Description: heat-treatment process - Nigerian Tourmaline

[Arcadian]

Re: Description: heat-treatment process - Nigerian Tourmalin

Hi Roger, thanks for showing this! Thats a pretty cool process, and wow at those results!

-A

 

[lavatea]

Re: Description: heat-treatment process - Nigerian Tourmalin

Also, a complete aside! How does one get on your mailing list and to view your catalogue please? (sorry for the threadjack)

I'm not allowed to tell you how to get on my mailing list, though

Cheers,

Lisa
www.lisaelser.com

LD - I can tell you one possible way (I think the way I did it, though it's been a while). E-mail her.

 

[cellentani]

Re: Description: heat-treatment process - Nigerian Tourmalin

This has been one of the most interesting discussions in a long time!

Several times now, I've heard of tourmalines being sent to Brazil for heating and irradiation, including Nigerian material. Where then, are the irradiated tourmalines being sent once treatment is complete? Do any get returned to Nigeria? I find all of this to be rather frustrating, as most of the information, even on other gemology forums, seems to be third-hand information or hearsay.

Also, does anyone know what temperature is needed to heat tourmaline to achroic state? And will this temperature vary, depending on the color or origin of the tourmaline?

 

[lelser]

Re: Description: heat-treatment process - Nigerian Tourmalin

This has been one of the most interesting discussions in a long time!

...

Also, does anyone know what temperature is needed to heat tourmaline to achroic state? And will this temperature vary, depending on the color or origin of the tourmaline?

Tourmaline starts to burn over 750C. I've heated some to nearly that, held for an hour, and much of it goes clear, others look like tourmaline after the zombie apocolypse

 

[cellentani]

Re: Description: heat-treatment process - Nigerian Tourmalin

This has been one of the most interesting discussions in a long time!

...

Also, does anyone know what temperature is needed to heat tourmaline to achroic state? And will this temperature vary, depending on the color or origin of the tourmaline?

Tourmaline starts to burn over 750C. I've heated some to nearly that, held for an hour, and much of it goes clear, others look like tourmaline after the zombie apocolypse

Thanks Lisa, I appreciate all your input! I think I've seen one of your zombie tourmalines - it was indeed a most unholy color! By any chance, do you have better success heating pinks/reds to achroic better than blue/greens?

 

[lelser]

Re: Description: heat-treatment process - Nigerian Tourmalin

This has been one of the most interesting discussions in a long time!

...

Also, does anyone know what temperature is needed to heat tourmaline to achroic state? And will this temperature vary, depending on the color or origin of the tourmaline?

Tourmaline starts to burn over 750C. I've heated some to nearly that, held for an hour, and much of it goes clear, others look like tourmaline after the zombie apocolypse

Thanks Lisa, I appreciate all your input! I think I've seen one of your zombie tourmalines - it was indeed a most unholy color! By any chance, do you have better success heating pinks/reds to achroic better than blue/greens?

I don't intentionally heat them colourless. When that happens I consider it a terrible accident. The zombies NEVER go into inventory. They look burnt and lifeless and get thrown into the trash, where they are often carefully removed by our amazing cleaning woman

What I've found is that gems which get a reaction - whether positive or negative - will eventually sell. A colour you hate, someone else will love. Gems that get ignored will live in my inventory forever. When I question whether to heat something, it goes out to clients first to see if it's visible or invisible. After a while, if it never gets noticed I might as well heat it. I've got very little to lose if it cracks. Sometimes the better answer is recutting. I had a 2.4ct Tsavorite that was way too dark, and recut it to a 1.8 that is gorgeous. Better a smaller, pretty stone than a bigger lifeless one.

Cheers,

Lisa
www.lisaelser.com

 

[PrecisionGem]

Re: Description: heat-treatment process - Nigerian Tourmalin

Roger

Three questions if I may?

1. Was your heating process limited to red tourmaline please or did you experiment with other colours? I'm just wondering if all colours and species of tourmaline react in the same way i.e. would cuprian tourmaline do the same?
2. I have been told (by a vendor selling material) that the Nigerian or Mozambique "Rubellites" they were selling were irradiated - not simply heated. With that in mind, why would they go to this trouble if heating will produce a lighter gem please?
3. Have you personally seen any evidence of irradiated tourmaline?

