GIA vs. IGI Grading of Lab Diamonds

[Ada Diamonds CEO]

PSers-

New guy here, but I want to challenge a 'trueism' that I've seen in a few threads stating that IGI is soft/easy in their grading and that you need to add 1-2 letters to an IGI grade to get the 'true' GIA or AGS grade. Having worked with thousands of lab diamonds over the last 5 years, I find this to simply not be the case (excluding IGI Mumbai - we refuse to work with Mumbai graded lab diamonds).

We've sent multiple lab diamonds to GIA for secondary grading and never seen this 1-2 letter haircut in the diamonds. Virtually all the time the gradings are in lockstep. In fact, I've seen IGI grade a diamond a 'G' color, and then GIA secondary grade the exact same diamond as a D, E, or F (and then print 'Colorless' on the grading report). See GIA and IGI certs for the same diamond attached.

Now that being said, there variations in colors in lab diamonds that do not occur in natural diamonds, and not all letter grades are equal. IE there are some F colors that are far beneath our quality standards, and occasionally we'll see a lovely H color. That being said, I strongly encourage you to stay at G or above!

Lastly, here's analysis of GIA & IGI dual-graded mined diamonds and found that IGI was actually stricter than GIA on color grading:

https://www.diamondscreener.com/edu...ification-labs-gia-vs-igi-grading-and-prices/

 

[denverappraiser]

I agree. There is no simple conversion.

 

[Blahthing]

That’s good to know. I’m looking to buy a lab diamond and the only Certs I can find are IGI and I was a bit worried. Thanks for sharing.

 

[denverappraiser]

GCAL is also big in grading synthetics if you prefer a different lab. Both are fine companies. GIA is not popular with sellers for the reasons discussed above.

 

[Meowingtons]

Hi @Ada Diamonds CEO , thanks for the post - it's certainly useful to know and piqued my interest to learn more. I refer to the below:

Now that being said, there variations in colors in lab diamonds that do not occur in natural diamonds, and not all letter grades are equal. IE there are some F colors that are far beneath our quality standards, and occasionally we'll see a lovely H color. That being said, I strongly encourage you to stay at G or above!

Can you provide clarification on what do you mean by there are variations in colors in lab diamonds that do not occur in mined diamonds? And how does this affect the letter grades and its variance?

Also, how about clarity grading? I have read that some lab diamonds have striation issues that mined diamonds don't - does this affect the clarity grade and is this taken into account when grading companies are grading the stones?

 

[OoohShiny]

GCAL is also big in grading synthetics if you prefer a different lab. Both are fine companies. GIA is not popular with sellers for the reasons discussed above.

I believe that GCAL also include info on whether an MMD is Type IIa, which I'm not sure I've seen on IGI?

 

[OoohShiny]

Can you provide clarification on what do you mean by there are variations in colors in lab diamonds that do not occur in mined diamonds? And how does this affect the letter grades and its variance?

Also, how about clarity grading? I have read that some lab diamonds have striation issues that mined diamonds don't - does this affect the clarity grade and is this taken into account when grading companies are grading the stones?

I am wondering if we are talking about the undertones in diamonds - these are not reported on GIA grading reports on Mined diamonds either!

John Pollard has previously posted about Stria, and there are some useful pictures on MMD inclusions on the HPD website

I'm not sure Stria is (are?) taken into account in grading, but then as Garry H has posted recently, GIA does not grade 'haze' in Mined stones, and has posted an example of an IF stone that was downgraded by the vendor for being 'sleepy'!

 

[denverappraiser]

I believe that GCAL also include info on whether an MMD is Type IIa, which I'm not sure I've seen on IGI?

Synthetic diamonds are all type IIa, at least for now.

 

[OoohShiny]

Synthetic diamonds are all type IIa, at least for now.

Thank you for the clarification!

I thought that was the case - Ada has stated on another thread that HPHT stones from (one of) the largest manufacturers are IIb, so I'm feeling a bit confused, lol.


Also, to come back to my comment on IGI not mentioning Type, it seems they do - as on this grading report: https://e-igi.com/viewpdf.htm?itemno=LG11211515 - but I'm not sure if it's a special request to include it??

 

[denverappraiser]

Ada is a credible source. The difference between IIa and IIb has to do with boron content. IIa is none, IIb is 'significant'. This can be important for people who are using the stones for non-gemological purposes like computers and other electronics, but it requires the grower to add an unusual dopant to get there.

 

[Ada Diamonds CEO]

Can you provide clarification on what do you mean by there are variations in colors in lab diamonds that do not occur in mined diamonds? And how does this affect the letter grades and its variance?

There are a number of unnatural defects that occur in HPHT and CVD growth that (pragmatically) do not occur in (99.99%+) of mined diamonds. For example, HPHT grown diamonds can have metallic inclusions, as the diamonds are grown in a metal flux, and CVD diamonds can have voids in the crystal structure as the diamonds are grown in a vacuum.

Just as there are quality differences in mined diamonds of equivalent grading, the same is true in lab diamonds. As much as I'd like to list out each and every defect we check for in our QC process for the good of the PS community, I have to consider that information proprietary, as our curation and quality control is the reason that our clients choose us over budget eCommerce sites.

Also, how about clarity grading? I have read that some lab diamonds have striation issues that mined diamonds don't - does this affect the clarity grade and is this taken into account when grading companies are grading the stones?

Sadly, a diamond with striations will not be reflected on the clarity grade of a diamond, as they're not a macro defect in the diamond such as a feather, needle, cloud, twinning, foreign material, etc.

So the diamond is negatively impacted in light performance, but that impact is not currently disclosed during grading.

Observations on CVD-Grown Synthetic Diamonds: A Review | Gems & Gemology

Explores statistical data and defining characteristics of gem-quality CVD synthetic diamonds examined by GIA since 2003.

www.gia.edu

"n figure 13, images A and C illustrate a trend seen by GIA researchers in the last few years: a series of parallel bands, likely indicating interruptions during the CVD growth sequence. If a CVD specimen is grown for too long, single-crystal growth becomes polycrystalline growth (Nad et al., 2015). The only remedy is to stop the growth process, remove the crystal from the reactor, and polish away the non-gem polycrystalline diamond. The sample can then be returned to the reactor for the growth process to resume. The chemical composition within the gas phase and on the diamond surface is slightly different at start-up than when the reactor has reached a steady-state condition. "

Ada is a credible source. The difference between IIa and IIb has to do with boron content. IIa is none, IIb is 'significant'. This can be important for people who are using the stones for non-gemological purposes like computers and other electronics, but it requires the grower to add an unusual dopant to get there.

Thank you for the kind words! I wish that all (non-fancy color) lab diamonds were type IIa; however, the sad truth is that many HPHT grown lab diamonds are in fact type IIb, which results in a variety of properties that reduce the desirability of the diamond.

The even sadder truth is that these diamonds are being sold without disclosure to unsuspecting customers around the world.

Even sadder than that - gemological labs have started to see undisclosed treatment of these diamonds to mask/hide some of the evidence of these defects.

See chart #1 - most of the diamonds from a leading HPHT producer were determined to be type IIb by GIA:

Large Colorless HPHT-Grown Synthetic Gem Diamonds from New Diamond Technology, Russia | Gems & Gemology

Examines a new source of colorless and near-colorless gem-quality HPHT synthetic diamonds using spectroscopic and gemological analysis.

www.gia.edu

 

[Dm4er]

That being said, I strongly encourage you to stay at G or above!

Hi Ada, appreciate the detailed insight!

As a starting point, do you also have a suggested clarity level that we should look to stay above?

 

[Blahthing]

How can we tell if the diamond is HPHT or CVD? I can’t see it on the certificate report. Or is it just a gamble? And are these striations visible under magnification?

 

[OoohShiny]

How can we tell if the diamond is HPHT or CVD? I can’t see it on the certificate report. Or is it just a gamble? And are these striations visible under magnification?

Some grading reports include a sentence stating what the stone is, but not all.

Some producers claim to only produce one variety, but then you have to know who produced the stone and if they are telling the truth - for example, Takara have been claiming to use only HPHT processes but it seems they may be using CVD... (Yet to be confirmed for definite either way, I think.)

Striations are the subject of a lot of discussion on here - some experts have said that they reduce 'life' in the diamond but others have said that they are invisible when on the finger/neck/ear. Without seeing an example for myself, I think HPHT represents a 'safer' or 'mind-clean' option (because it seems to have less/zero striations) but there have also been some lovely CVD stones, so nothing is simple... lol

 

[Blahthing]

So many factors to consider that I didn’t know before. It seems like such a gamble but my partner and I still prefer it over a mined diamond. I hope the one we bought looks good!

