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OEC Ideal Cut?

Karl_K

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@prs and @Karl_K no worries to analyse my stone.
ok , 1st I assume you know that the girdle has been 95% probability reworked it would have had a much thinner girdle originally.
So @prs that is the first question model it as is or with a thinner girdle?
 

prs

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ok , 1st I assume you know that the girdle has been 95% probability reworked it would have had a much thinner girdle originally.
So @prs that is the first question model it as is or with a thinner girdle?
No it didn't occur to me the girdle might have been reworked, but IIRC Al Gilbertson's book did say that most old cuts had extremely thin or even no girdle at all. So if it got chipped over the years it makes sense it could have been reworked to remove the chips.

By subtraction the girdle calculates out at 4.7%, and that doesn't exactly match up with the cert description as "Medium to Slightly Thick". I suppose its quite possible a lab out of Antwerp may not use the GIA definition. I measure the culet at 7% and its description as "Very Large" also doesn't match the GIA definition.

Karl, I bow to your expertise to do what's best. I'm thinking that to use the data from the cert we have to model it as is, and assume the cert data is OK. I checked the table and it measures out at exactly 50%, so that's a sign the data is good.
 

Karl_K

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ok will work on it, later tonight or tomorrow sometime.
 

Karl_K

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Ok im starting to think that using someones diamond is a mistake.
I'm not getting it to be super close(can't duplicate variations in the real diamond without a full scan on a high end scanner at the best settings) and I'm starting to see why they fell to the wayside. I am not comfortable talking about that when discussing someones diamond.
@prs give me some starting numbers in the B zone.
 

prs

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Ok im starting to think that using someones diamond is a mistake.
I'm not getting it to be super close(can't duplicate variations in the real diamond without a full scan on a high end scanner at the best settings) and I'm starting to see why they fell to the wayside. I am not comfortable talking about that when discussing someones diamond.
@prs give me some starting numbers in the B zone.
Karl, I've been thinking about the best way to do this without consuming too much of your time, but putting Area B to bed for sure one way or another.

Here is a revised chart that shows more of Area B

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

We know that in Area A some CA, PA combinations work better than others, as shown by the AGS cut guide. It would be logical to assume the same thing applies to Area B, and some combinations will work better than others.

In Area A it seems the best combinations are close to Bruce's Black area. I also put in the data point for @Acinom's diamond, and it too is very close to a black area. I'm thinking we pick a particular CA, and then take two PA combinations that are close to the black areas. Finally if things are looking good, and you have time, maybe do a third combination in the middle of the CA vertical.

The Area B CA vertical on the chart highlighted in light blue color is at 32.5°, so the three points would be:
A: 32.5, 38.6
B: 32.5, 36.6
C: 32.5, 37.6

If I were able to choose the facet details, my preference would be 50% Table, 35% Stars, and 65% Lowers. :)

Karl, just my suggestion, I'm totally open if there's a better way to do this.
 

Karl_K

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ok all 3 combos are similar with similar looks and performance all have the same downside. I modeled them with 1% girdles to be more period correct with more modern girdles the issues will be larger.
I posted the middle combo.

prsnumbers.jpg
prsnumbers2.jpg
superideal.jpg
 
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Karl_K

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Here is why 37 just because your a lil crazy that way :}
I tried 35 and there was min performance change.
why37.jpg
prsnumbers3.jpg
 

Karl_K

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The fisheye becomes apparent with some tilt from 2-5 degrees, its minor and I would not mind owning one but its enough to scare off the trade raised on any fisheye is awful.
With a more modern girdle it will be worse in a lot of cases.
 

Karl_K

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This is so interesting! Diamonds = higher maths!
What was surprising is that you get less than a 1 degree or just slightly over depending on who you ask swing in pavilion angles for a modern RB.
Where this combo works pretty much the same over a much wider pavilion angle range.
 

prs

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Here is why 37 just because your a lil crazy that way :}
I tried 35 and there was min performance change.
why37.jpg
prsnumbers3.jpg
Wow, thank you Karl, I was half expecting Area B to be a complete dud. When you said the AGS cut guide didn't properly account for obstruction that's when I went looking for more info, and found Bruce's article.