Thanks in advance.

My experiments with Cuprian tourmaline from Mozambique is they change at 585 C. So this is a little hotter than the nice color change Roger got on the Nigerian stones. I had some very dark blue tourmaline from Nigeria, and have not had any success in heating them. I don't remember how high I went but it most likely around 800C or more and still no change.

 

[VapidLapid]

Re: Description: heat-treatment process - Nigerian Tourmalin

I have the paragon programmable oven but I dont have stones that need heating. Im not real likely to buy such stones. If I did, I still doubt that I would heat them. But then Im not a commercial entity trying to sell everything that comes into my hands. I have the oven left from a few (non jewelry) projects I was doing with slumped glass. Im not really interested in getting into heating stones anyway; already I go out of my way to avoid treated stones. I would, however, like to try using it to make billets of metals for mokume gane!!!

 

[VapidLapid]

Re: Description: heat-treatment process - Nigerian Tourmalin

Sorry just had horrible thought. What if: Treater puts copper into oven with tourmalines being heated. Copper diffuses like beryllium in sapphire. Instant paraiba?

 

[minousbijoux]

Re: Description: heat-treatment process - Nigerian Tourmalin

Not to agree with you Vapid (not that agreeing with you is bad, but because its a scary thought and I would much rather go on living in the land of denial), but I thought there was already an established method of diffusing something into tourmalines to make it appear paraiba-like...I remember seeing something showing microscopic growth tubes filled with color?

 

[Roger Dery]

Re: Description: heat-treatment process - Nigerian Tourmalin

Am back with a follow up as I've now performed some more heating.

Shown below: Heating to 500*C - a confirmed change, with lightening of tone, alteration of hue as well - this is the original stone at 6.54ct. I am showing it again here so you may have a reference from earlier.


Shown below: a different purple, but now pink Tourmaline at 6.91ct. Heating to 525*C - a significant change, with greater lightening of tone, serious alteration of hue


And here we have them both in the same photograph. Interesting that only 25*C will make that much difference in the look.


Thanks for all the questions - and I am truly hopeful that you may find this info useful.

 

[Colored Gemstone Nut]

Re: Description: heat-treatment process - Nigerian Tourmalin

I like the change after the first stage Roger. A slight loss of a re-cut to the pavillion would have done this stone more justice too. Its just my personal opinion, but I prefer the darker tone in the second photo. Really enjoying this thread and I hope you keep posting in similiar threads with different stones...

 

[Roger Dery]

Re: Description: heat-treatment process - Nigerian Tourmalin

I like the change after the first stage Roger. A slight loss of a re-cut to the pavillion would have done this stone more justice too. Its just my personal opinion, but I prefer the darker tone in the second photo. Really enjoying this thread and I hope you keep posting in similiar threads with different stones...

Hi Josh,
I have about 15 of these purplish/brownish/red Tourmalines to heat. They are all done in the same style -- and could all use a proper recut just as you have noted. However, they contracted with me to alter their color, and not to recut them. I believe they have all these stones sold "as-is" if I can get the color in-line with the pink they want as compared to being 'red' as they are.

 

[cellentani]

Re: Description: heat-treatment process - Nigerian Tourmalin

Roger, interesting topic, and great photos! How do the two stones look in incandescent light? I've experienced a lot of lighter pinks like your second stone going a bit brown and muddy, and wonder if there's any difference between the two colors.

 

[LD]

Re: Description: heat-treatment process - Nigerian Tourmalin

Roger, interesting topic, and great photos! How do the two stones look in incandescent light? I've experienced a lot of lighter pinks like your second stone going a bit brown and muddy, and wonder if there's any difference between the two colors.

That's a really interesting question! So, does it drive off the brown you may see in incandescent lighting! If it does then that would most definitely be a bonus!

