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OEC Ideal Cut?

evergreen

Brilliant_Rock
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Jan 18, 2012
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513
By the way -- I would 100% love it if someone wanted to cut some stones like @dreamer_dachsie / @arkieb1 / mine: these shallow, biggish-tabled, chubby-arrowed trannies. I have an AVR, and it is objectively a beautiful stone, but somehow the performance is not such a love-of-my-life like this 1.30ct. AVRs are floral, these stones are checkerboardy and that's the performance I love. Arkie did a rundown of this sort of stone (at least, I think it's appropriate to lump them, although she specifically differentiates hers from Dreamer's!) in her post introducing Charlie.

...unlike Dreamers stone which is no secret I have coveted forever, this one has a much bigger table and fatter arrows than JJCs stone. I actually asked poor Erica a zillion times if it had the arrows in real life because many trannys show contrast patterns with them in some photos, but in person you cannot see them at all in real life. This one shows them in low lighting and is a chunky checkerboardy blaze of fire the rest of the time. It's the best of both worlds I think. Dreamers is a early American cut or a type of OEC both her stone and Dems stones have much smaller tables, this is tranny with really really fat arrows, if I had a choice I would pick this style of stone with a smaller table but they are difficult to find over 2 carats so it's a matter of taking what you can get;

trannies.jpg
Dreamer has already confirmed that her stone is one of these shallow/biggish table, and Arkie mentioned hers has a big table though I don't see its depth reported anywhere. @arkieb1 , @dreamer_dachsie -- do the numbers we're talking about here sound like your stones? Shallow, largeish table, mid-range (65%ish) lower halves? What about Coati's 2.94ct M-N?

It is definitely a different flavor from the AVRs/CERs of the world and I don't think it's been adequately described/investigated. IMHO. Because I want to buy a BIG ONE when I grow up. :lol:
 

prs

Brilliant_Rock
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Here again is the modified AGS cut chart superimposed with the Bruce Harding diamond faceting chart, but this time I've added my three OEC data points in pink.

AGS Cut Guide 10mm MRB 50% Table Rev D.png

I became more of a believer in Bruce's area B when I realized where @dreamer_dachsie's stone fell. I estimated her CA and PA from a great profile photo posted in one of her threads. Maybe her diamond really was cut by a genius working outside the box. :)

I still have no idea if Bruce Harding's chart might be useful. @Garry H (Cut Nut) made the original reference to that article, and I believe he had a lot of respect for Bruce. I am hoping that Garry might stop by and let us know if Bruce's chart for Diamond might be accurate, and if I am using it correctly.
 
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evergreen

Brilliant_Rock
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Jan 18, 2012
Messages
513
I became more of a believer in Bruce's area B when I realized where @dreamer_dachsie's stone fell. I estimated her CA and PA from a great profile photo posted in one of her threads. Maybe her diamond really was cut by a genius working outside the box. :)
C'mon, Area B!! :D Who wants to simulate the perfect Area B stone for us (and who wants to cut it)?? :dance:
 

prs

Brilliant_Rock
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BTW, some obstruction is good/necessary, but too much is "bad". This is too much :shock: : https://www.jamesallen.com/loose-di...m-color-vs2-clarity-excellent-cut-sku-6385670 (but, y'know, since it's a 13mm diamond I wouldn't kick it out of bed for eating crackers.). You can/should imagine that, when looking directly at that diamond, it's going to reflect a lot of your face and not the ambient light.

I thought a lot about obstruction when looking for an emerald cut, since there are only like 15 virtual facets to think about. :lol: Contrast these four:
1594932110790.png
Just going VERY quickly through JA's inventory, here are 4 different-looking cuts. The first might have too much obstruction to be awesome, but then again, I just told you that obstruction is important for patterned flashing so it might be OK (I ultimately selected an emerald cut diamond from JA which looked a little over-obstructed in this view and I have no regrets!). B has a big ol' window with a lousy cut. C looks to me to have a good combination of obstruction and light return. And D lacks contrast -- to my eye, it needs *more* obstruction to give the patterned scintillation I expect. HTH. :)

link that might work to try to play with all 4 in their rotating view.
@evergreen if this wasn't difficult enough, I'm not only looking for the ideal OEC cut, but thanks to you I'm now looking for the ideal cut with the perfect amount of obstruction. :eek-2:

Thank you so much for the education, you do know that sometimes ignorance is bliss? :lol-2:
 

prs

Brilliant_Rock
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C'mon, Area B!! :D Who wants to simulate the perfect Area B stone for us (and who wants to cut it)?? :dance:
It looks like Area B might be a No-Go area for the trade. :mrgreen2:

I was about to give up on it, but I think I might have found another outlier. @Acinom has a collection of colored stones second to none, and I just discovered she also has an absolutely fabulous 5.3ct OEC with a depth of only 54.2%.. My preliminary cut estimate puts in squarely in Area B, but I'm hoping to see a GIA to help confirm. Here'a a LINK to her JOTW thread, it's in SMTB and I have given it a bump.
 
