Have they "modified" the treatment for Tanzanite?

[RedSpinel]

When I first started seeing lots of tanzanite being sold on the internet, jewelry stores, TV, etc. it was about 9 years ago. back then Tanzanite seemed to come in 3 main color grades. The best was that pure, royal blue with no noticeable violet tint. Obviously Tanzanite is trichroic, so you will get flashes of other colors like red occasionally, but the primary color in the top grade tanz. was royal blue.

The next level down was blue-violet. It would be mostly blue, but with some violet tint to it. The lowest quality tanz. was just pure violet. It had no blue, only violet. It was always the cheaper Tanzanite material. There would be some fluctuation within these categories of how blue or violet was visible, but the colors were pretty standard.

But in the last few years, I'm now seeing lower to mid priced Tanz that is mostly blue, but its not the same blue you'd see 8-9 years ago. Its a different shade of blue altogether. There seems to be more of this and less pure violet stones. I know that Tanzanite has been treated for almost as long as its been available, but I'm wondering if they have come up with new or modified treatment that is resulting in these newer colors, and resulting in the lack of the pure violet stones. Maybe they can now take the violet rough, treat or heat it in a "revised" manner, and turn it blue-ish instead.

Also, the top grade. pure royal blue Tanzanite seems to be less common than before, and some dealers are selling the blue-violet, mid grade stones and calling them top grade, and even going as far as to tell their customers that top grade Tanzanite is SUPPOSED to have obvious violet in it, and not pure royal blue! Others will tell you its pure blue, even while you're looking at a stone that is 30-50% violet!

I know there used to be 4 different mine blocks that the rough came out of, and supposedly "D" block was best, and "C" block was where the violet stuff came from, at least thats what I read years ago.

 

[chrono]

It is entirely possible that a new treatment method has been discovered and undisclosed. I'll have to check other forums to read up on the lastest tanzanite treatment news.

 

[LD]

No. Nothing to do with treatment. What you're describing is down to quality only. D block still produces the best BUT they are now mining deeper under D block and there are some exquisite stones being mined.

Treatment for tanzanite is mostly limited to heating but is considered normal ie think of oiling for emeralds. A few years ago there was some filling and dyeing but I hadn't heard of any being around recently.

 

[Lee Little]

I would say the same thing, no new treatments that effect color, just an adjustment on what colors are available. Green and green blue is also now being called Tanzanite but that is simply a stretch of the definition, not a treatment (green Zoisite just didn't sell) best regards, Lee

 

[Swala Gem Traders]

Hi All (haven't been on the forum for a while ...),

A few things I would say about tanzanite:
. there are no official grading systems. If I was to establish one, RedSpinel, I would have a scale of at least 10 or 15 different grades (all linked to tones)
. within the trade, purple in tanzanite has nothing to do with grade but is a matter of personal preference. In other words, if a tanzanite is dark, whether or not it has purple, will be consider as a better "color'
. most tanzanites exhibit more purple under yellow lighting conditions. The same gem will appear more blue under white lights
. until a few years ago, the only 'treatment' was heating which would bring out the blue color
. smaller gems, lighter gems, have been found to be enhanced with cobalt coating (treatment discovered at least 4 years ago)
. to the best of my knowledge, nothing new since then
. block D is not a guarantee of quality and top tanzanites are also found in other blocks

I hope that helps.

 

[ChrisA222]

Swala...I have in my collection, quite a few of what was called, by the vendor and seemingly in the trade, as "unheated" Tanzanite. These all have some combination of purple, blue, and green. The good ones look exactly that...nicely saturated, different colors coming off different axis. Some of the lesser quality ones look grey. Are these stones really "unheated" or is that just a marketing term?

I read somewhere that nearly all Tanzanite has been heated...but if so, why am I seeing three colors, when from what I've always understood, Tanzanite loses its third color upon heating. So, which is it...are most Tanzanites heated, and the ones that still have green just considered "B" grade stones? Or are they actually unheated. If they were unheated, why weren't they heated to get the more popular deeper blue/purple color?

Just something I've always wondered about when it comes to Tanzanite...

These are a couple of examples of 'unheated' Tanzanite that I own, from very unsaturated to nicely saturated...

 

[PrecisionGem]

All tanzanite will show 3 colors, depending on the axis you view the stone. Sometimes the colors are a subtile difference however and you may think you only see 2 colors. Here is where a good dichroscope comes in (I recommend the Gemology Pro). Most tanzanite is heated. The unheated stone has kind of a root beer color, and can have a gray axis, green, blue, purple, yellow. There are natural blue stones that are not heated. I have found that these natural blue stones do show a stronger 3 colors than heated stones do. I'm sure as with anything else there are exceptions, but this has been my observation.

 

[chrono]

I am sure there are unheated tanzanite out there, but that would be uncommon. There is always the possibility that Mother Nature heated it up enough so that we don't have to when they are dug up. As far as I know, tanzanite will always show different colours on all 3 axis, no matter the treatment. Perhaps the colours look too similar to your eyes to make out the difference?

 

[ChrisA222]

Chrono, not going by "my eyes", lol...going by wherever I was taught that. I didn't make it up or discover it on my own, I wish I could tell you where I learned that Tanz loses its third color when heated-I was told the third color turns into the primary or secondary so you only see two colors. Since I learned much about Tanzanite as a newbie from JTV, I can now laugh about it...Thanks for clarifying.

So all the 'unheated' Tanzanite out there being sold is a marketing thing? To help sell the stones that have the green as an obvious color? Interesting. Those three stones, ranging from grey to blue/purple/green were all purchased by me and sold to me as examples of 'unheated' Tanzanite. lol

 

[LD]

Chrissa - there is a school of thought that says tanzanite can be more dichroic rather than trichroic if heated. I peesonally dont velieve fhis based on my experience.

Tanzanite is the marketing term for blue zoisite. All other colours are technically zoisite not tanzanite but are commonly sold as unheated tanzanite which is technically incorrect.

Tanzanite (blue) comes out of the ground blue, brown, grey etc and most is heated to give it a blue or purple colour.

Unheated zoisite comes out of the ground and can be orange, pink, green, yellow. They do not always have a grey mask. They can be quite beautiful. I've posted mine before so if you search under my name you should be able to see photos of all colours I've mentioned.

 

[chrono]

I concur with LD. The true name for the gem type is zeosite. The blue variety has been given the marketing name of Tanzanite and are usually heated. If the stone is of any other hue (whether heated or not), it is classified as a zeosite.

 

[VAgemguy]

I've seen fancy unheated zoisite (tanzanite) in lots of different colors, including pink, purple, peach, copper, green, blue. Many have other colors visible also as has been mentioned previously. I believe that JTV as coined the term "ocean tanzanite" for the blue/green shades and has done a lot of marketing around them lately. A couple of your examples look like ocean tanzanite to me. I talked to the guys at Prima about fancy zoisite in the past and they said that there are several reasons that fancy stones are not heated -- sometimes they have inclusions that would cause the stone to explode when heated , other times (as with the blue/green) the fancy hue might be more marketable/valuable than it would be if heated (e.g., a pretty blue/green stone may fetch more than a low grade blue/violet). However, since 99.9% of the consumers expect tanzanite to be purple, most stones get heated as standard practice. Like anything else though, fine examples of fancy zoisite can be really beautiful, unique, and interesting.

 

[ChrisA222]

VA, that is what Im saying...so, you just confused me more than anything else. So are those "ocean" Tanzanites like in my second/third picture, are those heated or not. Are you saying they are unheated, like as advertised, because if heated they would be low-grade violet, or are you saying they are heated, yet retained the strong third color (the green).

That is the question I am trying to ask! Are these blue green Ocean Tanzanites technically "unheated" or is that just the name they are given by the sellers to designate that they have the green color on one of the axis.

 

[chrono]

It is likely that your "ocean tanzanites" are unheated, but they really should be called zeosite because they are not blue / violet. The name is just something to make the stone sound special, and by that token, more saleable.

 

[LD]

VA, that is what Im saying...so, you just confused me more than anything else. So are those "ocean" Tanzanites like in my second/third picture, are those heated or not. Are you saying they are unheated, like as advertised, because if heated they would be low-grade violet, or are you saying they are heated, yet retained the strong third color (the green).

That is the question I am trying to ask! Are these blue green Ocean Tanzanites technically "unheated" or is that just the name they are given by the sellers to designate that they have the green color on one of the axis.

If you see green OR a green/blue mix of Tanzanite (really should be called Zoisite) it is NORMALLY unheated. However, some do retain a smidge of green even after heating. So it's incredibly difficult to answer you with 100% accuracy BUT if you see green, it's safer to assume unheated.

You cannot predict what colour it would be if heated - so forget about low grade violet etc.

 

[Swala Gem Traders]

Chrisa,

The zoisites you are showing here certainly seem unheated (especially the first two).

Basically, when heated, the colors of the zoisites tend to blend into blue. The trichroism is less visible.

The only reason why people heat tanzanite - and yes, an important percentage (personal estimates > 99%) of the zoisistes on the market have been heated - is to sell a gem with a more sought after color. Therefore, if a zoisite is not heated, it is because it is either naturally of a nice blue or because the odd color as unheated is more interesting than if it was heated.
As unheated, you will see all these fancy colors which, for most part, are not attractive. A few years ago, a lot of brokers and miners in Arusha were trying to sell what they called "combat" colored zoisites. These gems were green but were not attractive. Eventually they understood how to decipher green and green

On rare occasions will you see an interesting green, purple, yellow, orange or pink zoisite. In which case, it is better not to heat the gem.

 

[ChrisA222]

Swala, great info...loving it.

Can you take a stab at, using the first two pictures I posted, why these two stones were not heated? The first one is grey....by anyones defintion. True, some may like gray, as the stone is very brilliant, but most would not want a grey gemstone. The second one, you can make a slightly better case for it, it is interesting, but again, greyish. Why wouldnt these two be heated? Do the gem heaters know which stones will just not improve if heated? So, in other words, that grey stone in the first pic, what would happen to it if it were to be heated?

Maybe these questions cannot be answered, but I still wanted to ask as I am trying to learn as much as I can. At least I now know that all tanz has the three colors if looked at closely, and that these stones ive posted are most likely unheated as was sold to me. I understand others issue with calling them Tanzanite, but that wasnt really what I needed clarified. A name is a name is a name. I am just primarily interested in if the gem is heated, what happens if its heated, why it wasnt heated to try to improve it,etc etc.

Thanks all!

 

[RedSpinel]

VA, that is what Im saying...so, you just confused me more than anything else. So are those "ocean" Tanzanites like in my second/third picture, are those heated or not. Are you saying they are unheated, like as advertised, because if heated they would be low-grade violet, or are you saying they are heated, yet retained the strong third color (the green).

That is the question I am trying to ask! Are these blue green Ocean Tanzanites technically "unheated" or is that just the name they are given by the sellers to designate that they have the green color on one of the axis.

The stones in the bottom 2 pictures are an example of what I was talking about when I typed the OP. Back about 10 years ago, and maybe as recently as 8 years ago, I dont ever remember seeing those colors. I dont remember there being a light-ish blue or blue green. It was either royal blue, blue-violet, or violet(or the so called green tanzanite). I dont know if that means they were heating all the light blue-ish rough to make it violet, or whether it started out another color, then was heated to become light-blue or blue green. It doesnt make sense to me that anyone would take rough that was already mostly blue(the most sought after color), then heat it to make it into a less sought after color like violet. I know that many people thought that violet was the good color, but those violet stones were always sold to those people for much less money, and any stone that was mostly blue wouldve brought more money, so why do it?

 

[PrecisionGem]

Chrisa, I would say all three stones you posted are not heated. The first two I doubt would do much with heating. My experience heating stones of that color have not been too favorable, maybe a small color shift toward purple could be achieved. The third stone I think it too interesting to heat, I like it the way it is.

I was told a few years back from Steve at New Era Gems, who has heated a lot of tanzanite, that stones with a green axis don't heat well. So I have alway avoided buying these, and have no experience heating them. It's always a gamble when you heat a stone. The color of the unheated stone does give you an indication of the finished color, as does the tone of the rough. But bad things can happen in the oven. I have seen totally clean stones fracture, and I have seen slightly included stone fracture like crazy, and also come out of the oven just as they went in.

When ever I have heated tanzanite, after heating the distinction of the 3 colors has been less than it was in the rough, and less than what I see in natural blue stones.

In Africa and Tucson when buying rough, I have always seen tanzanite that wasn't blue referred to as fancy tanzanite. I don't think anyone does this to try to deceive or think the name has any marketing value. Fancy colored tanzanite in pinks, greens, yellows sell for much higher prices than heated blue tanzanite does. There are collectors who love these stones, and pay a high price for them since they are so much more rare.

 

[PrecisionGem]

VA, that is what Im saying...so, you just confused me more than anything else. So are those "ocean" Tanzanites like in my second/third picture, are those heated or not. Are you saying they are unheated, like as advertised, because if heated they would be low-grade violet, or are you saying they are heated, yet retained the strong third color (the green).

That is the question I am trying to ask! Are these blue green Ocean Tanzanites technically "unheated" or is that just the name they are given by the sellers to designate that they have the green color on one of the axis.

The stones in the bottom 2 pictures are an example of what I was talking about when I typed the OP. Back about 10 years ago, and maybe as recently as 8 years ago, I dont ever remember seeing those colors. I dont remember there being a light-ish blue or blue green. It was either royal blue, blue-violet, or violet(or the so called green tanzanite). I dont know if that means they were heating all the light blue-ish rough to make it violet, or whether it started out another color, then was heated to become light-blue or blue green. It doesnt make sense to me that anyone would take rough that was already mostly blue(the most sought after color), then heat it to make it into a less sought after color like violet. I know that many people thought that violet was the good color, but those violet stones were always sold to those people for much less money, and any stone that was mostly blue wouldve brought more money, so why do it?

Normally heated a natural blue stone has very little effect on it. If it does it will be only to increase the blue saturation, not make it go purple. Heating a natural blue will NOT make it go purple or violet.

Most heated or natural blue tanzanite will have one axis that is blue, and another that is purple. If you cut it one direction you will a stone with more blue, cut it the other way and you will get a stone more purple. In the USA, people tend to like the blue stones better, but this isn't true all over the world, some place prefer the purple.

Heating doesn't guarantee any finished color. Certain rough unheated colors heat to a very nice blue, some not so nice, it all depends on the rough.

 

[LD]

If you look at the ones below, and if you didn't know they were zoisites, you would be forgiven at guessing completely different gemstones! When they look this different to what people refer to as Tanzanite, you can understand why they can command prices the same and sometimes higher than their heated counterparts. However, they don't appeal to a huge market which is probably why most get heated. However, even if they were all heated, there's no guarantee of a lovely colour after - which is why I suspect some are left au natural!

I love the pinks, the very saturated greens and I have an orange that I can't find a photo of that I really do like but they are an acquired taste!

The green/blue ones being sold by shopping channels are given fancy marketing names (in the UK they called them Chameleon tanzanites) and they charge a premium for them but in all honesty and in my opinion, they probably should be sold for less than normal good quality blue tanzanite.

 

[RedSpinel]

If you look at the ones below, and if you didn't know they were zoisites, you would be forgiven at guessing completely different gemstones! When they look this different to what people refer to as Tanzanite, you can understand why they can command prices the same and sometimes higher than their heated counterparts. However, they don't appeal to a huge market which is probably why most get heated. However, even if they were all heated, there's no guarantee of a lovely colour after - which is why I suspect some are left au natural!

I love the pinks, the very saturated greens and I have an orange that I can't find a photo of that I really do like but they are an acquired taste!

The green/blue ones being sold by shopping channels are given fancy marketing names (in the UK they called them Chameleon tanzanites) and they charge a premium for them but in all honesty and in my opinion, they probably should be sold for less than normal good quality blue tanzanite.

They used to sell the "green Tanzanite" on GSN back in the day, and they'd charge less for it than for the pure blue stones, but more than for the violet stones. So it was mid priced. It seemed to be around $100- $200 per ct back then depending on the seller, etc. Thats while the best royal blue material was going for $500/ct then $700/ct, and the violet was around $75- $100/ct as I recall.

 

[Arkteia]

Swala,

When you say "cobalt coating" you mean, coating, not irradiation? I found reference to AGTA page re. coating, but the page does not exist any longer.

Also, if the coloring element is vanadium, one should be able to distinguish between coated and uncoated tanzanites by spectroscopy, right? (I.e. there would be no cobalt lines on spectra of uncoated stones).

Also, does one see less trichroism in cobalt-coated stones?

(There is absolutely no hidden meaning in my questions, just trying to learn.)

 

[mastercutgems]

Gene, Swala... Thanks for your input as it is how I was taught many years ago as I have been heating and cutting "tanzanite" for about 17 years and got a lot of my Zoisite/Tanzanite from Hilmar Bosch and you never knew what you were going to get as they stopped heating it before cutting as if it had a flaw it could pop and back then their method for heating was a little on the primitive side; like wrapping it in charcoal/foil and putting it in the fire...

But we would get bi-colored terminated crystals in blue and green, purple and green, purple and straw color, brown, orange and pink, etc. and Gene is right sometimes it was best to leave the color alone and not heat it as sometimes it would go butt-ugly with you... So you learn to orient for the best color; cut it and then if you do not like it; heat it to about 850 to 950 F and let it hold for a couple of hours and cool on it's on very slowly and usually if you did not have any flaws in the gem it would come out fine; although i have known some to heat then if they did not like it heat it again up to 3 times; but I was always afraid of them as that may set up some really serious crystalline structure issues and well maybe unstable???

But I too have only heard of the smaller gems that were the lilac color being coated and I think there was an immersion fluid you could use to test for that; i will have to check my old notes...

But Swala and Gene both have dealt with a lot of tanzanites also and can further the topic of heating as i truly do not claim to be an expert on heating them ... But still do it as it is like Christmas as you never really know until you take away the charcoal insulator and hope and pray it did not pop...

Most respectfully;

Dana Reynolds
ASG Certified Supreme Master gem Cutter #96cge42

 

[PrecisionGem]

If you look at the ones below, and if you didn't know they were zoisites, you would be forgiven at guessing completely different gemstones! When they look this different to what people refer to as Tanzanite, you can understand why they can command prices the same and sometimes higher than their heated counterparts. However, they don't appeal to a huge market which is probably why most get heated. However, even if they were all heated, there's no guarantee of a lovely colour after - which is why I suspect some are left au natural!

I love the pinks, the very saturated greens and I have an orange that I can't find a photo of that I really do like but they are an acquired taste!

The green/blue ones being sold by shopping channels are given fancy marketing names (in the UK they called them Chameleon tanzanites) and they charge a premium for them but in all honesty and in my opinion, they probably should be sold for less than normal good quality blue tanzanite.

LD those are nice colors. Very rare to find the nice greens. None of them in the picture would heat to blue. The two bottom stones would change to maybe a light blue/purple color. It would be crazy to heat the others as the value would only go down, and the color wouldn't go to a blue anyways.

 

[LD]

Thank you Gene.

I may be wrong Eric but I think there was an influx of coated smaller Tanzanites about 5-8 years ago but I haven't heard of any recently. Of course, as I'm not buying Tanzanite, it could be littered on the market and I wouldn't know. i do recall however that if you scratched the stone the coating would come off.

 

[RedSpinel]

VA, that is what Im saying...so, you just confused me more than anything else. So are those "ocean" Tanzanites like in my second/third picture, are those heated or not. Are you saying they are unheated, like as advertised, because if heated they would be low-grade violet, or are you saying they are heated, yet retained the strong third color (the green).

That is the question I am trying to ask! Are these blue green Ocean Tanzanites technically "unheated" or is that just the name they are given by the sellers to designate that they have the green color on one of the axis.

The stones in the bottom 2 pictures are an example of what I was talking about when I typed the OP. Back about 10 years ago, and maybe as recently as 8 years ago, I dont ever remember seeing those colors. I dont remember there being a light-ish blue or blue green. It was either royal blue, blue-violet, or violet(or the so called green tanzanite). I dont know if that means they were heating all the light blue-ish rough to make it violet, or whether it started out another color, then was heated to become light-blue or blue green. It doesnt make sense to me that anyone would take rough that was already mostly blue(the most sought after color), then heat it to make it into a less sought after color like violet. I know that many people thought that violet was the good color, but those violet stones were always sold to those people for much less money, and any stone that was mostly blue wouldve brought more money, so why do it?

Normally heated a natural blue stone has very little effect on it. If it does it will be only to increase the blue saturation, not make it go purple. Heating a natural blue will NOT make it go purple or violet.

Most heated or natural blue tanzanite will have one axis that is blue, and another that is purple. If you cut it one direction you will a stone with more blue, cut it the other way and you will get a stone more purple. In the USA, people tend to like the blue stones better, but this isn't true all over the world, some place prefer the purple.

Heating doesn't guarantee any finished color. Certain rough unheated colors heat to a very nice blue, some not so nice, it all depends on the rough.

Lets say you have Tanzanite rough, from the same parcel, from the same area in the mine, mined the same day, the same color, and you heated it. Would it likely all come out the same color, or is it so variable that you never know what you are going to get?

 

[PrecisionGem]

Redspinel, given those parameters then I would say the heated color would be pretty consistent. However, the orientation and cut could alter the the color the stone show predominantly. You could still cut them to be more toward the blue side or more toward the violet side.

 

[Swala Gem Traders]

Sorry for my late replies...

Arkteia:
Yes, I was referring to cobalt coating.
Heated or with cobalt coating, trichroism appears less than with a piece of unheated rough.
Not sure how the labs determine the cobalt coating.

LD:
I'm not sure to what extent the coating is used. It's mainly done on smaller gems as the smaller tanzanites usually lack the depth to be of a high tone.

RedSpinel:
The color/tone depends on different variables.
Take the example of one piece of rough. It may be sliced to cut a few gems. If it is thinner on one side, the cut stone from the thinner area may be paler. Also, it also depends on the orientation of the stones you cut. You may position the table (main facet) differently from one gem to the other. The axis used for the table may not be the same and the end result will again be different.