Considering "recut" of OEC to clean up facets

[Aurora26]

Almost all diamond prices are based on the Rappaport Diamond Pricing Guide. There are numerous changes in price/carat at various carat weights. However IIRC there is no break at 2.50ct. All 2.00-2.99ct diamonds have the same $/ct price varying only by color and clarity. For your stone, given you have lots of room above 2.00ct, I think I might be more concerned about maximizing face up size, and getting a fabulous looking diamond rather than staying above 2.50ct.

Of course you would want to keep weight loss to an absolute minimum, but if getting the diamond of your dreams means going below 2.50ct then I think you might want to keep that option in your thoughts.

Lots and lots to think about here! To begin with here's a copy of the 2008 AGS Cut grade proportion chart. I've added some of the cut proportions I know for sure make fabulous OECs. The CER square shows the proportions Victor Canera uses for all his Canera European Rounds. The AVR square shows the proportions of @diamondseeker2006's gorgeous August Vintage Round. The PRS square shows my DWs averaged proportions, and the Aur square shows your current averaged proportions. You can see there's lots of opportunity to improve the cut of your diamond!!!

Oh wow that chart is so helpful. Can I ask what "SL" stands for?

It does seem like for the moderate option, I would land in the higher end of Good, while for the more "ideal" option, I would land in the mid-upper area of Good. It is a personal thing to not want to fall below 2.5ct and also keep that extra tiny bit of diameter but maybe I'll take a couple more days to think about it. I am looking through Love Affair Diamond's smugmug page to see if there's any AGS stones with comparable angles.

 

[prs]

SL stands fort the Sweet Line of ideally proportioned diamond cut proportions as posted in RT by @Serg

 

[Aurora26]

1.94ct Old European Cut Diamond - AGS N, VS2 - loveaffairdiamonds

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loveaffairdiamonds.smugmug.com

2.76ct Transitional Cut Diamond - AGS J, VS2 - loveaffairdiamonds

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loveaffairdiamonds.smugmug.com

These two seem to get us close to the "after" angles. The second isn't as helpful as it veers very much into MRB territory. I don't know.....not sure what to compromise on lol

 

[prs]

Actually in looking again at the cut chart your "moderate" option only improves into Fair territory.

 

[Aurora26]

Actually in looking again at the cut chart your "moderate" option only improves into Fair territory.

Mistype from me! Meant to state “higher end of Fair.”

 

[Karl_K]

Got some info back from the cutter including a Sarine scan of my stone. Measurements are all over the place lol. We are going to proceed with the first more "moderate" option:

2.50ct+
Crown average 37 degrees
Table +-57%
Pavilion average 42 degrees

+-2.40ct
Crown 36 degrees
Table +-55%
Pavilion 41.5 degrees

Any feedback? I am most comfortable with keeping the stone above 2.5ct, so those crown and pavilion angles are the compromise.

1st none of those combos make for an oec its more of what some people call a transitional.

Both combos can work but the star% must be kept very short to keep the upper girdle angle low. 35% or shorter.
This is in keeping with older cuts with larger tables and steep crowns, they were often cut with super short stars for the same reason.
Lowers just outside the table for both combos.

 

[Karl_K]

Using charts intended for mrb is not useful for an oec or "transitional" and is misleading.

Do the pavilion mains drive light return in the modern round brilliant?

Article by Karl K. On many websites you will see it said that the pavilion main facets drive light return. Top labs and many grading systems use the pavilion angle […]

www.pricescope.com

 

[xxxxxx]

I actually really like my cut. Sometimes I would love to change up the numbers and see how a diamond with other measurements would perform (like super small table etc.) but this just is really hard to find so many oec flavors to live with and then compare. It’s just not feasible for me at the moment.
My current diamond is beautiful in my eyes and for me it’s the perfect balance of spread and depth (:

 

[kgizo]

@Karl_K Is this chart still helpful for OECs? Sorry it’s so hard to read, found it here on PS and have not seen a high res version.

 

[Aurora26]

1st none of those combos make for an oec its more of what some people call a transitional.

Both combos can work but the star% must be kept very short to keep the upper girdle angle low. 35% or shorter.
This is in keeping with older cuts with larger tables and steep crowns, they were often cut with super short stars for the same reason.
Lowers just outside the table for both combos.

Is "upper girdle angle" synonymous to crown angle?

@Karl_K Is this chart still helpful for OECs? Sorry it’s so hard to read, found it here on PS and have not seen a high res version.

Huge range for Excellent crown angle (31-3. Not seeing pavilion angle on here at all.

 

[Karl_K]

Is "upper girdle angle" synonymous to crown angle?

no. upper girdles run from the end of the stars to the girdle.

 

[Karl_K]

@Karl_K Is this chart still helpful for OECs? Sorry it’s so hard to read, found it here on PS and have not seen a high res version.

While there are some combos in those ranges that are nice just because it gets EX to VG on that chart does not mean its a good one.
It also mixes GIA OEC and circular brilliant and what some called "transitional" together under OEC.

 

[prs]

Using charts intended for mrb is not useful for an oec or "transitional" and is misleading.

Do the pavilion mains drive light return in the modern round brilliant?

Article by Karl K. On many websites you will see it said that the pavilion main facets drive light return. Top labs and many grading systems use the pavilion angle […]

www.pricescope.com

Karl, I agree the chart I posted is not as accurate for an OEC as it is for an MRB because the difference in the length of the Lower Half Facets will impact light return. I don’t agree it is not useful in helping the OP make her decision. Showing how the cut proportions of her diamond compare to the proportions of OECs we know have great light performance is neither useless or misleading.

You reference your Pavilion Mains article to justify trashing my chart, so in order to learn more I have read and re-read your article. It uses computer generated Ideal-Scope images to compare the light performance of a Morse/Wade OEC with a modern MRB. The OEC has a 40% Table and 60% Lowers, and the MRB has a 56% Table and 80% Lowers. The Crown Angle on both diamonds is set at 35.0°. The Pavilion Angles are then varied until a huge change in light leakage is detected on the images. This is the data point you produced for the MRB.



I compared your data to GIA and AGS cut grade charts to help me learn how I am going wrong with my OEC chart. Here are their charts for MRBs with identical proportions to the one you used. Your PAs of 41.15 and 41.25 would both round to 41.20 on the charts so I’ve highlighted 41.0, 41.2, and 41.4 to make sure I’ve captured the PA where you see that huge jump in leakage.



The problem I’m having is that none of the charts show this huge increase in leakage that you report in your article. I do want to learn how to improve my OEC chart, but I don’t understand why the GIA and AGS charts don’t seem to confirm the data point from your computer generated Ideal-Scope images. Karl, could you please explain all this to me?

 

[Karl_K]

Karl, could you please explain all this to me?

Yes, your missing the entire point of the article, the mains in a modern RB are not the primary cause of under table leakage it is the lower half/girdle angle in relation to the crown angle and table size.
An oec does not have lowers under the table which changes the light performance under the table to 100% the mains.
This changes the possible pavilion angles for the highest light performance in fact it changes it potentualy to the max pavilion halves angle for that combo MRB that provides no leakage at 80% lowers,.

 

[prs]

I assure you I am not missing the entire point of the article. I am fully aware the length of the Lowers will effect light return. The real question is by how much? This is the info we need to determine what adjustments to my OEC chart might be needed to make it more accurate.

You use your computer generated images to claim that, for the OEC, the huge jump in light leakage occurs between PAs of 42.24 and 42.34. So you are essentially saying the optimum PA for an OEC with 60% Lowers is 1.10° higher than an MRB with 80% Lowers. Of course this entire article becomes just a puff of smoke if your computer generated images are not accurate, or your interpretation of them is incorrect.

This is reason the question I asked, and that you have avoided answering, is why the GIA and AGS cut grade charts don't confirm this "huge jump in leakage" you see in your MRB at 41.25°.

 

[Karl_K]

This is reason the question I asked, and that you have avoided answering, is why the GIA and AGS cut grade charts don't confirm this "huge jump in leakage" you see in your MRB at 41.25°.

41.25 is specific to a 56 table and a 35 crown and 80% lowers it varies when they change.
AGS charts are not fine grained enough to show it clearly and gia gross rounding is a huge joke at this level.

 

[prs]

FYI Octonus have a page on their website that concisely summarizes all these various cut charts and lists them by table size LINK They have an updated 2007 version of the AGS chart vs your 2004 version above.

AGS and GIA will round both your 41.15 and 41.25 to 41.20. That's why I highlighted 41.0, 41.2, and 41.4. If there is a huge jump in leakage the labs would surely have picked it up over that range. So you still haven't answered my question.

 

[Karl_K]

AGS and GIA will round both your 41.15 and 41.25 to 41.20. That's why I highlighted 41.0, 41.2, and 41.4. If there is a huge jump in leakage the labs would surely have picked it up over that range. So you still haven't answered my question.

The proofs are in the article.
GIA gross rounding makes their data useless for looking at this level.
The AGS charts are do not go into small enough detail.
Neither AGS nor GIA make a grading system or charts for other designs that works for oec, or "transition" cuts and they do not claim that they do so.

 

[Karl_K]

Taklking about the mrb, Here is the pgs1.1.2 chart for 56% table there is a jump from 0 at 41 degrees to 2 at 41.2
Something happened in that range hmmmm wonder what...

 

[yssie]

@prs.

Here we go again.

To begin with here's a copy of the 2008 AGS Cut grade proportion chart. I've added some of the cut proportions I know for sure make fabulous OECs. The CER square shows the proportions Victor Canera uses for all his Canera European Rounds.

Victor Canera's stones most certainly don't all fall into this range. No idea where you got this generalization from, but it's provably inaccurate.
Also this chart is specific to a 53% table and 55% star.
50/38.1/40.7/51 CER: https://www.victorcanera.com/diamonds/8NTM43/1.012ct-G-VS2-old-european-cut-natural-diamond

AGS and GIA will round both your 41.15 and 41.25 to 41.20. That's why I highlighted 41.0, 41.2, and 41.4. If there is a huge jump in leakage the labs would surely have picked it up over that range. So you still haven't answered my question.

It's well known that GIA has high tolerance for light escape under the table ("leakage"), so the fact that GIA's charts don't adjust their cut grade to reflect increased light escape is wholly unsurprising. AGS Gold cut evaluation serves largely the same agenda as GIA's cut grade so once again, wholly unsurprising. This leaves the third chart as the only one of any consequence to this line of questioning.

However, your understanding of AGS' rounding scheme is incorrect. Pavilion angle was rounded to the nearest tenth of a degree using the half round up method. 41.14 would have become 41.1, 41.15 became 41.2, 41.24 became 41.2, and 41.25 became 41.3. The values that @Karl_K used, then, would have been rounded to 41.2 and 41.3. But chart doesn't account for single-degree pavilion gradient.

So where, in a chart that increments by 0.2 degrees, should these poor chart publishers have chosen to cut the 0 grade off? Many 41.1s will be blood red under the IS, but some won't. Some 41.2s will be blood red under the US, but many won't. By cutting 0 off at 41.0 they knew that folks who ignored AGS usage recommendations and took the charts as gospel (which, by the way, is what you're doing right here, over a decade later) would toss some babies out with the bathwater. If they'd extended their 0 grade to 41.2, they'd have included too many stones that (AGS felt) really ought to have been graded lower.

I suppose one could consider it unfortunate that @Karl_K chose 41.15 and 41.25 rather than 41.15 and 41.24, as his pictures would have demonstrated identical "huge jump in leakage" wholly within the rounded 41.2 box, per your presumption. For those who did notice, though, I can't speak for him but I'm going to guess that he didn't expect to encounter someone misguided enough to try to turn a 0.01degree differential into a strawman, and explaining the choice in the article would have demanded a long and completely-unrelated tangent.

@Karl_K is explicitly making the point that thanks to rounding the charts aren't fine-grained enough to pick up on precisely where these cliffs will occur. The charts validate his assertion. Your OEC chart is similarly not fine-grained enough to pick up on precisely where cliffs will occur, even if there was some magical world wherein all four axes of a round could be finished to identical proportions.

 

[prs]

@prs.

Here we go again.


Victor Canera's stones most certainly don't all fall into this range. No idea where you got this generalization from, but it's provably inaccurate.
Also this chart is specific to a 53% table and 55% star.
50/38.1/40.7/51 CER: https://www.victorcanera.com/diamonds/8NTM43/1.012ct-G-VS2-old-european-cut-natural-diamond

Hey @yssie, great you could chime in, your input is always welcome. Thanks for diving into Victor's inventory and spotting the one CER that didn't fall into my stated 37.0, 40.8 range. The good news is you've given me another data point to add to my chart. I already had a bunch of AVR data points, so I added them too.



