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 Post subject: Gray shades of blue and purple in Paraiba, paraiba type, etc
PostPosted: Wed Dec 16, 2015 2:37 pm 
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Hello again, I have been searching for something interesting to talk about that I may have not already covered on my own site, where I have been busy and hiding for the couple of years. It had to be about tourmaline of course.

Earlier I read that at least one member question whether a cuprian tourmaline in the correct range of colors for Paraiba, etc. , but has a gray overtone should be called a Paraiba. The consensus of the appraisers that responded was that it should not. Even to think that a grayed stone should be put into the same category, as a stone who's claim to fame is it's vivid glowing colors, was an attempt to lower the qualities that a tourmaline needs to be a Paraiba, paraiba type etc.

Now I am not a heater with their personal experience, but I have a spectrometer and I can "see" into the color of a gemstone and know why there is a gray over tone. With gray being a composite color and not associated with any specific set of wave lengths in the visible spectrum, there can be more than one way to have a gemstone be grayish. (This is not an exclusive property of composite colors.)

One of the ways is for the gemstone to be desaturated and have a grayish color such as some blue tourmalines have. Being desaturated means that the gemstone's color is not very pure and not how dark it is, which is measured with its tone value. With the spectrometer you can see that the absorption peaks, for the chromophores producing color in a desaturated gemstone, do not reach very high above the background absorption level of the gemstone. I believe that this type of gemstone is what the appraisers were thinking of when they commented about grading Paraiba, and paraiba type etc.

Generally this is NOT case for Paraiba and paraiba type gemstones. Rather than having relatively small absorption peaks, you have great absorption peaks, that have the potential to give a fine color to the gemstone, but their individual effect is modified by the gemstone's total set of chromophore's, absorption. In the case of Paraiba, paraiba type, etc. the principle chromophores are Cu2+ and Mn3+, both of which are strong chromophores in tourmaline. In a great blend of their absorption you can get amazingly saturated purples that I have not seen outside of cuprian. In other cases the red vector added by Mn3+ can just make that cyan color from Cu+2, grayish. It is threw the correct application of heat that the "true"cyan beauty of many Paraiba, paraiba type tourmaline, by reducing Mn3+ to Mn2+ and removing the red vector from the gemstone's color, is born. (A great discussion about heating Paraiba tourmaline, on GO, with a professional heater who had retired to Hawaii, lead to the revelation that even the best Paraiba tourmaline from Paraiba were heated, to get rid of just a hint of gray.)

So what do you have when you're examining a cuprian tourmaline that has the properties of a Paraiba or paraiba type or even a paraiba like gemstone, but has a grayish cast to its color. If there is a purplish cast, it probably is unheated. If it does not have a purplish cast it can still be unheated. (There is not essential reason to have any effect of manganese as a chromophore in tourmaline to make a cuprian tourmaline a Paraiba or paraiba type gemstone.) Finally, you may just have an unsaturated gemstone. Without a spectrometer and /or other sophisticated analytical instrument you do not know how to evaluate the potential of the gemstone and its value. (Whether a tourmaline should be heated or not, to effect its color, is a completely different issue.) You might assume that all Paraiba and paraiba type gemstones have been completely heated, but your eye can not tell you that. That grayed tourmaline just might be an unheated Paraiba, with the potential of being extremely valuable. (I have seen rough samples of unheated Paraiba from the first and most important find of cuprian tourmaline at the mine in the State of Paraiba, Brazil. It consisted of portions of two crystals, that had a medium dark toned, grayish blue color with purple overtones).

Bruce
BruceFryTourmaline.com


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Thu Dec 17, 2015 11:39 pm 
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bruce_tourm wrote:
Hello again, I have been searching for something interesting to talk about that I may have not already covered on my own site, where I have been busy and hiding for the couple of years. It had to be about tourmaline of course.

Earlier I read that at least one member question whether a cuprian tourmaline in the correct range of colors for Paraiba, etc. , but has a gray overtone should be called a Paraiba. The consensus of the appraisers that responded was that it should not. Even to think that a grayed stone should be put into the same category, as a stone who's claim to fame is it's vivid glowing colors, was an attempt to lower the qualities that a tourmaline needs to be a Paraiba, paraiba type etc.

