Cutwise & 'My' Round Brilliant - The rabbit hole just got deeper!

[MackPUK]

With the kind help of this forum (and individuals like @DejaWiz) I recently purchased a beautiful 2.5ct LG Round Brilliant

I did a ton of research and learnt the basics re: cut angles, proportions, the dynamic nature of various angles working together, material quality, symmetry, the different growing processes & 'quirks' they can introduce, the differences between the lab reports - how stringent (or not) they are - what they can tell you vs what they can't and so on.

This REALLY helped me narrow down options leading quickly to the stone I purchased (I admit partly as it came with an AGS0 Ideal Report along with the GIA which gave some piece of mind when buying remote)

Fast forward - I am 100% happy with the stone (it's still being set) but my interest did not stop post purchase and I recently heard about 'Cutwise.com' - which I find fascinating. I then read some of the longer threads here (between some of the most knowledgeable and expert members) on the wider subject which were very interesting - although for a layman like me slightly tricky to follow at times.

Anyway, that led me to idly search cutwise for stones with similar specs to mine to see what more information could be found - and then realised 'my' stone was in the database - hence the deepening rabbit hole.

I've now read a bunch of Octonus info but I am really interested to understand from some of the experts (@Serg I assume being the go-to here!?) how to interpret some of the less familiar information (e.g. what should I look for in a darkfield view, what can I glean from ETAs and DETAs, what is considered a 'good' deviance for key angles (e.g. Pa/Ca) etc)

For reference this is my stone: cutwise.com/diamond/1035060

With thanks in advance to anyone that can help me learn more

 

[0515vision]

Wow!! Cutwise looks amazing! What vendor did you use? I'm accustomed to seeing those gorgeous videos from Brian Gavin, but maybe lots of diamonds get those glamour shots?

Congrats on your gorgeous find!

 

[MackPUK]

Thx

I sourced through an online site (77Diamonds who have a UK presence). It wasn’t a stone they had local so I guess the original producer / cutter / seller used the same technology to get the pics which uploads to cutwise (https://www.octonus.com/dibox/dibox-2_0 I think!) Im sure other vendors use the same/similar photography technology to get their pics/videos also.

I think I was slightly lucky to find this stone in the ‘normal’ list on that site rather than their ‘Cupids Ideal’ list which is where other GIA+AGS options are usually listed at inflated prices (and it wasn’t on any of the other usual sites like LGD, Calavera etc either!)

 

[0-0-0]

How cool to find your diamond on cutwise! I think it’s a shame that most manufacturers and vendors don’t share all the cut information that they have access to.

I think darkfield is typically used to spot inclusions easier. If you look at the sarins of the branded H&A rounds shared by others, the pavilion angles typically have a range of around 0.3 degrees and the crown angles typically have a marginally higher range.

 

[Serg]

With the kind help of this forum (and individuals like @DejaWiz) I recently purchased a beautiful 2.5ct LG Round Brilliant

I did a ton of research and learnt the basics re: cut angles, proportions, the dynamic nature of various angles working together, material quality, symmetry, the different growing processes & 'quirks' they can introduce, the differences between the lab reports - how stringent (or not) they are - what they can tell you vs what they can't and so on.

This REALLY helped me narrow down options leading quickly to the stone I purchased (I admit partly as it came with an AGS0 Ideal Report along with the GIA which gave some piece of mind when buying remote)

Fast forward - I am 100% happy with the stone (it's still being set) but my interest did not stop post purchase and I recently heard about 'Cutwise.com' - which I find fascinating. I then read some of the longer threads here (between some of the most knowledgeable and expert members) on the wider subject which were very interesting - although for a layman like me slightly tricky to follow at times.

Anyway, that led me to idly search cutwise for stones with similar specs to mine to see what more information could be found - and then realised 'my' stone was in the database - hence the deepening rabbit hole.

I've now read a bunch of Octonus info but I am really interested to understand from some of the experts (@Serg I assume being the go-to here!?) how to interpret some of the less familiar information (e.g. what should I look for in a darkfield view, what can I glean from ETAs and DETAs, what is considered a 'good' deviance for key angles (e.g. Pa/Ca) etc)

For reference this is my stone: cutwise.com/diamond/1035060

With thanks in advance to anyone that can help me learn more

The simplest question is about Darkfield. This type of lighting is used in laboratories to detect internal defects in diamonds. With the magnification and resolution used in Dibox 2.0, you can typically observe inclusions at the VS2/SI1 boundary, and more rarely at VS1/VS2. In the Darkfield video, no internal inclusions are visible (only some surface dust can be seen), which is consistent with the VS1 clarity grade.


