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 9:04 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 13 posts ] 
Author Message
 Post subject: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 4:30 am 
Offline
Established Member

Joined: Tue Aug 16, 2022 6:13 pm
Posts: 17
You'd expect to be able to find a "true red" synthetic ruby pretty easily; but after having bought several, most of them are quite pink, magenta, or purplish, especially in brighter light:

Attachment:
P1010006.JPG
P1010006.JPG [ 6.31 MiB | Viewed 3952 times ]

Apologies for the photography skills. Good thing I'm not a photographer, or I wouldn't even be able to afford synthetics. :mrgreen:

Rows 1 and 2: synthetic rubies, including a "garnet" synthetic corundum that's supposed to be a deeper red (2nd row, 2nd stone).

Row 3: synthetics with added flux inclusions. They are actually a good color, but the clarity is obviously not good. I do wonder if the added inclusions alter the color...?

Row 4: natural rubies.

Row 5: glass filled.

I suppose my question is: why are so many ruby synthetics pink or magenta instead of vivid red? Skimping on chromium? No inclusions to deepen the color? Flame fusion can't make the same color intensity?

And as a follow-up, is there a reliable source for faceted vivid red synthetic ruby? I know RusGems has a couple hydrothermal, but they're very limited in selection.


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 11:16 am 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
I wonder if one factor is the orientation. A natural ruby will almost always be cut c-axis up, while a synthetic might be cut any which way.
It could also be the level of chromium or possibly codopants. The czochralski pulled laser ruby I've gotten my hands on has a nice rich red color and I believe that's only chromium. My friend Eric has cut a few https://www.instagram.com/reel/ChI2Guxv ... MyMTA2M2Y=

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


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 2:42 pm 
Offline
Gold Member
User avatar

Joined: Tue Apr 05, 2016 7:58 pm
Posts: 1424
Location: San Marcos, CA
Agree with Stephen with orientation can give slight color variations from cut stones from the same boule. Same I think would be true from boule to boule and the process of creation. Like natural corundums no two are exactly or perfectly created as equals.
In color comparisons using pretty much a different cut or shape to compare colors can give variations. One cut deeper in the pavilion and or the crown will deepen the color saturation appearance.
Someone correct me if wrong but Hydrothermal would not be corundums.
Older manufactured verses a newer synthetic might be cause.
Many synthetic corundum boules are split to relieve stress which can force a specific orientation onto the A/B axis depending on a specific size requirement. Whether you put the crown to the outter rhind of the boule or not.
The list goes on of possible causes. I also believe over the many years of synthetics there were several red colors two choose from as there was for the blue shades of sapphire.
I think in most your cause is due to a round next to cushion, cushion next a asscher style, oval next to round. Light play in each of these is different creating light return to the eye that is different.
What size stones are you in search of?

_________________
The Gem Garden
San Marcos, CA


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 5:30 pm 
Offline
Gold Member
User avatar

Joined: Tue Apr 05, 2016 7:58 pm
Posts: 1424
Location: San Marcos, CA
Here is a couple of photos of synthetic ruby that may help to understand the variances in shades of red.
I think the poster might benefit from the app "GemEWizard" that 1bwana1 and Barbra discussed a few months back to see the shades Ruby can be evaluated when purchasing. Here is the link to the thread. https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=6&t=26376&hilit=gemewizard

Attachment:
Various-SynRuby.jpg
Various-SynRuby.jpg [ 216.52 KiB | Viewed 3932 times ]


Some Chatham with a range of Orangy-Red to some areas where it is more a Redish-Purple or Purplish-red.

Attachment:
Chatum_Ruby.jpg
Chatum_Ruby.jpg [ 186.53 KiB | Viewed 3932 times ]

_________________
The Gem Garden
San Marcos, CA


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 6:18 pm 
Offline
Established Member

Joined: Tue Aug 16, 2022 6:13 pm
Posts: 17
Stephen Challener wrote:
I wonder if one factor is the orientation. A natural ruby will almost always be cut c-axis up, while a synthetic might be cut any which way.
It could also be the level of chromium or possibly codopants. The czochralski pulled laser ruby I've gotten my hands on has a nice rich red color and I believe that's only chromium. My friend Eric has cut a few https://www.instagram.com/reel/ChI2Guxv ... MyMTA2M2Y=


Ah, that’s probably a very big part of it. I knew that boules were generally cut a different orientation, but hadn’t considered if it could change the color that dramatically.