Now I am not a heater with their personal experience, but I have a spectrometer and I can "see" into the color of a gemstone and know why there is a gray over tone. With gray being a composite color and not associated with any specific set of wave lengths in the visible spectrum, there can be more than one way to have a gemstone be grayish. (This is not an exclusive property of composite colors.)

One of the ways is for the gemstone to be desaturated and have a grayish color such as some blue tourmalines have. Being desaturated means that the gemstone's color is not very pure and not how dark it is, which is measured with its tone value. With the spectrometer you can see that the absorption peaks, for the chromophores producing color in a desaturated gemstone, do not reach very high above the background absorption level of the gemstone. I believe that this type of gemstone is what the appraisers were thinking of when they commented about grading Paraiba, and paraiba type etc.

Generally this is NOT case for Paraiba and paraiba type gemstones. Rather than having relatively small absorption peaks, you have great absorption peaks, that have the potential to give a fine color to the gemstone, but their individual effect is modified by the gemstone's total set of chromophore's, absorption. In the case of Paraiba, paraiba type, etc. the principle chromophores are Cu2+ and Mn3+, both of which are strong chromophores in tourmaline. In a great blend of their absorption you can get amazingly saturated purples that I have not seen outside of cuprian. In other cases the red vector added by Mn3+ can just make that cyan color from Cu+2, grayish. It is threw the correct application of heat that the "true"cyan beauty of many Paraiba, paraiba type tourmaline, by reducing Mn3+ to Mn2+ and removing the red vector from the gemstone's color, is born. (A great discussion about heating Paraiba tourmaline, on GO, with a professional heater who had retired to Hawaii, lead to the revelation that even the best Paraiba tourmaline from Paraiba were heated, to get rid of just a hint of gray.)

So what do you have when you're examining a cuprian tourmaline that has the properties of a Paraiba or paraiba type or even a paraiba like gemstone, but has a grayish cast to its color. If there is a purplish cast, it probably is unheated. If it does not have a purplish cast it can still be unheated. (There is not essential reason to have any effect of manganese as a chromophore in tourmaline to make a cuprian tourmaline a Paraiba or paraiba type gemstone.) Finally, you may just have an unsaturated gemstone. Without a spectrometer and /or other sophisticated analytical instrument you do not know how to evaluate the potential of the gemstone and its value. (Whether a tourmaline should be heated or not, to effect its color, is a completely different issue.) You might assume that all Paraiba and paraiba type gemstones have been completely heated, but your eye can not tell you that. That grayed tourmaline just might be an unheated Paraiba, with the potential of being extremely valuable. (I have seen rough samples of unheated Paraiba from the first and most important find of cuprian tourmaline at the mine in the State of Paraiba, Brazil. It consisted of portions of two crystals, that had a medium dark toned, grayish blue color with purple overtones).

Bruce
BruceFryTourmaline.com

Good info Bruce. I have quite a few Brazilian Paraiba's that have a grayish tone. Really pretty unattractive stones. I need to find someone to heat. Many years ago I heated a 2 carater myself and incinerated it.

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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Fri Dec 18, 2015 10:13 am 
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A bit more on heating Paraiba. The retired heater said that many pieces of Paraiba were overheated in the effort to get the best cyan blue color/removing gray. Overheating causes a reduction in tonal value of the tourmaline. I have also spoken to a dealer who had the retired heater work on his Paraiba rough. Many times the rough was heated over and over again with the commenserate risk of bleaching out the stone. In other words, the process of heating Paraiba tourmaline to get the optimal properties, is both complex, intereactive and prone to problems. I have wondered why the simple reduction of Mn3+ to Mn2+ should be complecated, but it is and that leads me to believe that there is more going on. In fact I am not sure that the complex interaction of all the coloring agents in Paraiba tourmaline is well understude. I hope to find out more about this with my spectrometer and I will be writing about the subject.

Bruce


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Fri Dec 18, 2015 12:00 pm 
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Did I mention how great it is to have you back, Bruce?


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Fri Dec 18, 2015 4:40 pm 
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Thank you Barbra for the welcome. It is now over fifty years since I fell in love with faceting and tourmaline. My support for research on tourmaline, my website brucefrytourmaline.com and my efforts on Gemology Online is dedicated to helping people find beauty in tourmaline. It has been and will continue to be a wonder quest.

