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 Post subject: Ametrine treatment enhancement
PostPosted: Mon Oct 25, 2010 2:32 am 
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I wonder, can you help me please? I’m trying to locate any information relative to the treatment/subsequent enhancement of NATURAL Ametrine. Is it or can it be, perhaps, heat treated/irradiated to enhance its colour?
I know synthetic Ametrine has been produced in the RFSFR. But do people try any treatment to either darken or lighten the colours of natural ametrine.

I have quite a collection of Ametrine purported to be from the Anahi mine – some shows lighter colouring (yellow violet), other pieces are quite dark yellow violet.

All that I have has a gentle gradation across the colour change band (I know that the synthetic material has a sharply defined boundary between the colours.

Many thanks, Lassuuu


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 Post subject: Re: Ametrine treatment enhancement
PostPosted: Mon Oct 25, 2010 12:17 pm 
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A little background on ametrine.
Image
Image courtesy of
Dalan Hargrave
Second place, Cabochon Gems
Symmetry, cross-section of natural ametrine from the Anahi mine in Bolivia, backed with mother-of-pearl. 22 mm x 19 mm. 37 cts.
Photo: Phillip.

Ametrine was originally described as a curious find in 1980. (Hehar, Koivula, Vargas, 1980). It's locality was originally given as Rio Grande do Sul in Brazil, but later determined to be in Bolivia. The material met with immediate suspicion, as Kurt Nassau had a synthetic example of amethyst/citrine in his collection for several years prior to the "find" in 1980.

Several unsuccessful tests were conducted in order to see if this bi-colored quartz was actually the result of a series of treatments. Then, it was discovered that specimens of a specific sectored amethyst from Minas Gerais, which exhibited alternating sections of dark and light amethyst, could indeed be altered to ametrine. This was done with a succession of heat treatments followed by irradiation coupled with subsequent annealing.(Gems & Gemology, Spring 1981).

The results of this experimentation made "naturally occurring ametrine" suspect and controversial at best. Ametrine, in the 80's, was presumed to be 100% the result of treatment.

That all changed when the Anahi Mine in Bolivia was shown to produce vast quantities of naturally occurring ametrine, (insert egg on face), in the early 90's. Between 1989-1994, 100 tons of naturally occurring ametrine xls were extracted from the Anahi Mine. (G&G, Spring 94).

This is a valuable lesson for gemologists. We must be careful when extrapolating experimental evidence.
[-X "Just because something CAN be done, does not mean it IS being done."


As mentioned earlier, there were examples of bi-colored, synthetic, amethyst/citrine in existence in the 70's, but it was not until 1994 that Russian synthetic ametrine was available for commercial distribution. These crystals were being produced by hydrothermal growth from alkaline solutions. We are able to separate the synthetic material from natural on the basis of growth features (twinning and color zoning), sophisticated EDXRF chemical analysis and IR spectral analysis. (G&G Summer 1999)

From reading these three articles, I am not getting the sense that subjecting ametrine to additional heating, irradiation and annealing will improve it's saturation of color, but I have no empirical evidence to back up that opinion.

Further information from Caltech, by Dr. George Rossman


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 Post subject: Re: Ametrine treatment enhancement
PostPosted: Mon Oct 25, 2010 3:59 pm 
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Thank you. That is helpful. My material was all bought post 2007. The Anahi mine is still operational so presumably much more material has been mined since 1994. I have one specimen of synthetic ametrine to make comparisons with. It shows an exceptionally sharp dividing line between the colour bands readily seen either by eye or with a loupe. Lassuuu


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