A more advanced question concerns the tolerances in pavilion and crown main angles. Considering that the Optical Symmetry grade is 9+, the cut is a classic RBC, and Optical Performance is EX, there is no real reason to analyze individual facet angles.
However, since you're interested: in the I3D report, you can see that the variation in pavilion main angles is just 0.1°, and for the crown it’s slightly larger (with a maximum deviation of 0.25°). But if we factor in a table tilt of 0.1° (which this diamond either actually has or it's due to a minor misalignment during scanning), then all the main angles fall within ~0.1° range — which is an excellent result.


Even a 0.2° spread in pavilion or crown main angles is considered very good. The azimuth deviation is around 0.4°, which is also a very good result (especially considering scanner accuracy limits).


Grown Diamond Corporation did a very high-quality job in 2024. In contrast, in 2025, RBC LGD cutting standards have dropped significantly, in an effort to cut costs due to the price drop in lab-grown diamonds. There is now intense competition over price, whereas in 2024 cutters were still trying to compete on quality.


As for ETAS and DETAS, there’s no real reason to analyze them for such a well-cut RBC diamond. These tools become important if you're planning to buy a fantasy cut, which functions very differently from a round brilliant. In such cases, it’s necessary to thoroughly study ETAS and DETAS imagery.

The only critique I could make of this cut is the -3% spread, which results from a slightly thick girdle (4%), done in order to reach the 2.5 ct weight threshold.


In reality, this diamond visually appears more like a 2.42–2.45 ct round brilliant, but it's unlikely that this difference would be noticeable to the naked eye — it’s quite minimal. However, since the difference does exist and the diamond sits right around a weight transition point, this is a reasonable and objective basis to request a discount.


After all, what truly matters to you is that the diamond looks bigger, not that it simply weighs more, right?

 

[MackPUK]

The simplest question is about Darkfield. This type of lighting is used in laboratories to detect internal defects in diamonds. With the magnification and resolution used in Dibox 2.0, you can typically observe inclusions at the VS2/SI1 boundary, and more rarely at VS1/VS2. In the Darkfield video, no internal inclusions are visible (only some surface dust can be seen), which is consistent with the VS1 clarity grade.


A more advanced question concerns the tolerances in pavilion and crown main angles. Considering that the Optical Symmetry grade is 9+, the cut is a classic RBC, and Optical Performance is EX, there is no real reason to analyze individual facet angles.
However, since you're interested: in the I3D report, you can see that the variation in pavilion main angles is just 0.1°, and for the crown it’s slightly larger (with a maximum deviation of 0.25°). But if we factor in a table tilt of 0.1° (which this diamond either actually has or it's due to a minor misalignment during scanning), then all the main angles fall within ~0.1° range — which is an excellent result.


Even a 0.2° spread in pavilion or crown main angles is considered very good. The azimuth deviation is around 0.4°, which is also a very good result (especially considering scanner accuracy limits).


Grown Diamond Corporation did a very high-quality job in 2024. In contrast, in 2025, RBC LGD cutting standards have dropped significantly, in an effort to cut costs due to the price drop in lab-grown diamonds. There is now intense competition over price, whereas in 2024 cutters were still trying to compete on quality.


As for ETAS and DETAS, there’s no real reason to analyze them for such a well-cut RBC diamond. These tools become important if you're planning to buy a fantasy cut, which functions very differently from a round brilliant. In such cases, it’s necessary to thoroughly study ETAS and DETAS imagery.

The only critique I could make of this cut is the -3% spread, which results from a slightly thick girdle (4%), done in order to reach the 2.5 ct weight threshold.


In reality, this diamond visually appears more like a 2.42–2.45 ct round brilliant, but it's unlikely that this difference would be noticeable to the naked eye — it’s quite minimal. However, since the difference does exist and the diamond sits right around a weight transition point, this is a reasonable and objective basis to request a discount.


After all, what truly matters to you is that the diamond looks bigger, not that it simply weighs more, right?

Wow!

Thank you for the comprehensive response.

I guess it's always comforting to know that I have a 'good one' and that the minor details are not necessarily important in this specific case but as someone who has become very interested in this world it's great to understand (even a little bit!) more about what can be gathered from the different tools/images/stats etc.

Also, thanks for the pointers on what to look for in these images - I am pretty sure this won't be my final purchase so this will be useful in time.