Bruce


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Wed Feb 24, 2016 7:27 am 
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Dear All ,
i am new in this forum and this is my first post . My english might not be perfect but i hope that it will be ok . I was in Mozambique 8 years ago and i bought many tourmalines and i kept them and now i want to cut them and sell . I would like to have your opinions and advices . I will start with 2 pieces . The first one is a 41,185 carats blue /green tourmaline . I think it is a natural paraiba tourmaline .

Image

Thank you .

Regards .


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Thu Feb 25, 2016 4:22 pm 
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Welcome to Gemology on Line, Nasco, hopefully you won't feel that you have to be too quiet.

Eight years ago in Mozambique was a fine time to be buying tourmaline in Mozambique. But it is hard to know if you were lucky enough to buy copper bearing tourmaline or not without getting it tested by a gemological laboratory. It is after copper had been discovered in gem quality tourmaline from Mozambique and prices for copper bearing tourmaline had aready gone up above "regular" tourmaline. Most of the copper bearing that I bought after the discovery, that had not been sold to me as copper bearing, were yellowish green not bluish green. I will list some attributes of the rough that I think may help you reduce the number of stones you send to the laboratory to have tested.

1, The rough must be water worn completely.

2, Purplish tourmaline is much more likely to have copper than other colors.

3, The tourmaline does not tend to be strongly dichroic or even noticeably dichroic sometimes.

4, When cut the stones should have a "glowing like" quality to be a higher grade of copper bearing tourmaline.

5, Most copper bearing tourmaline from Mozambique are included with the pretty normal array of flaws
for tourmaline.

As I have said color is not a diagnostic quality for copper bearing tourmaline from Mozambique. A full compliment of colors in numerous tone levels is available and testing is essential to obtain the full value of the tourmaline . The preceeding list may help you increase your odds of finding a copper bearing tourmaline, in those you have tested. (The best way to have them tested is with a spectrometer in my opinion.)

Bruce


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Fri Feb 26, 2016 5:31 am 
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Dear Bruce ,

i want to thank you for your time and all the informations you gave me . I will start cutting the stone tomorrow and i will post the result next week . I went a month ago to AIGS Bangkok and wanted to get a certificate for this rough but they told me that they did not do that . I dont know why maybe because it was rough . I went also to GIA and GRS but they told me that it will take 2 months to get it certificated so i did nothing . As i said i will cut it and then get it certificated , then we will see if we have a winner .

I know exactly about which kind of stones you are talking about . A friend of mine have this parcel ( see below ) 560 grams of medium gem quality rough paraiba tourmalines from Mavuco ( Mozambique ) . As you said most of them are included .
Image


I would like to tell you that my rough tourmalines are not from Mavuco but from another area in Mozambique and i think that also we can get copper bearing tourmalines there . After getting some of my stones certificated we will know .
We will see .
Let me also get your idea about my second candidate . It is a purple pinkish tourmline that weight 84,785 carats . It come from the same area of the blue green tourmaline i post .
Image

Image

Image
Thank you .
Regards .

Nasco .


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Fri Feb 26, 2016 1:44 pm 
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My principle deal of African material has come to believe that there are other areas of Mozambique that have produced cuprian tourmaline. I presently have a small piece that is siginifcantly different from material that I have gotten from Mavuco and he believes came from a different collection.

I would love to examine your newest canidate for cuprian, but my old screen is not good enough to say much. I have found that I can tell the difference between a purple from copper/manganese and the purple you find in some Rubellites, most of the time.

One finally item, I have found green to be one of the most difficult colors to tell whether it has copper in it or not. I have a beautiful grass green round that just had to be colored with copper in my opinion, but my opinion carried little weight until my spectrometer confirmed it without question.

Bruce


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Fri Feb 26, 2016 8:51 pm 
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nasco wrote:
I went a month ago to AIGS Bangkok and wanted to get a certificate for this rough but they told me that they did not do that . I dont know why maybe because it was rough . I went also to GIA and GRS but they told me that it will take 2 months to get it certificated so i did nothing . As i said i will cut it and then get it certificated , then we will see if we have a winner .
Nasco .

