treatment. The following reactions are possible:
| The color is modified | - Aquamarin - yellow tones disappear |
| - red Turmalin - brown tones disappear |
| - Tanzanit - brown tones disappear |
| - Amethyst - becomes yellow - Citrin |
| - Goldberyll - becomes blue - Aquamarin |
| The color is intensified | - Saphir - will clarify |
| - Ruby |
| The stone becomes lighter | - green Turmalin |
Heat treatment is applied everywhere also next to the mines. You have no warranty, that your stone is natural or non-treated when you buy at the mine. Gemstones are easy to transport. Therefore it is also possible that your stone bought in Madagascar is form elsewhere, for example from India, Bresil, Australia etc.
All treatments of gemstones must be declared to the customer, according the rules of CIBJO.
The American Gem Trade Association AGTA published a code to declare the different treatments. AGTA Gemstone enhancement charts.
Demonstration of the heat treatment by Katerina Kestemont.
Hubert Heldner April 2002
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