 

[Roger Dery]

Re: Description: heat-treatment process - Nigerian Tourmalin

Roger, interesting topic, and great photos! How do the two stones look in incandescent light? I've experienced a lot of lighter pinks like your second stone going a bit brown and muddy, and wonder if there's any difference between the two colors.

That's a really interesting question! So, does it drive off the brown you may see in incandescent lighting! If it does then that would most definitely be a bonus!

Allow me some time, and by tomorrow I will set up an incandescent light to supply a corresponding photo with unheated, the 500*C and the 525*C so we can have a comparison.

From past experience though, they should still have a brownish modifier due to the color temperature of the light source.

 

[cellentani]

Re: Description: heat-treatment process - Nigerian Tourmalin

Roger, interesting topic, and great photos! How do the two stones look in incandescent light? I've experienced a lot of lighter pinks like your second stone going a bit brown and muddy, and wonder if there's any difference between the two colors.

That's a really interesting question! So, does it drive off the brown you may see in incandescent lighting! If it does then that would most definitely be a bonus!

Allow me some time, and by tomorrow I will set up an incandescent light to supply a corresponding photo with unheated, the 500*C and the 525*C so we can have a comparison.

From past experience though, they should still have a brownish modifier due to the color temperature of the light source.

That's awesome - thank you for indulging us, Roger. Can't wait to see the results!

 

[mastercutgems]

Re: Description: heat-treatment process - Nigerian Tourmalin

Really Great information Roger

I have always admired your work , talents, and knowledge... keep on keeping us informed...

Thank you ;

Most Respectfully;

Dana

 

[T L]

Re: Description: heat-treatment process - Nigerian Tourmalin

Where then, are the irradiated tourmalines being sent once treatment is complete? Do any get returned to Nigeria? I find all of this to be rather frustrating, as most of the information, even on other gemology forums, seems to be third-hand information or hearsay.

A lot of them go to Thailand I heard. I know, more heresay, but apparently they get this information for dealers in the know. I will never buy a tourmaline from anyone that cannot 100% verify their source, so that we know without a shadow of a doubt the material did not pass through Brazil. I will also not buy tourmaline from Thai dealers.

 

[colorluvr]

Re: Description: heat-treatment process - Nigerian Tourmalin

Another question, if you don't mind (for whomever can supply the answer). It's been stated that it may be difficult to tell if these stones have been heated by inspecting them "at home". Do you know if labs like AGL or perhaps Thai labs can tell if they have been heated or irradiated? (my apologies if this has already been answered). TIA for your respones.

 

[T L]

Re: Description: heat-treatment process - Nigerian Tourmalin

Another question, if you don't mind (for whomever can supply the answer). It's been stated that it may be difficult to tell if these stones have been heated by inspecting them "at home". Do you know if labs like AGL or perhaps Thai labs can tell if they have been heated or irradiated? (my apologies if this has already been answered). TIA for your respones.

Heating and irradiation of tourmaline is not detectable by any major gem lab, as far as I know.

 

[stylish1]

Re: Description: heat-treatment process - Nigerian Tourmalin

This information is from a book by Richard T. Liddicoat, Jr. A well known gemologist. I think that what he is saying is that when most any stone is heated or treated a good appraiser or gem identifier should be able to confirm the process has been done. This is for beryl, tourmaline, or spinel, etc.

 

[cellentani]

Re: Description: heat-treatment process - Nigerian Tourmalin

This information is from a book by Richard T. Liddicoat, Jr. A well known gemologist. I think that what he is saying is that when most any stone is heated or treated a good appraiser or gem identifier should be able to confirm the process has been done. This is for beryl, tourmaline, or spinel, etc.

Which edition is this excerpted from? This book has been around since the 1960's, and even then, Mr. Liddicoat makes a rather broad generalization. There definitely are treatments that are detectible, but I'm afraid not all of them are.

 

[Pandora II]

Re: Description: heat-treatment process - Nigerian Tourmalin

This information is from a book by Richard T. Liddicoat, Jr. A well known gemologist. I think that what he is saying is that when most any stone is heated or treated a good appraiser or gem identifier should be able to confirm the process has been done. This is for beryl, tourmaline, or spinel, etc.