I find it both interesting and informative the two foremost OEC cut experts in the USA have chosen to set their OEC Pavilion angles somewhere around 0.6° to 0.8° higher than the corresponding MRB ideal cut angle. I think this certainly provides some guidance to the OP as she makes her recut decisions. For sure it will point her in the right direction.

I assume you and Karl have already noticed this relationship, so I really don't understand why you think the chart is useless and without meaning. If either of you have a better chart, please post it.

 

[yssie]

Hey @yssie, great you could chime in, your input is always welcome. Thanks for diving into Victor's inventory and spotting the one CER that didn't fall into my stated 37.0, 40.8 range. The good news is you've given me another data point to add to my chart. I already had a bunch of AVR data points, so I added them too.



I find it both interesting and informative the two foremost OEC cut experts in the USA have chosen to set their OEC Pavilion angles somewhere around 0.6° to 0.8° higher than the corresponding MRB ideal cut angle. I think this certainly provides some guidance to the OP as she makes her recut decisions. For sure it will point her in the right direction.

I assume you and Karl have already noticed this relationship, so I really don't understand why you think the chart is useless and without meaning. If either of you have a better chart, please post it.

The point that we’re all trying to make is that you can’t choose OECs by charts. And you can’t dictate recuts using charts.

You also can’t choose or dictate recuts for modern pear brilliants, modern non-branded oval brilliants, modern non-branded cushions, modern non-branded radiants, modern non-branded step cuts, modern marquises, old pears, old ovals, old non-branded style cushions, old non-branded style step cuts, old marquises, trillions, half-moons, rose cuts, briolettes... And the myriad other fancy shapes I’m missing...

A pavilion angle change by itself is meaningless. A pavilion angle change combined with adjusted lower halves, adjusted upper halves, adjusted stars, and adjusted table - now you’re starting to tell a story. The person planning and doing the recut knows this story much better than any end consumer.

That CER was second stone in current inventory that I looked at, no diving required. Your labeling of squares is entirely missing the point, but if wish to continue to populate your cache against all advice you might take the time to at least ensure you’ve populated it accurately before pronouncing it fact.

 

[Karl_K]

@prs you asked why the pavilions can be steeper on an oec its has 2 parts:
The pavilion angle is not limited by the lower halves leaking like with a mrb.
The second is obstruction, a super-ideal cut has pavilion mains that go dark in some viewing conditions(arrows).
It is a small part of the diamond so it provides contrast.
.
However the oec mains showing the same darkness will make the entire under table area dark.
In fact a lot of old oec's were cut that way and are better in pendants, earrings, and crowns with the greater viewing distance.
So depending on the exact combo of table%, crown angle, upper girdle angle, and lower halves %/angle it often but not always needs to be steeper to provide less reaction to obstruction.

 

[maita13]

@Aurora26 , may I ask if you proceeded to recut your stone?
Curious to see results of your recut.

 

[Aurora26]

@Aurora26 , may I ask if you proceeded to recut your stone?
Curious to see results of your recut.

Yes I did and happy to provide some updates! Working with Ashley was great and his pricing (by ct) / timeline (1 month exactly from first email to receiving the final set ring back) was very reasonable. My stone is now more of a transitional style that is very fiery and very bright edge-to-edge.

Final results:

 

[Sprinkles&Stones]

Yes I did and happy to provide some updates! Working with Ashley was great and his pricing (by ct) / timeline (1 month exactly from first email to receiving the final set ring back) was very reasonable. My stone is now more of a transitional style that is very fiery and very bright edge-to-edge.

Final results:

Wow that’s incredible!!! I love the fact patterns!

 

[tyty333]

Looks beautiful!

 

[maita13]

That stone IS amazing, @Aurora26 !! The facet pattern is indeed stunning, and I’m very pleased for you! Please start a thread. I’m sure there’s quite a few of us who’d love to see pics and videos of this stunner

 

[Cerulean]

Id love to see more pictures or videos! I have a messy MRB I hope to recut and I have a soft spot for transitionals