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Moonie

Shiny_Rock
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Mar 10, 2020
Messages
190
In order to figure out the flower petal pattern under the table, I started off again using the average OEC table of 50%, and with varying lower half facet lengths to see how they looked.

OEC Fig 10A T50,50,50 S35,35,35 L55,60,65.jpg

GIA have an OEC cut criteria that lower half lengths should be less than or equal to 60%, so I was amazed that a length of 55% did not produce petals, and they just began to show at 60%. The pattern began to look pretty good at 65%, so I experimented with even longer lengths.

OEC Fig 10B T50,50,50 S35,35,35 L70,68,65.jpg

70% didn't look quite right to me, although 68% looked good. DW preferred the 65% so that's what counts of course. I went thru the same exercise with other table sizes and this is how I ended up.

OEC Fig 13 T45,50,53 S30,35,40 L70,65,63.jpg

Once the flower petals are in place it becomes easier to see the effect table size has on the look of the overall pattern. They all look really beautiful, but I think I like the 45% and 50% table over the 53%, however I'd take any of them if the facet pattern is right. DW has a preference for the 50% table, so now I know what I'm looking for! =)2

Next up is what are the ideal Crown and Pavilion angles to go with these facet patterns.
This is such a fascinating thread! I've been trying to follow because I would also love to know what combinations cause the beautiful bubbly flowery OECs. Does ""lowers" in this case mean the overall depth? I unfortunately only have depth and table in my GIA so I don't know any of the other numbers :/
 

prs

Brilliant_Rock
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"Lowers" are the Lower Half facets, also known as the Lower Girdle facets. Their length is very important in OECs as it determines the shape of the flower petal pattern under the table. In the first two diagrams above you will see the table is constant at 50%, and the only difference between the six examples is the length of the Lowers, and the corresponding change in the facet pattern under the table. In the third diagram the size of the table changes, and the Stars and Lowers have to change accordingly to maintain a similar pattern.

Here's an image showing what all the different facets are called.

Facet Diagram 2.png

GIA do not provide cut details for OECs or Circular Brilliants, so the purpose of these diagrams was to help me look at a diamond and recognize the facet pattern. Hopefully this will work for you too. :)
 

Moonie

Shiny_Rock
Joined
Mar 10, 2020
Messages
190
"Lowers" are the Lower Half facets, also known as the Lower Girdle facets. Their length is very important in OECs as it determines the shape of the flower petal pattern under the table. In the first two diagrams above you will see the table is constant at 50%, and the only difference between the six examples is the length of the Lowers, and the corresponding change in the facet pattern under the table. In the third diagram the size of the table changes, and the Stars and Lowers have to change accordingly to maintain a similar pattern.

Here's an image showing what all the different facets are called.

Facet Diagram 2.png

GIA do not provide cut details for OECs or Circular Brilliants, so the purpose of these diagrams was to help me look at a diamond and recognize the facet pattern. Hopefully this will work for you too. :)
**frantically takes notes :D** I really wish I had more information about my diamond because I'm so curious about the performance. I can't wait to see what you and your wife pick out!!
 
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prs

Brilliant_Rock
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Screenshot_20200727-172149.png
Screenshot_20200727-172127.png

This L VS1 came up in my feed on IG and I thought of you. I inquired for the GIA cert and better pic (above). It's $45k ish.
http://instagr.am/p/CDH8e0hBKbK/
Wow, thank you so much for thinking of me!

It is indeed a very interesting stone, with a lovely facet pattern and a huge spread. In the video there's maybe a little obstruction under the table. The main issue in the video is it definitely faces up yellow, much yellower than @joelly's recently acquired fantabulous L.

I'm thinking the very shallow cut doesn't have the right proportions to give good light return, and there's not enough reflected light to dilute the yellow. DW wants a warm stone, but this one is a little too warm. We know for sure shallow cuts can be gorgeous, and face up great, but this one isn't quite doing it for us.

@CHRISTY-DANIELLE I feel guilty now for criticizing the diamond after you have gone to so much trouble. I hope you don't mind, I do very much appreciate you keeping a look out for me! :)
 

Karl_K

Super_Ideal_Rock
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@prs pick some area b numbers table% ca and pa and post them. I need some rooom on both sides to play so dont pick ones on the very edges.
 

