January 24 Through February 4—TUCSON, ARIZONA: Annual show
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Thu Mar 28, 2024 7:12 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 11 posts ] 
Author Message
 Post subject: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 5:29 pm 
Offline
Valued Contributor

Joined: Tue Jan 02, 2018 11:12 pm
Posts: 206
If I heat treat a Topaz and it start to turn blue,
can I be certain at that point that The material was Irradiated?
Thanks.


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 5:55 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
No, if you have a natural topaz that has brown and blue heating will remove the brown mask and improve color the same as with artificially irradiated material. (I am not convinced blue coloration actually increases in this process, though it's hard to get firm data.)

_________________
Rough and cut classic and exotic synthetic gems:https://store.turtleshoard.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 6:18 pm 
Offline
Valued Contributor

Joined: Tue Jan 02, 2018 11:12 pm
Posts: 206
Stephen Challener wrote:
No, if you have a natural topaz that has brown and blue heating will remove the brown mask and improve color the same as with artificially irradiated material. (I am not convinced blue coloration actually increases in this process, though it's hard to get firm data.)


Thanks Stephen.
I experimented with a faded/very light brown color material from mexico, it seems that if I lightly heat it for a few seconds,the color becomes stronger ,(not sure how stable it is over time,need to test more) but it's only get stronger up to a point that If I continue to heat, it will just turn pale again to the same tone it was before heating, but blue.

so basically you're saying that regardless if it's Irradiated or not, I just removed the brown..

Thanks!


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 8:09 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
Having irradiated and heat treated literally millions of carats of blue topaz this is what I came to believe.

Natural brown topaz will fade. More heat more fade all the way to colorless. Natural brown will never turn blue, it will only show blue if there was blue already in the stone.

Irradiated Topaz come out of the Linac with both brown and blue. The blue doesn't turn into blue, it masks it. The brown burns off at a lower temperature leaving the blue. But with enough heat you can also burn off the blue. Some oif the blue can fade so you must anneal the blue to get rid of the unstable color so it won't fade on your customers.

In order to know the way to treat the stones you must know what the source of the irradiation was Linear Accelerator (Electron Beam), Gamma Tank, Neutron Tank, or some combination of the above.

I must admit I never tried heat treating with a torch. Always in a temperature controlled oven.


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 9:20 pm 
Offline
Valued Contributor

Joined: Tue Jan 02, 2018 11:12 pm
Posts: 206
1bwana1 wrote:
Having irradiated and heat treated literally millions of carats of blue topaz this is what I came to believe.

Natural brown topaz will fade. More heat more fade all the way to colorless. Natural brown will never turn blue, it will only show blue if there was blue already in the stone.

Irradiated Topaz come out of the Linac with both brown and blue. The blue doesn't turn into blue, it masks it. The brown burns off at a lower temperature leaving the blue. But with enough heat you can also burn off the blue. Some oif the blue can fade so you must anneal the blue to get rid of the unstable color so it won't fade on your customers.

In order to know the way to treat the stones you must know what the source of the irradiation was Linear Accelerator (Electron Beam), Gamma Tank, Neutron Tank, or some combination of the above.

I must admit I never tried heat treating with a torch. Always in a temperature controlled oven.



I wasn't thinking about it stright I guess,from a chemical point of view,
obviously.
well,in my eyes it turned blue, :lol:
the heat itself not create any new elements in the stone.
hope I am getting it correct now..
so basically the blue is just the trace element (titanium? ) that was already in the stone to begin with ,and was masked by another elements that melted at a lower temperature?
that would also explain why I tried it also with a faded yellow Topaz from different origin that "turned" more greenish.
Thanks for the explanation.


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 10:14 pm 
Offline
Valued Contributor

Joined: Tue Jan 02, 2018 11:12 pm
Posts: 206
so it leads me to another question.. not sure I understand it.
what's exactly the Radiation exposure do to the crystal to enhanced it's color? ,
does it acts like a booster in a way? so the chemical composition changed after the exposure and than it have more % of this blue and brown trace elements inside it?


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 10:22 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
No, Let me try and explain is simple terms.

irradiation also doesn't create any new trace element either. The irradiation adds energy which moves electrons into a different valence states (change in orbit position). This creates color centers of brown and blue.

The brown color center is not as stable as the blue. So, when you heat the stone the brown color center electrons become unstable and fall back to their original position, destroying the brown color center.

The blue color center is more stable so remains until a higher heat is applied. The goal of the the heat treatment is to find the time/temperature formula that falls in the middle. You start low, take the stones out that changed to your satisfaction, heat again taking the good color stones out each time, and repeat.

This is the same idea used when heating dark Amethyst to a lighter color. Amethyst is FE rich quartz that has been exposed to natural radiation creating color centers.

I hope that I said things simple and clear enough for everyone to get the general idea.


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 10:47 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
In many cases you could get the same result by leaving treated stones in the sun, but that's a much slower/more annoying process. And not all browns sun-fade as quickly or completely as others (or at all).
If you don't mind the diversion, did you ever see any come out with pure yellows, Steve? I have heard of it, but 'yellow' is used a bit imprecisely in topaz (light brown/golden colors vs the pure yellows you sometimes see in ie Nigerian topaz).

I once got a (presumably treated no matter what they said) topaz with an odd smoky brown color. The blue and brown had blended unusually, giving it a strong grey cast. One day of sunlight and it was just light blue. Too bad those intermediate tones (and I guess greens sometimes) generally don't seem to hold up to regular sun exposure.

_________________
Rough and cut classic and exotic synthetic gems:https://store.turtleshoard.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 11:13 pm 
Offline
Valued Contributor

Joined: Tue Jan 02, 2018 11:12 pm
Posts: 206
1bwana1 wrote:
No, Let me try and explain is simple terms.

irradiation also doesn't create any new trace element either. The irradiation adds energy which moves electrons into a different valence states (change in orbit position). This creates color centers of brown and blue.

The brown color center is not as stable as the blue. So, when you heat the stone the brown color center electrons become unstable and fall back to their original position, destroying the brown color center.

The blue color center is more stable so remains until a higher heat is applied. The goal of the the heat treatment is to find the time/temperature formula that falls in the middle. You start low, take the stones out that changed to your satisfaction, heat again taking the good color stones out each time, and repeat.

This is the same idea used when heating dark Amethyst to a lighter color. Amethyst is FE rich quartz that has been exposed to natural radiation creating color centers.

I hope that I said things simple and clear enough for everyone to get the general idea.


Interesting. you definitely encouraged me do more reading about it...
Thanks Steve.


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 11:44 pm 
Offline
Gold Member

Joined: Mon May 26, 2014 9:42 pm
Posts: 1033
A very long time ago (40 years now), I took some colorless Mexican topaz to a local reactor at the university and asked them to radiate it for me. They did, then checked it before they gave it back to make sure it wasn't radioactive (it wasn't). It turned a very attractive coffee brown. Which would fade in sunlight pretty quickly - but my son still has some in a box that is still the same coffee brown 40 years later.


Top
 Profile  
Reply with quote  
 Post subject: Re: Topaz Irradiation treatment Identification
PostPosted: Thu Jun 18, 2020 11:55 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
Yes, back in the 80s we threw almost every mineral there was in different radiation sources. Many created some incredible colors. Most were not stable, and depending on the trace elements (mostly metallic ones) and the radiation source, they had residual radiation so were not saleable.

There was a lot of mexican topaz that was treated at that time. Some faded fast, and others slow so could be sold. But eventually they all pretty much faded back to their starting color. I am guessing there were some unhappy buyers out there. No laws about disclosure back then.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 10 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