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 Post subject: Irradiated Topaz
PostPosted: Wed Jul 12, 2017 6:50 am 
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How we identify irradiated topaz.
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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 4:01 am 
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basically you can't. However, you can try the hard way which works for some "imperial" topaz: put the stone under a ventilated 100 w bulb at say 15 cm far and leave it there for 24 hours or more. Usually, if the material is irradiated it should fade at some extent (depending on the stability of color centers). Of course that is a partially "destructive" test so you really need to consider that in advance. OTOH if you have a Raman/PL spectrometer at hand you could get a scan and evaluate the presence/extent of the PL chromium peak at 684 nm. IF you are dealing with a nicely saturated stone and you can see both the chromium PL peak AND the Raman fingerprint there's for sure something suspicious. Raman signal is VEEEERY weak comparing to PL reactions so, having them both visible in the same scan means the presence of chromium is very weak hence the nice color should be generated by another factor....... :wink: :wink: :wink:
my 2 cents only...

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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 12:33 pm 
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May I presume the chromium peak would NOT be seen in blue topaz, natural or irradiated?


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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 1:35 pm 
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Barbra Voltaire wrote:
May I presume the chromium peak would NOT be seen in blue topaz, natural or irradiated?


of course not, i was specifically referring to the claimed to be "imperial" topaz which VERY often are irradiated and sold as the real deal....the blue topaz are not a major gemological issue, i mean, i don't know how many gemologists have doubt about the origin of their color.....

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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 3:10 pm 
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Do you mean Brazilian Cr-bearing material or the stuff from Katlang? You can certainly bump the color up on either with irradiation, but why some portion of the color is stable and some isn't is a true mystery. It's not just a matter of chromium content I don't think, there's some other special sauce. I had never heard of the raman method, I will have to try that.

As a side-note I actually have seen a blue topaz with reported chromium content which I found very strange! It's from the GIA's Gem Project, a large blue topaz from Zimbabwe (the renowned locale for natural intense blues, before irradiation ruined that):
Image
I have no idea what the heck is going on with this.

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 Post subject: Re: Irradiated Topaz
PostPosted: Fri Jul 14, 2017 3:23 am 
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Stephen Challener wrote:
Do you mean Brazilian Cr-bearing material or the stuff from Katlang?


I mean what is marketed as Brazilian. I know for sure some of that stuff is irradiated and fades more or less quickly...

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You can certainly bump the color up on either with irradiation, but why some portion of the color is stable and some isn't is a true mystery. It's not just a matter of chromium content I don't think, there's some other special sauce.


Yes, probable, but the correlation between color saturation and PL peak extent is pretty consistent in my tests.

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I had never heard of the raman method, I will have to try that.


that is PL, not Raman. you really need to have a visible laser system to get it. :wink:

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 Post subject: Re: Irradiated Topaz
PostPosted: Fri Jul 14, 2017 5:40 pm 
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Fair enough. I will still have to take some time to see what I can see with raman scans--goodness knows I have enough test subjects of various sorts lying around.
How often do you see irradiated 'imperial' topaz? I tried irradiating two golden sub-imperial stones and was really impressed with the rich, glowing red-orange color they took on (and with how quickly they faded back to their original coloration). I also read once that a lot of irradiated 'imperial' was being sold in Brazil back in the 80s, to the point that a lot of dealers took to taping topaz to their windows to show they were stable. In spite of that this specific treatment almost never seems to be discussed.

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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Aug 19, 2021 9:25 am 
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True Blue Topaz seems to be every bit as elusive as that roll of toilet paper (or paper towels) during the middle of a pandemic! As one of the rarest natural colors of Topaz, it's almost never seen in the commercial market. The Blue Topaz that we know is an irradiated form of the most common topaz of all-White Topaz. Natural Blue Topaz is truly a collectible gem and mimics the color of Aquamarine. However, most Natural Blue Topaz has such poor color saturation, that it ultimately ends up in the nuclear reactor alongside White Topaz to get a little "atomic enhancement".

Today, most of the irradiated Blue Topaz supply comes from the Thai Government facility in Bangkok. They have a multi-use facility that irradiates many other gemstone types, in addition to perishable food items.

Radiation treatment is permanent, so there is no issue with color fading. In addition, prior to irradiation, most White Topaz is heat-treated first, to remove any color impurities. So you'll have a stone that is clean and with an amazing depth of color. Ultimately, any shade of Blue Topaz is safe to wear, and its hardness provides an extremely durable gemstone to wear every day.


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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Aug 19, 2021 12:02 pm 
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navneetagarwal wrote:
Ultimately, any shade of Blue Topaz is safe to wear, and its hardness provides an extremely durable gemstone to wear every day.
I disagree, where as the topaz treated to the shades of London Blue and the
Swiss colors can still be quite "hot" for some time after treatment. Where certification is required before use in the jewelry industry. Although many have found means to bypass a certification.

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 Post subject: Re: Irradiated Topaz
PostPosted: Thu Aug 19, 2021 12:32 pm 
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Natural blue topaz isn't too hard to source. I have a bunch from Nigeria with lovely aqua-like color.


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