Karl_K

Super_Ideal_Rock
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In the video there's maybe a little obstruction under the table.
of course there is but not all at once and for the huge amount of over obstruction it is very near perfection for the cut when it comes to responding to obstruction.
 

prs

Brilliant_Rock
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of course there is but not all at once and for the huge amount of over obstruction it is very near perfection for the cut when it comes to responding to obstruction.
Karl, could you please explain what you mean by "the huge amount of over obstruction". I have never heard that term before.
 

prs

Brilliant_Rock
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I
@prs do you actually prefer AVRs or CERs more? ;-) not an easy decision for me!
CERs are all cut to exactly the same proportions, and I definitely prefer his longer lower halves that produce a gorgeous flower petal pattern under the table. The only thing I don't like is he doesn't align his star facets with the table.

Looking at the AVR certs I see a lot more variation in the proportions. All fall within great AGS cut grades so that's really not an issue. However to me, his lowers are often not quite long enough and you only see the flower pattern when the stone is tilted.

@Lessics I remember your thread on re-cutting an MRB into an OEC. This might not be as difficult as we first thought, please stay tuned. =)2
 
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prs

Brilliant_Rock
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@prs pick some area b numbers table% ca and pa and post them. I need some rooom on both sides to play so dont pick ones on the very edges.
Thank you Karl! Here's one I just discovered that blew my mind. It's @Acinom's fabulous 5.3ct OEC that won JOTW back in 2013. here's a LINK to that thread. The diamond is definitely an outlier, and sits squarely in Area B. Here are a couple of photos of the diamond, and a copy of the cert. The table is 50.5%, and I calculate the CA at 28.5° and the PA at 37.8°.

Acinom 2.png Acinom 3A.png Screenshot (613).png
 

Karl_K

Super_Ideal_Rock
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@prs we can only discuss someones stone with permission and are more limited than just made up numbers.
 

prs

Brilliant_Rock
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@prs we can only discuss someones stone with permission and are more limited than just made up numbers.
I agree, I can sometimes get ahead of myself. :eek-2: Let's wait awhile to see if @Acinom gives us the OK to proceed.

It would be great to analyse a diamond we know is a great performer, but If she prefers not to, then no problem, I'll pick a CA, PA at random.
 

Karl_K

Super_Ideal_Rock
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Karl, could you please explain what you mean by "the huge amount of over obstruction". I have never heard that term before.
Normal obstruction is your face as you look at the diamond and varies a very large amount by distance.
AGSL uses 25cm or ~10 inches for ASET.
Garry uses as I recall 12 inches for IS.
Over obstruction is when a greater amount of obstruction than that is applied.
Black camera and lens from a few inches makes for a huge amount of over obstruction compared to a human viewing it.
 

prs

Brilliant_Rock
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This one's got quite a bit of leakage under the table. You can see it in the video.
I presume it might be this leakage that makes the diamond look more yellow.

@ForteKitty I would love to know how you spotted it in the video, could you please tell us what it is you look for.
 

prs

Brilliant_Rock
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Normal obstruction is your face as you look at the diamond and varies a very large amount by distance.
AGSL uses 25cm or ~10 inches for ASET.
Garry uses as I recall 12 inches for IS.
Over obstruction is when a greater amount of obstruction than that is applied.
Black camera and lens from a few inches makes for a huge amount of over obstruction compared to a human viewing it.
Thank you, I thought you might mean the huge prongs were causing over obstruction! :mrgreen2:
 

ForteKitty

Ideal_Rock
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I presume it might be this leakage that makes the diamond look more yellow.

@ForteKitty I would love to know how you spotted it in the video, could you please tell us what it is you look for.
I can see it. You can literally see through the area under the table as it's moving around, I don't know how else to explain it.
 

prs

Brilliant_Rock
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I can see it. You can literally see through the area under the table as it's moving around, I don't know how else to explain it.
Thank you, yes I see what you mean. I believe I can even see the outline of the tweezers holding the ring! The facets move with the stone, but the stuff beneath the diamond doesn't.

The music accompanying the video was OK the first couple of times thru, but after that it started to drive me out of my mind!!! :mrgreen2:
 

prs

Brilliant_Rock
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@prs do you actually prefer AVRs or CERs more? ;-) not an easy decision for me!
CERs are all cut to exactly the same proportions, and I definitely prefer his longer lower halves that produce a gorgeous flower petal pattern under the table. The only thing I don't like is he doesn't align his star facets with the table.

Looking at the AVR certs I see a lot more variation in the proportions. All fall within great AGS cut grades so that's really not an issue. However to me, his lowers are often not quite long enough and you only see the flower pattern when the stone is tilted.

@Lessics I remember your thread on re-cutting an MRB into an OEC. This might not be as difficult as we first thought, please stay tuned. =)2
@Lessics One thing I forgot to mention in my reply is I think CERs exhibit the Kozibe effect. I am definitely not an expert, but I believe I can spot the culet reflections in his videos.
 
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