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 5:56 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 4 posts ] 
Author Message
 Post subject: GIA Finds Synthetic Ruby Layer on Natural Gemstones
PostPosted: Mon Apr 02, 2018 11:51 am 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 21602
Location: San Francisco
GIA Finds Synthetic Ruby Layer on Natural Gemstones

Brecken Branstrator for National Jeweler wrote:
April 2, 2018

Carlsbad, Calif.--The Gemological Institute of America’s New York lab recently had a gemstone submitted for identification it hasn’t seen before.

According to an article by Tyler Smith and Hollie McBride in the winter 2017 issue of “Gems & Gemology,” the lab received two loose oval mixed-cut red gems for identification. Upon testing, the stones revealed refractive indices slightly higher than normal for corundum.

Higher refractive indices have been reported before for chromium-diffused corundum, in which extra chromium is added during heating to enhance the color. So, the article states, to the naked eye, the stones simply appeared to be chromium diffused and displayed red color concentrations at the intersections of the facets.

But further microscopic examination revealed a thin layer, about 0.3 mm thick, of “synthetic overgrowth”—a layer of lab-grown ruby that gave the stone its color—with a natural, almost-colorless sapphire at the core.

The authors said the two stones looked similar to Lechleitner synthetic overgrowth emeralds, named for Johann Lechleitner, who pioneered the process of giving a near-colorless beryl seed its green color with a synthetic emerald overgrowth in 1960. (The GIA’s lab in Carlsbad, coincidentally, received a Lechleitner emerald for identification around the same time the rubies were submitted.)

Lechleitner also experimented with ruby overgrowth on both synthetic and natural corundum seeds.

While his specimens contained a number of elements, the two rubies submitted to the GIA were missing one—molybdenum—indicating there were different growth conditions present, according to the G&G article.

It noted that while this isn’t the first report of synthetic ruby overgrowth on natural sapphire seeds, it is the first time material featuring such aspects has been submitted to its New York and Carlsbad laboratories for identification.

“The resurfacing of these vintage overgrowth synthetics shows that once a material is in the trade, it is here to stay,” Smith and McBride said.


Top
 Profile  
Reply with quote  
 Post subject: Re: GIA Finds Synthetic Ruby Layer on Natural Gemstones
PostPosted: Thu Nov 29, 2018 6:05 pm 
Offline
Valued Contributor

Joined: Thu Aug 20, 2009 10:36 am
Posts: 118
Location: New York
Hi all,

I haven't been able to keep up with many of these threads over the past few months, as a result I just noticed this entry. For those interested, here is the original article on this material, which I published in 2002.

Best regards and Happy Holidays to all,
Christopher P. Smith


Attachments:
“Diffusion-Ruby”-Proves-to-be-Synthetic-Ruby-Overgrowth-on-Natural-Corundum.pdf [479.04 KiB]
Downloaded 599 times
Top
 Profile  
Reply with quote  
 Post subject: Re: GIA Finds Synthetic Ruby Layer on Natural Gemstones
PostPosted: Thu Nov 29, 2018 6:28 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
I wonder at what point this overgrowth should stop being called synthetic ruby or corundum--with chromium at structural concentrations and an RI way outside of corundum's range I would think it could be appropriate to consider it a different material (or a different mineral if it were naturally occurring.)

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


Top
 Profile  
Reply with quote  
 Post subject: Re: GIA Finds Synthetic Ruby Layer on Natural Gemstones
PostPosted: Fri Nov 30, 2018 10:25 am 
Offline
Valued Contributor

Joined: Thu Aug 20, 2009 10:36 am
Posts: 118
Location: New York
Hi Stephen,

When I was first examining this material, I had a similar thought and so wanted to see if for example the Raman signature of the overgrowth had shifted from standard corundum. It hadn't. Also, we do sometimes record elevated levels of both chromium and iron in natural corundum, which can be individually above 1 wt%.

Solid solution series between Al2O3 and Cr, Fe, Mg and other elements have been proven and demonstrated experimentally. However, I am not certain at what stage/concentration/formulation it might no longer be appropriate to classify such a 'synthetic' as no longer corundum. However for the material we've analyzed thus far, it would still be appropriately classified as a synthetic corundum/ruby.

Best regards,
Christopher P. Smith


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 4 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 7 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