Photoluminescence Spectra of Emeralds from Colombia, Afghanistan, and Zambia by Brian Thompson. See Research Below
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Fri Nov 24, 2017 5:21 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: Irradiated Topaz
PostPosted: Wed Jul 12, 2017 6:50 am 
Offline
New to the Forum or The Quiet Type

Joined: Thu Dec 08, 2016 5:15 am
Posts: 7
How we identify irradiated topaz.
Thank you


Top
 Profile  
Reply with quote  
 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 4:01 am 
Offline
Site Admin
User avatar

Joined: Fri May 12, 2006 11:24 am
Posts: 7468
Location: Rome, Italy
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...

_________________
GemmoRaman-532 - GemmoFTIR - GemmoSphere - EXA


Top
 Profile  
Reply with quote  
 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 12:33 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 18199
Location: San Francisco
May I presume the chromium peak would NOT be seen in blue topaz, natural or irradiated?


Top
 Profile  
Reply with quote  
 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 1:35 pm 
Offline
Site Admin
User avatar

Joined: Fri May 12, 2006 11:24 am
Posts: 7468
Location: Rome, Italy
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.....

_________________
GemmoRaman-532 - GemmoFTIR - GemmoSphere - EXA


Top
 Profile  
Reply with quote  
 Post subject: Re: Irradiated Topaz
PostPosted: Thu Jul 13, 2017 3:10 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 2603
Location: North Carolina
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: Irradiated Topaz
PostPosted: Fri Jul 14, 2017 3:23 am 
Offline
Site Admin
User avatar

Joined: Fri May 12, 2006 11:24 am
Posts: 7468
Location: Rome, Italy
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...

Quote:
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.

Quote:
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:

_________________
GemmoRaman-532 - GemmoFTIR - GemmoSphere - EXA


Top
 Profile  
Reply with quote  
 Post subject: Re: Irradiated Topaz
PostPosted: Fri Jul 14, 2017 5:40 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 2603
Location: North Carolina
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.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock