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 Post subject: Re: Cuprian/Paraiba tourmaline
PostPosted: Sat May 01, 2021 11:33 am 
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1bwana1 wrote:
Tourmaline that has Cu is getting a premium price even if the color is ugly. Makes no sense to me. The reason Cu stones were originally desirable was that the Cu produce exception neon colors. An ugly stone is an ugly stone no matter the trace element in my opinion.


Burmese Ruby, Kashmir Sapphire, come to mind. Often the descriptive adjective trumps the quality of a gem.


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 Post subject: Re: Cuprian/Paraiba tourmaline
PostPosted: Mon May 03, 2021 2:54 am 
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1bwana1 wrote:
Interesting. Do you have an image of the GL-Spectrometer graph?


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Cuprian Tourm.jpg
Cuprian Tourm.jpg [ 97.98 KiB | Viewed 200 times ]
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 Post subject: Re: Cuprian/Paraiba tourmaline
PostPosted: Wed May 05, 2021 7:42 pm 
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"I believe that G.I.A. uses the GL-Gem Spectroscope, as do a number of other of the big labs. I have one of these in my lab and it works great."

I would be very surprised if they did. When I worked there in research we used a Hitachi 4001 UV-V-NIR spectrophotometer. I also ran many cuprian tourmalines on that machine. Other divisions had various versions of UV-V-NIR spectrophotometers. However, I did a lot of comparison testing between the $50K 4001 and Ocean Optics spectrometers back in early 2000 and in some cases they provided better data and were definitely faster.


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 Post subject: Re: Cuprian/Paraiba tourmaline
PostPosted: Wed May 05, 2021 7:58 pm 
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“The VIS-NIR digital spectroscopes that the labs like GIA use to make the call are only qualitative, not quantitative.”

It is interesting to note that the qualitative method that has sometimes been used in the past can lead to issues. A IIa diamond was defined by the absence of nitrogen in the FTIR spectrum. When I joined research, we used a Nicolet SX-60 FTIR but after a while we upgraded it to a Nicolet Magna 560 FTIR. The better sensitivity of the new instrument effectively changed the bar for defining a IIa diamond.


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 Post subject: Re: Cuprian/Paraiba tourmaline
PostPosted: Wed May 05, 2021 8:48 pm 
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Gemlab,

Thanks for posting that chart. i would definitely make the call as non cuprian based on that chart.

I have some stones that have a broad low hump at around the 900nm line. Usually I expect a much sharper peak there to make the Cuprian call. I am really not sure about these, so i was interested to see your chart. But, not the same at all.

Thanks for posting.

Steve


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