Doing some research, Richard Hughes has written about this at Lotus Gemology:

https://www.lotusgemology.com/index.php/library/articles/296-pleochroism-in-faceted-gems-lotus-gemology

About halfway down the page, there’s a section on synthetic pleochroism when it’s cut how most boules are.

I also found something in Wikipedia (take that for what it’s worth) that said many synthetic rubies use less chromium than natural ruby, causing a pink color:

“because of the low chromium level in these crystals they display a lighter red color than gemstone ruby and are referred to as pink ruby“

Under the Physical Properties tab of the Rubies wiki.

But anyway, that ruby does look really good. I wonder if a lot of it is just that they cut for weight and not color. Kinda surprising there aren’t synthetic manufacturers that set themselves apart by cutting perpendicular to the c-axis to have a better looking result, even if it would mean lower yields. I suppose I might have to find someone to cut one for me.

Looking for a 7mm round.


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 6:24 pm 
Offline
Established Member

Joined: Tue Aug 16, 2022 6:13 pm
Posts: 17
glhays wrote:
Here is a couple of photos of synthetic ruby that may help to understand the variances in shades of red.
I think the poster might benefit from the app "GemEWizard" that 1bwana1 and Barbra discussed a few months back to see the shades Ruby can be evaluated when purchasing. Here is the link to the thread. https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=6&t=26376&hilit=gemewizard

Attachment:
Various-SynRuby.jpg


Some Chatham with a range of Orangy-Red to some areas where it is more a Redish-Purple or Purplish-red.

Attachment:
Chatum_Ruby.jpg


I’ve been meaning to look at that app. The gem industry definitely needs better standardization of color. They’re so difficult to photograph, then you have differences in monitors, color spaces, camera settings… not to mention those who purposefully edit gem photos when selling.

It would be amazing if someone started an auction site that had consistent standards for photography of the products.


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Wed Aug 17, 2022 10:19 pm 
Offline
Gold Member

Joined: Thu May 12, 2016 2:18 am
Posts: 1542
glhays wrote:
Someone correct me if wrong but Hydrothermal would not be corundums.



Synthetic Hydrothermal Corundum is the growth method that most closely mimics the natural stone. Some of the best synthetics are grown using the hydrothermal method.


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Sat Aug 20, 2022 12:33 am 
Offline
Moderator
User avatar

Joined: Fri Jun 25, 2010 10:06 pm
Posts: 2267
Location: Chapel Hill, NC / Toronto, ON
Hey! To very, very directly answer your question: There are three major reasons for what you're seeing in synthetic ruby.

The first is that the colour caused by Cr3+ in corundum has a dose-dependent relationship. If you look at Verneuil Series 0 (Verneuil #1-10), these are all increasing concentrations of Cr3+, and you'll notice that it starts out as a very pale bright pink and gradually increases to a dark, pure red with no modifiers.

In melt-based growth (Verneuil, Czochralski, Kyropoulos, etc), Cr2O3 has a lower vapour pressure than Al2O3. This means that as you're growing the Al2O3 crystal, some of the chromium basically "boils away". And it's constantly boiling away during growth. That means that there's a theoretical maximum concentration these growth methods can produce. In flux-growth, the theoretical maximum concentration is higher, but if you try to add too much it'll interfere with the flux itself. In hydrothermal growth, the theoretical maximum is identical to natural growth processes.

So, no flame fusion or pulled synthetic ruby will ever get to the pure 100% red colour of a hydrothermal ruby. But you can still get pretty damn close - Verneuil #7, #8sp, #9, and #10 are all basically pure red. I've personally cut an 8mm round in Verneuil #7 and it was pure garnet red with no pink overtone.