 

[Kayelle]

@OoohShiny - I’m a bit confused. I thought all lab grown were CVD and that HPHT was a process applied to mined diamonds to improve colour, or whatever? Can lab grown diamonds be created with HPHT?

 

[Ada Diamonds CEO]

@OoohShiny - I’m a bit confused. I thought all lab grown were CVD and that HPHT was a process applied to mined diamonds to improve colour, or whatever? Can lab grown diamonds be created with HPHT?

Yes, diamonds can be grown via HPHT.

Here's a quick intro into the two different growth techniques:

https://www.adadiamonds.com/introduction-to-lab-diamonds

 

[Kayelle]

Yes, diamonds can be grown via HPHT.

Here's a quick intro into the two different growth techniques:

https://www.adadiamonds.com/introduction-to-lab-diamonds

Thank you

 

[Shayne808]

I have been looking at Brilliant earth and JamesAllen for lab grown Diamonds. I notice that when you search James Allen the highest the Cut can go up to is Ideal. But when searching Brilliant Earth it goes from very good-ideal-super ideal. But both are IGI Certified. I am wondering if Brilliant Earth just sells betters quality diamonds.

2) I see from Above that for lab grown diamonds it is best to stay at G or above in color. What could you folks recomend in Clarity and Cut? I am not sure how big the difference is between very good, ideal and super Ideal??? Also for clarity, should I stay at VVS2 and above or VS1 and above? The prices go up significantly.

Thank you for your time.

 

[sunandsky]

.... not all letter grades are equal. IE there are some F colors that are far beneath our quality standards, and occasionally we'll see a lovely H color. That being said, I strongly encourage you to stay at G or above!

Hi @Ada Diamonds CEO, thanks for these interesting articles and commentary. Can you say more about the quote above? Why are the f’s below your quality standards? Which h’s are better than others? Why should we stay at g and above? Thanks very much!

 

[xxxxxx]

Hi @Ada Diamonds CEO, thanks for these interesting articles and commentary. Can you say more about the quote above? Why are the f’s below your quality standards? Which h’s are better than others? Why should we stay at g and above? Thanks very much!

He stated above that he won’t go into more detail as that is what he does for a living (checking the quality of lab diamonds for his paying customers).


But for a short summary.

CVD grown Diamonds
+ often type lla (purest type of diamond)
- Often has striation issues
- colors below G can look gray, brown and dark. And are all in all just rather unappealing


HPHT Grown Diamonds
+ no striation issues
+ clarity is often really nice
- often have a undisclosed blue nuance (looks unnatural according to ada diamonds ceo)
- are most often type llb diamonds (not as pure as type lla)


There might be Fs with terrible clarity and Hs that actually look like a lively G or F. That can only be determined really when you have the diamond in your hand. Because I can’t even discern the blue nuance on the 360 diamond videos (even if the certificate states it).

 

[Ada Diamonds CEO]

Hi @Ada Diamonds CEO, thanks for these interesting articles and commentary. Can you say more about the quote above? Why are the f’s below your quality standards? Which h’s are better than others? Why should we stay at g and above? Thanks very much!

You're most welcome. If you can't tell, I love geeking out about lab diamonds

My point is this - mined diamonds all come out of a single, billion year old 'lab' and have largely the same atomic defects, and well known properties.

Man made diamonds come from dozens of labs, may have a one or more post growth treatments applied, and to further complicate things, one grower may have 2 or 3 generations of growth equipment running at the same time so you need to know not just the grower, but the machine!

I could put a dozen 1ct round G color VS1 clarity stones of near identical dimensions in front of 100 laypeople and the consensus on which stones were desirable and which were unexceptional would be quite consistent.

Unfortunately, do the same thing with *videos* of a dozen G VS1 stones, and there won't be consensus.

About 2/3s of what we sell today is DEF, and the other 1/3 is almost all G color. Occasionally we sell H colors when a client is budget constrained and wants to hit that 2 or 3 carat milestone. We are quite selective on the H colors we sell, and generally only sell untreated Hs.