Save yourself a lot of money. Get or borrow yourself a "Jeweler's Eye" and you can check all you stones in less than 10 seconds each.


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Sun Feb 28, 2016 8:48 am 
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Hello,
we are now sure that other ( " s " ) area (s) in Mozambique have copper in some tourmalines .
Both stones ( bluish / green and the pink purple ) are winners . I went yesterday at the 57 th BANGKOK GEMS & JEWELRY FAIR and get certifcates from GIT in 2 hours . Copper ( Cu ) element was determined in those 2 stones . I will buy a sprectrometer soonly ( Thank you Bill :) ) . So , definetly , roughs tourmalines can be tested by a sprectrometer ??? Or only faceted stones ??

I will go back to Mozambique soonly and then i will be able to update you about the areas where natural paraiba tourmalines come out of our mother land .

I made a big mistake by cutting the bluish green tourmaline in Thailand . Proportions and angles are bad . The bluish green is now 21,26 carats with the proportion of 18,36 *13,64*11,95 . So the stone is not glowing at all. To let you know what i exactly did , i will send you some pictures . I will send the purple pink one to Europe to get it analized by a lab to know exactly the percentage of Copper element in the stone , to be sure that the stone can be a canditate for the HEATING PROCESS . Any advice is welcome .
The brownish hue in the included part was affecting the real color of the stone also . The piece i get certificated is a 1,79 carats Orangy Pink copper bearing tourmaline .
Am i able to send pictures when stones are sealed in their certificates in the forum ?

Image

Image

Image

Image

Image

Image

I am sorry for the quality of the pictures , i am using my cell phone .
I will look also in this forum is this kind of blue/green cuprian tourmaline can be heat to enhance the " glow " , maybe already some posts are talking about .
Or maybe i just have to re cut it goodly and leave it natural ??

Nasco.


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 Post subject: Re: Gray shades of blue and purple in Paraiba, paraiba type,
PostPosted: Sun Feb 28, 2016 6:19 pm 
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Congradulations on finding copper in your material, but finding out where it came from could be a much bigger job. Good Luck With It.

The following are some ideas of mine that you might find useful.

1, The way prices are going with decent tourmaline, whether all your material has copper or not is not important when it comes to cutting it or not. I would get it all well cut.

2, You probably have not lost too much by having it cut in Thailand, because you now have a preform for someone to cut a decent gem out of. Still it was probably a waste of more money than it had to be.

3, You need more information about the material than whether you have copper or not to determine how "heat-able" it is. But most heating practices have been developed by trial and error, so I expect that is the way your material will be tested. Still it would be great for science to have spectrographic information on both heated and unheated material and perhaps help develope a consistant heat procedure.

4, I was not very successful in get spectrographic information on a couple of rough pieces of authentic copper bearing tourmaline from Paraiba. I believe the problem was with my light source and not the spectrometer. You need a lot of light to work with rough, but I don't have a lot of experience with rough. I cut everything of significanes and test the finished gemstones. It works.

5, I have heard that everything, including in essence all the purples from Paraiba were heated. The results varied greatly and many pieces were heated excessively and became realtively wash out. It was not a trivial exercise and reducing the impact of manganese on the color of the tourmaline was not the only factor. The whole heating of Paraiba and the research that was done, leaves questions unanswered.

6, From past experience pinks with copper do not heat well. There is not enough copper.

7, What conditions in the tourmaline you need to have to produce the best "glow like" look is an unanswered question. The rough unheated Paraiba I saw did not display any "glow", but that property is difficult to see in the rough. Not all cuprian/Paraiba/paraiba type/paraiba like material has a quality "glow like" presentation".

8, Finally, I read a research paper that discussed the properties of reddish tourmaline from an East African country that contained measurable amounts of copper. The concentration of the copper was so low that it had no decerable effect on the tourmalines appearance. As I have said before, copper is not that rare in tourmaline, at the trace level and below the level of being a chromophore.

Good luck with your adventure and I would truely love to have a few small samples to cut, examine with my spectrometer and broaden my collection of tourmaline from Mozambique. It is my favorate place for tourmaline. If you would consider a deal, please email me at brfry@consolidated.net.

Bruce


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