Gemstone treatments: discussion and questions

[PrecisionGem]

I actually have a question about how a tourmaline "should" be heated...
Experts, please help me~thank you!

I have a unheated copper bearing tourmaline that has some grey in it, so I'd like to heat it myself at home...
Is it possible and how? And is it safe to do so?

I don't want to end up with a colorless stone or a cracked stone

I'll check my notes tonight, but I think I have heat the Mozambique material to 585 C which is 1085 F. Your normal oven can't go this high. I ramp up by changing the temperature 100 degrees per hour, hold the stone for 1 hour, then allow the oven to cool by it's self which is about 12 hours. The stone is packed in a crucible and investment powder. There is always the chance for the stone to crack. I have had some stones that were flawless crack, and I've had some with inclusions that didn't.

Gene,
There seem to be two divided camps now two major issues. Do YOU believe there is a lot of tourmaline being treated right now?

I can't comment too much on cut stones, especially those being sold from the Thai sellers, since there is a lot of treatment going on in that part of the world. As far as rough goes that most cutters are buying on a smaller scale, then NO I don't think there is much treatment of tourmaline going on. Heating rough tourmaline is risky as quite a bit of the material will crack like crazy all over the place. I buy Nigerian rubellite from some small time dealers in Nigeria, as I suspect most of the other cutters known here are. These guys don't have the ability to nuke these stones, and it wouldn't make any sense that they would send them in small quantities to places that did, and then get them back. I would think any valuable stone, if you were going to heat it, would be done after cutting. I had a parcel of stones a few years back that belonged to a guy I know in Kenya. They were dark, brownish red, and he wanted me to try to heat them. I'd say 75% of them fractured in the heating, of those that didn't some became a nice pink, some almost colorless, and some very little change.

For those that would like to mess around with heating at home, I'd recommend zircons. Most zircon can be heated with just a candle flame. Hold the stone right above the flame with some tweezers, or put the stone in a test tube. The stones will change in just a few minutes and you can watch the color change. Heat them even longer and many will go colorless. Nigeria has pretty cheap "honey zircons" they are really brown and kind of ugly, but they can be heated to be colorless. They never seem to heat to any other decent color, so I don't really buy these, but I do have a few sitting around. As they heat up, they turn a nice orange, very bright. I used to have a few sitting on a coffee cup warming plate, and the heat from that would turn them orange, but after cooling they always go back to the ugly brown.

 

[VapidLapid]

200 C is the temperature you need to get the stones to and hold there. that's 392 F. your chicken will be over done at 185 F and may never reach 392. If you do get your chicken to an internal temperature of 392 it will burst into flame. May I suggest deep frying? That would give you a constant and even temperature. a more reliable method might involve getting one of these computer controlled countertop kilns that are used in glass forming. I have a small paragon kiln with programable computer that can ramp to 1800F at whatever rate I tell it, and program various soak cycles and an annealing cycle.
http://www.paragonweb.com/SC2.cfm

still it might be easier in the home to deep fry them

 

[Pandora II]

But I don't have a deep fat fryer!

Okay, I promise that if Chicken a la Kunzite doesn't work I will try a selection of other non-culinary methods!

 

[VapidLapid]

There is an additional problem posed by the chicken treatment technique. That is, any fractures and fissures in the stone would be likely to be filled with rendered chicken fat, also known as schmaltz. In the course of day to day wearing of stones so treated, there may emerge an unpleasant odor as the chicken turns rancid. A possibly more disturbing eventuality is the prospect of breeding salmonella. However this problem may also lead to a benefit. If one were to chose the deep fry method, one could tune the fracture filling effect of whatever oil one frys with, choosing an oil for its spectral tincture, or for its perfume, thus adding value to the stone and a more complex stimulation of the sensorium.

