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Treatments of coloured gemstones |
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The colour and clarity of gemstones may be influenced, altered or improved by many methods of treatment. This is an everyday practice in the jewelry industry. Some of the treated gemstones must be handled more carefully. For instance, coated gemstones and those treated by diffusion cannot be recutted because the colour or the shape (e.g. light star) is concentrated only on the upper layer and is often very thin. Furthermore, oiled and filled gemstones cannot be cleaned by ultrasound.
The prices for treated and untreated gemstones are very different. The price for a brightly coloured untreated gemstone may be several times the price of a treated gemstone. The buyer of a gemstone has the right to get information regarding the fact and method of treatment and the necessary measures of precaution.
The treatments with gemological indications are divided into three classes and marked with the following letters:
| 1. |
N |
non-treated (untreated) |
| 2. |
E |
traditional treatments |
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H |
heated |
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O |
oiled |
| 3. |
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Non-traditional treatments: |
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B |
bleached |
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C |
coated |
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D |
dyed |
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F |
filled with a colorless compound |
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G |
gamma- or electron-irradiated |
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I |
infilled (e.g. with coloured glass) |
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L |
laser drilled |
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R |
neutron-irradiated |
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D |
treated by diffusion |
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W |
impregnated |
The geographic origin of a gemstone also affects its price. Everybody has heard that the Columbian emerald or the Burmese ruby is much more expensive than those originating from Africa. However, it is unnecessary to pay more for the “geographic pedigree”. High quality emeralds, rubies and other gems can be found at many sites all over the world and the gemstones from the famous sites are not always of excellent quality. The geographic site can be identified by the internal characteristics, i.e. on the basis of the inclusions in the gemstones if they contain any of them.
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