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GIA vs. IGI Grading of Lab Diamonds

Ada Diamonds CEO

Rough_Rock
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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:




Screen Shot 01-09-20 at 11.48 AM.JPG

Screen Shot 01-09-20 at 11.47 AM.JPG
 

Blahthing

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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

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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.
 

SJEsper

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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

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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

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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'!
 

OoohShiny

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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

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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

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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.


"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:
 

Blahthing

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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

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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

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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

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@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

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Shayne808

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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

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.... 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!
 

Lessics

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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).
 
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