I wish I could only sell DEF (I'm a color snob), but there aren't enough goods on the market!

He stated above that he won’t go into more detail as that is what he does for a living (checking the quality of lab diamonds for his paying customers).

There might be Fs with terrible clarity and Hs that actually look like a lively G or F. That can only be determined really when you have the diamond in your hand. Because I can’t even discern the blue nuance on the 360 diamond videos (even if the certificate states it).

Correct. At the end of the day, I run a business and I can't just open source our entire QC process
One thing to add to your list - CVD diamonds are often color treated to remove brown tinges. If the treatment is mild/minor, it can produce stunning EF color goods, other treatment is quite heavy and produces grey, cloudy, unexceptional goods, even in the FGH color range.

As to discerning quality from lightbox videos... Some wholesalers will muck with the color temp of their lightbox and adjust the white balance of their DSLR to 'beautify' their diamonds. I recently caught wind that other wholesalers are simply faking their videos, using a video of better color diamond with an inclusion map that approximately matches the cert.

Let me say this about videos - we consistently reject and immediately return 30-35% of the stones we request for inspection. 400 pixel videos and paper (certs) can be used to weed out the khazeray (junk) but can't be used to find stunning goods.

 

[xxxxxx]

This makes buying lab diamonds for European Customers so hard!

Here is a ghastly example of a CVD Diamond with striation. I feel bad for the person purchasing this stone

1.71ct J VS1 Private Reserve August Vintage Cut OEC Lab Grown Diamond

Cut to perfection. :) A beautiful new OEC by yours truly. Diamond Details Measurements 7.54 - 7.58 x 4.92mm Cut Id Polish VG Symmetry EX Fluorescence None Culet none Report IGI Table 46.5 Depth 60.6%

www.distinctivegem.com

 

[OoohShiny]

This makes buying lab diamonds for European Customers so hard!

Here is a ghastly example of a CVD Diamond with striation. I feel bad for the person purchasing this stone

1.71ct J VS1 Private Reserve August Vintage Cut OEC Lab Grown Diamond

Cut to perfection. :) A beautiful new OEC by yours truly. Diamond Details Measurements 7.54 - 7.58 x 4.92mm Cut Id Polish VG Symmetry EX Fluorescence None Culet none Report IGI Table 46.5 Depth 60.6%

www.distinctivegem.com

I believe @Rhino has previously stated that he inspects all his stones to make sure that light performance is not affected by any characteristics a given stone may have, and that striations are not apparent when on the finger, but I think it is fair to say that they are quite noticeable when zoomed in on a screen.

 

[Rhino]

This makes buying lab diamonds for European Customers so hard!

Here is a ghastly example of a CVD Diamond with striation. I feel bad for the person purchasing this stone

1.71ct J VS1 Private Reserve August Vintage Cut OEC Lab Grown Diamond

Cut to perfection. :) A beautiful new OEC by yours truly. Diamond Details Measurements 7.54 - 7.58 x 4.92mm Cut Id Polish VG Symmetry EX Fluorescence None Culet none Report IGI Table 46.5 Depth 60.6%

www.distinctivegem.com

LOL... I'm actually going to feel pretty awesome for the person who gets it. It's a perfectly beautiful diamond and cut magnificently with no impact on the transparency whatsoever. Fact of the matter is *most* CVD diamonds have it and the truth is that you can't see it in the majority of online photography. I don't know what your personal experience is screening and vetting diamonds with grain or strain under polarizing filters through a microscope but I've been doing it with earth grown for over 2 decades and weeding out diamonds for clients where it does in fact impact transparency but if you know something I don't I'm open to listening. Since we are also cutting lab grown and now I'm also offering a vetting service for JamesAllen my vetting hasn't changed and now extends into the world of lab grown.

I believe @Rhino has previously stated that he inspects all his stones to make sure that light performance is not affected by any characteristics a given stone may have, and that striations are not apparent when on the finger, but I think it is fair to say that they are quite noticeable when zoomed in on a screen.

Exactly.

Peace,
Rhino

 

[Rhino]

Here are two examples I recently shot under polarization in a round and oval i was vetting. If the transparency is impacted I make the client aware of it and I can also generally capture this in HD video in the lighting environment it is impacted in.

 

[Rhino]

and @Ada Diamonds CEO ... good stuff man