Regards the -3% and it resulting in closer to 2.42-2.45ct true face up size - that is a non-issue for me. 2.5ct was pretty near the top of my size range (this will be set in a 6 prong hand forged platinum solitaire with a rex collet on a 5.75 finger so will have a fairly large coverage %)

Having seen many, many more pictures and comparisons since purchase the very minor difference (on the smaller side) is probably a plus in my situation.

That said, I totally understand why stones might be cut with these quirks (thicker girdles, deeper angles etc) in order to hit 'magic' weights for resale purposes and that this can lead to some overpricing.

Of course, I didn't have this detailed info to hand at the time of purchase but I don't believe I paid over the odds (comparing retail) at the time.

Searching for another GIA stone with similar specs (from 2.4ct) on sites like loosegrowndiamond, Adiamor (or using Pricescope etc) indicates it would be still be hard to get another for the same price

Most of the options I can find with comparable proportions (and GIA report) seem start in the $2k range (for CVD) and go up. I did find one similar HPHT option with VVS clarity on Calavera for approx $1500 but it faces up a fraction smaller)

None of these lower priced options have the AGS0 report addendum (I know that doesn't mean they wouldn't qualify if tested) and most look noticeably worse in the 360's I've viewed so I'm very comfortable/happy with what I have in hand (for transparency I paid the equivalent of $1400USD)

 

[Lexus]

@Serg
Re. Even a 0.2° spread in pavilion or crown main angles is considered very good. The azimuth deviation is around 0.4°, which is also a very good result (especially considering scanner accuracy limits).

The term "VERY GOOD" in diamond grading is typically misinterpreted. A VERY GOOD grade is considered not good enough.

Here, as Sergey describes, the variation in slope angle and azimuth angle is outstanding (unimaginable in normal terms). Labs permit a variation of up to 1° to qualify for Excellent symmetry.

 

[MackPUK]

Thanks Lexus

Yes, with usual lab grading nomenclature I am aware that 'very good' is far from good enough (and, for that matter, GIA 'Excellent', IGI 'Ideal' and GCAL8x still have varying ranges within their grades that allow for less than ideal performance) - that is one reason I was keen to find a stone with ASET images alongside the reports/videos as I was buying remote (or in my case the AGS supplement which gave similar confidence).

However, as it pertains to this discussion, I read/interpreted the comment as (I think!) it was intended by @Serg i.e. the cut on this stone is genuinely very good in the real sense of the words

I know my partner won't care about all this fine detail (though it will come as no surprise to her that I have gone this deep) but I love it

 

[0515vision]

Did you enjoy your experience with 77 diamonds?

We’ve recommended it from time to time to European buyers, but of course we don’t know its reputation as well as say Ritani, WF, BG, Loosegrown Diamond, Diamond By Lauren, etc.

 

[MackPUK]

Did you enjoy your experience with 77 diamonds?

We’ve recommended it from time to time to European buyers, but of course we don’t know its reputation as well as say Ritani, WF, BG, Loosegrown Diamond, Diamond By Lauren, etc.

Yes, for me it was a very simple transaction with clear communications and the stone arrived ahead of schedule (it was not one they had in stock in the UK) so I didn't visit them in person - it was all conducted online/over email.

Their search function is one of the better ones I've used, allowing for simple search through quick drop downs etc and it includes some useful 'advanced' search items - and it doesn't lose your search settings when clicking into each stone details and back (unlike Calavera which is an awful search in comparison!)

Also has the ability to search by report number which is useful for comparing prices across different sites.

Ordering was simple, email communication throughout was responsive etc. The diamond came in a (pretty large) very nicely presented box with the invoice information in a colour matched little folio inside, plus separately wrapped polishing cloth and branded 'leather' pouch with the loose diamond wrapped inside. Overall a really nice quality presentation even for a loose stone.

I'd have no issue purchasing through them again or recommending them as long as the price is right.

 

[Garry H (Cut Nut)]

I dislike darkfield clarity grading.
Consumers see diamond in a front lit environment and they title diamonds as well as having two eyes viewing from slightly different angles when examining a diamond.
The GIA has largely moved to AI back illuminated Clarity grading. This results in missing a lot of face up internal graining and often results in twinning being given lower grades than expected from a frontal view.

GIA and IBM Research Join Forces to Transform Diamond Grading

CARLSBAD, Calif. – July 27, 2020 – GIA and IBM Research have joined forces to develop an advanced artificial intelligence (AI) system designed to revolutionize diamond clarity grading.

www.gia.edu

 

[MackPUK]

Thanks for the additional insight and further reading material Garry H!