The second is pleochroism. Let's look at Cr3+ from Emily Dubinsky's landmark paper from 2020, "A Quantitative Description of the Causes of Color in Corundum". For mid-range Cr3+ concentration, the ordinary ray is purplish and the extraordinary ray is pinkish, which mix together to produce a pinkish-purple. At very high Cr3+ concentrations, the ordinary ray is dark red and the extraordinary ray is medium red, which mix together to produce...red. But at very low Cr3+ concentration? The ordinary ray is lavender and the extraordinary ray is PEACH. So you're gonna see really strong pleochroic effects.

The third is dopant-related. To get a truly red ruby, you need a high concentration of Cr3+, but you also need iron as a dopant. Normally, Cr3+ produces a strong pinkish fluorescence in corundum, which can cause synthetic rubies to glow pinkish in daylight. Iron quenches that fluorescence, in much lower concentrations than the amount you'd need to turn the stone yellow. So, adding a tiny bit of iron will make the stone more red, without shifting the colour too much towards orange.


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Sat Aug 20, 2022 3:14 am 
Offline
Gold Member
User avatar

Joined: Tue Apr 05, 2016 7:58 pm
Posts: 1424
Location: San Marcos, CA
flat wrote:

Looking for a 7mm round.

Would be more than happy to cut it for you, just give me some criteria to go on.
Style of cut, standard, mixed, portuguese, etc.
Material preference of choice.

_________________
The Gem Garden
San Marcos, CA


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Sun Aug 21, 2022 2:03 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
Faceting 101 by Arya wrote:
In melt-based growth (Verneuil, Czochralski, Kyropoulos, etc), Cr2O3 has a lower vapour pressure than Al2O3. This means that as you're growing the Al2O3 crystal, some of the chromium basically "boils away". And it's constantly boiling away during growth.

This is not insurmountable. GAGG contains gallium which has a much, much lower vapor pressure, so they just add gaseous gallium to the growth atmosphere at an even higher level so it actually gains some. Presumably this could be done with ruby as well if needed.

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


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Mon Aug 22, 2022 12:52 am 
Offline
Established Member

Joined: Tue Aug 16, 2022 6:13 pm
Posts: 17
Faceting 101 by Arya wrote:
Hey! To very, very directly answer your question: There are three major reasons for what you're seeing in synthetic ruby.
(snip)


Whoa, thanks for taking the time to write that! It explains a lot.

I know it would quench fluorescence, but I did find an alert from GIT about a synthetic ruby that contained almost natural levels of iron (and gallium). I wonder if they did that to alter the red color, or if they were just impurities somewhere along the line.


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Mon Aug 22, 2022 12:55 am 
Offline
Established Member

Joined: Tue Aug 16, 2022 6:13 pm
Posts: 17
glhays wrote:
Would be more than happy to cut it for you, just give me some criteria to go on.
Style of cut, standard, mixed, portuguese, etc.
Material preference of choice.


Probably just a 7mm round brilliant with #8. I was wearing a natural ruby in that size and shape, but I work with my hands, and was afraid of breaking or losing it. Hence the search for a synthetic that at least has the right color. :mrgreen:


Top
 Profile  
Reply with quote  
 Post subject: Re: Why are so many synthetic rubies off-color?
PostPosted: Sun Sep 04, 2022 4:42 pm 
Offline
Moderator
User avatar

Joined: Fri Jun 25, 2010 10:06 pm
Posts: 2267
Location: Chapel Hill, NC / Toronto, ON
Stephen Challener wrote:
Faceting 101 by Arya wrote:
In melt-based growth (Verneuil, Czochralski, Kyropoulos, etc), Cr2O3 has a lower vapour pressure than Al2O3. This means that as you're growing the Al2O3 crystal, some of the chromium basically "boils away". And it's constantly boiling away during growth.

This is not insurmountable. GAGG contains gallium which has a much, much lower vapor pressure, so they just add gaseous gallium to the growth atmosphere at an even higher level so it actually gains some. Presumably this could be done with ruby as well if needed.

Yeah, growers will do this for things like Czochralski growth when they're trying to hit a very specific concentration of a dopant with a lower vapour pressure. But for flame fusion? Naaaaahhhhhh lol


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 13 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 13 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