 

[Pandora II]

There is an additional problem posed by the chicken treatment technique. That is, any fractures and fissures in the stone would be likely to be filled with rendered chicken fat, also known as schmaltz. In the course of day to day wearing of stones so treated, there may emerge an unpleasant odor as the chicken turns rancid. A possibly more disturbing eventuality is the prospect of breeding salmonella. However this problem may also lead to a benefit. If one were to chose the deep fry method, one could tune the fracture filling effect of whatever oil one frys with, choosing an oil for its spectral tincture, or for its perfume, thus adding value to the stone and a more complex stimulation of the sensorium.

LOL! Not too worried as the stone is clean with no surface reaching fractures or inclusions. I don't wear 99% of my stones anyway - I like them in their boxes better.

I guess it could get expensive filling one's deep fryer with some oils - but I'm happy to see the results of your experiments in that arena!

 

[PrecisionGem]

Hey Vapid, that's the oven I have. If you look around you should be able to buy one for under $600 shipped. I have an old manual oven, still works well, but the programable system saves many trips up and down the stairs and staying up late at night to adjust the oven.

 

[cellentani]

I had the chance to go to a gem show today, and chatted with a faceter who had cut some large rubellites from Brazil and Nigeria. He claimed his rough was untreated, and I asked how he could tell. He said that even though rutile inclusions wouldn't be affected by the level of heat applied to tourmalines, liquid filled inclusions definitely would, and that's what to look for - intact, liquid inclusions. Does anyone know at what point a liquid inclusion will dissipate or rupture? Do any of the experts agree or disagree with this assessment?

 

[Treenbean]

I'm not an expert but it makes me wonder how common enhydro or dry enhydros exist in rubellite. I found this article that explains enhydros very well but doesn't have anything to do with melting or evaporation points.

http://www.rocksinmyheadtoo.com/Enhydros.htm

 

[cellentani]

I'm not an expert but it makes me wonder how common enhydro or dry enhydros exist in rubellite. I found this article that explains enhydros very well but doesn't have anything to do with melting or evaporation points.

http://www.rocksinmyheadtoo.com/Enhydros.htm

Are you asking how typical it is to see liquid inclusions in rubellite? I randomly checked 2 of my Nigerian rubellites, and they both had them. Oddly, mine have very few rutile, but his Brazilian rubellites had lots.

 

[Treenbean]

So you can see little water filled inclusions in the stone? If so thats pretty cool. I have only seen enhydro quartz.

 

[lelser]

I actually have a question about how a tourmaline "should" be heated...
Experts, please help me~thank you!

I have a unheated copper bearing tourmaline that has some grey in it, so I'd like to heat it myself at home...
Is it possible and how? And is it safe to do so?

I don't want to end up with a colorless stone or a cracked stone

I'll check my notes tonight, but I think I have heat the Mozambique material to 585 C which is 1085 F. Your normal oven can't go this high. I ramp up by changing the temperature 100 degrees per hour, hold the stone for 1 hour, then allow the oven to cool by it's self which is about 12 hours. The stone is packed in a crucible and investment powder. There is always the chance for the stone to crack. I have had some stones that were flawless crack, and I've had some with inclusions that didn't.

Gene - whilst you're looking at your notes, do you happen to know the temperature to heat Kunzite to please? I've got one that was once vibrant pink but is now almost colourless despite being in my safe and not exposed to sunlight ever I was very tempted to put it inside a chicken and cook in the oven but looking at your temperature guide for Tourmaline, I'm guessing that wouldn't work?

This is hysterically funny!! The thought of you cooking your kunzite inside a chicken in the oven!!! Hahahahaha!

I have an article on heating Tourmaline coming out in May or June in Lapidary Journal. As Gene said, it's quite a bit of trial and error. You can make educated guesses with material from the same mine and same find but beyond that it's tricky. We chopped up some representative Tourmalines and sent them to their deaths so we could compare results at different temperatures.

Having the right oven matters. Thermal shock is death (hence the whole "pack it in investment" thing) and a good oven not only ramps the heat slowly, but doesn't allow drafts or rapid cooling.

Cheers,

Lisa
www.lisaelser.com

 

[VapidLapid]

Today a friend who designs jewelry for a big famous gaudy house that I would rather not name but you all know told me about how he heat treats spinels. He takes the finished cut stone with pliers and holds it directly in the flame of a oil burning lamp. No ramping up, no annealing down, no soak time. He claims it takes about 30 seconds for a pale pink tanzanian spinel to turn deeply bright pink. Now I have my doubts about the process, though I have no reason to think he would lie. And I did rather innocently say, but I thought spinel didn't respond to any known treatments? And I asked him if there was any other effect or telltale signs like dissolved rutile or ruptured enhydros or cloudy bursts and he said no. Maybe he wasnt expecting me to know so much about the subject. While Im sure there are some or many who are trying to successfully heat spinels, I have doubts that 30 seconds in the flame of an oil lamp would do the trick.

Anyone have experience, heresay or opinions on the subject?

 

[lelser]

As the owner of lots of pale pink spinel, I'll try this when I get home on some smaller rough and post the results. I've never heard of this working, but can risk a rough stone on the experiment.

Lisa
www.lisaelser.com

 

[chrono]

I have not heard of such easy heating of spinels to improve colour. One would think that GIA would have observed any colour improvement in low temperature heating while conducting their heating experiments with spinels.
http://www.gia.edu/research-resources/news-from-research/Heated%20spinel%20Identification%20at%20April%2002%202009.pdf

 

[VapidLapid]

well this is my test I give you all so you won't need to try this at home. First the stone on a white background.

Second the stone placed in the mouth of a graphite crucible that I hacked out of a block of graphite



Add fire!



more fire

 

[VapidLapid]

And More fire



Still more fire. You would even say it glows!



The result



To quote Yukon Cornelius, "Nuthin'"

 

[VapidLapid]

Thank you Chrono for that wonderful and informative link.

 

[T L]

VL,
Glad you didn't torch the snowman too. He still looks happy.

 

[chrono]

VL,
Thanks for the home-made test. I do have to admit the cookies are what caught my eyes first until the spinel started to glow. Did the clarity of the spinel improve?

 

[VapidLapid]

Chrono, I am a sloppy scientist. In my rush to torch the stone I did not bother to make an assessment of its clarity. The stone came from the jar of spinels left over after picking out the best for a project. But even that is inconclusive. Now that you've asked I have louped the heated stone and while I dont have a before assessment to compare with I can say the stone is clean(!) I see no inclusions, and the feather fracture (quite tiny and not deep) that was there is still there and no deeper. This torch is supposed to reach 1500 C but I have never been able to attain that heat when trying to melt tiny amounts of silver. Just saying that to give you some indication of the temperature. The total time in the flame was 60 seconds
These pics are just now after heating trying to show clarity:

 

[minousbijoux]

Yes, but how did the cookies taste?!!!

 

[VapidLapid]

I do think it odd though, that the GIA abstract says,"...these experiments showed that the spinels did not improve in appearance but rather they became darker..."
This seems to imply that only a lightening of color would be an improvement. But what of the intensifying of color from a natural but anemic pink to a rich mahengy pink? This is what my friend claimed he was doing. The GIA abstract showed pretty nice spinel to begin with that were changed to darker and then were lesser in appearance after treatment. It does show an effect. There was a response, a change in the color.

On another note, it seems with all the chicken and pies and cookies that we are the pillsbury research kitchens of the gem world. Someone should fund our amateur, parallel research.

 

[minousbijoux]

So perhaps next up is to put a spinel in a chicken...

On a more serious note, I wonder if the duration of heat makes a difference, i.e. if the heat is low as in cooking the chicken, but for many hours as opposed to the relatively short duration required of a chicken? Since Pandora's experiment was successful, it makes me wonder if longer would have a more pronounced shift in color...

 

[VapidLapid]

I would like to see someone put a chicken in a spinel