Unfortunately this book by Liddicoat aka The Father of Gemmology, was published in 1947. Liddicoat himself died in 2002. Gem treatments have moved on significantly in the last 9 years let alone in the last 63.

My understanding is that irradiation of tourmaline cannot be detected in a laboratory. As far as heating goes, I would be interested to know how high a temperature it can be heated to get a good result. I imagine that inclusions will not be altered at the lower temperatures and so the chances of detection are low.

 

[stylish1]

Re: Description: heat-treatment process - Nigerian Tourmalin

12th edition, 1993, I understand he was around the 50's and 60's and was pretty well informed at the time. Im thinking with new teckno. being developed all the time that more and more treatments can be identified by a good appraiser who has been through several courses and with time under his/her belt. Tecnology is getting better and easier to find an answer to any whatever.

 

[Roger Dery]

Re: Description: heat-treatment process - Nigerian Tourmalin

Roger, interesting topic, and great photos! How do the two stones look in incandescent light? I've experienced a lot of lighter pinks like your second stone going a bit brown and muddy, and wonder if there's any difference between the two colors.

Cellentani,
So let's have a look under incandescent.....

These were all from the same batch, and generally their appearance before heating was somewhat interchangeable. On the left, heated to 525*C, center at 500*C, and on the right is unheated.

This photo was taken with 150 watt bulb at 18 inches. The Tourmalines are resting on a plate of clear glass, which is resting on a Photographer's 18% grey card. But as you can see, the incandescent lamp is 'washing out' all the depth of color in the stones as well as the surroundings. In the hand, there is a slight tan secondary to the stone on the left, almost giving it a 'peachy' hue. The center stone held its color fairly well, but the stone on the right has an obvious brownish modifier.

May be back later with further commentary.

 

[LD]

Re: Description: heat-treatment process - Nigerian Tourmalin

Thank you Roger. I see a very distinct brown cast to the gems but I appreciate that may be more to do with the photograph, lighting etc. However, this is pretty typical of what I generally expect from pink tourmalines and is why I personally, am not enamoured with them. So I guess it's safe to say that heating doesn't drive off the brown or stop them shifting in incandescent lighting.

 

[LD]

Re: Description: heat-treatment process - Nigerian Tourmalin

12th edition, 1993, I understand he was around the 50's and 60's and was pretty well informed at the time. Im thinking with new teckno. being developed all the time that more and more treatments can be identified by a good appraiser who has been through several courses and with time under his/her belt. Tecnology is getting better and easier to find an answer to any whatever.

I'm afraid that treatments are changing yearly, never mind through the decades! It is virtually impossible for labs to detect some treatments so appraisers without the use of very sophisticated equipment really can't identify whether a gem has/hasn't had a treatment with assurity.

 

[juliakaytaylor]

Re: Description: heat-treatment process - Nigerian Tourmalin

What an excellent thread! Thanks so much Roger for sharing your experiment/experience in such detail.

 

[Roger Dery]

Re: Description: heat-treatment process - Nigerian Tourmalin

Another question, if you don't mind (for whomever can supply the answer). It's been stated that it may be difficult to tell if these stones have been heated by inspecting them "at home". Do you know if labs like AGL or perhaps Thai labs can tell if they have been heated or irradiated? (my apologies if this has already been answered). TIA for your respones.

Hi colorluvr,
At the current state of forensic gemology, some of the researchers *may* have discovered a methodology to make quantifiable determinations regarding treatments to the Tourmaline family. But, they may choose to not add it to their menu of services until such time as they can feasibly handle the increased load they would endure.

I am not stating this is currently the case as I vigorously follow any discussions in the trade journals regarding this matter. When / if this comes to the attention of the gem trade, it would be significant news and would get serious coverage. It would be, as they say.... the talk of the town.

As you can imagine, keeping up with the latest treatment regimens is a top priority for the major gem laboratories. It is my understanding, that the majority of their research time is spent focused on Diamond, Corundum and Emerald. And in recent years there has been a forceful effort into the 'paraiba' category since it has been at the height of popularity.