Is that the Kozibe effect in your image above or am I seeing things?
 

prs

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I'm now feeling as lost as I did in the one college math class I was required to take, so will just look forward to the gorgeous photos when you find this diamond...:)
I have this fantastic image in my OEC file, but I've no idea where it came from. Maybe one of @Karl_K's articles?

This is what we hope DW's OEC will look like!!! :love: :love: :love:

MRB OEC Comparison.jpg
 

Karl_K

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Wow, thank you Karl, I was half expecting Area B to be a complete dud.
I am surprised how well these are working.
I hadn't played with this range before.
around 40 40 is interesting also.
 
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prs

Brilliant_Rock
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This is so interesting! Diamonds = higher maths!
Actually it's basic trigonometry that I learned in grammar school when I was about 12 years old. I think it stuck in my memory because that was long before calculators and computers existed. We had to draw it out on paper and use a book of log and trig tables, together with a slide rule to do the calculations.

I even remember the memory aid; TOA, CAH, SOH, it came in handy when I was trying to measure the crown angle on this profile shot of your magnificent ring. :)

Acinom 1.png

Edit: Of course Karl's analytical program is not just basic trig, it's a heck of a lot more complicated than that!!!
 
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Karl_K

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Ok I played with those new numbers a little, they are extremely twitchy about the upper girdle angle with the upper girdle are showing week light return to mostly leakage. I think there might be some good combos there but they are not going to be cuttable within reason.
Do you want me to play with them some more or move on to a different area?
I am willing to do either.
 

prs

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Ok I played with those new numbers a little, they are extremely twitchy about the upper girdle angle with the upper girdle are showing week light return to mostly leakage. I think there might be some good combos there but they are not going to be cuttable within reason.
Do you want me to play with them some more or move on to a different area?
I am willing to do either.
If that area is too twitchy perhaps we should just move on. Maybe try a CA of 35.0°? This would be interesting in that the crown would be close to ideal, but the PAs would be in another universe. :)

1: 35.0, 38.4
2: 35.0, 37.2
3: 35.0, 36.0
 

Karl_K

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36 is to shallow and 38.4 steep but there looks like a good zone close to 37.2 or a bit over. It is worth playing with.
 
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prs

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I couldn't understand how @Acinom (54.2%), @dreamer_dachsie (55.4%), and @evergreen (56.7%) could have such gorgeous stones when all the cut guides said these shallow stones shouldn't look so good. I'm so glad Area B does exist, thank you again @Karl_K, and helps explain how the master cutters of a hundred years ago knew a thing or two about diamonds!!!

I'm not exactly sure how Area B actually helps DW and I in our search, except it does teach us to keep a sharp eye open for one of these ultra shallow wonder stones!

I think the main point about Area B is it may offer the opportunity for beautiful stones to be cut at much lower depths than currently. Hopefully that might offer some cost savings if appropriately sized rough could be purchased. It would take a lot of design research, but wouldn't it be great if Karl could invent another great diamond design, a very spready transitional OEC! =)2
 

Karl_K

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They went away for the same reason that most diamonds are cut steep deep these days(expensive rough with price based on yield) with a secondary cause of minor to major fish-eye problems that are worse when cut with modern girdles.
MMD eliminates the rough problem.

I am still working on it, its interesting.
 

Karl_K

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What is interesting is Morse/Wade came up with 41 degrees for a 35 degree crown 40%T oec and indeed its good.
 
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Karl_K

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Here you go.. this combo does not work as well with strait line stars but a minor variation works well with a modern girdle.
The score of fish-eye .75 I feel is over harsh.

prs4.jpg
prs4l.jpg
prs4s.jpg
 
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Karl_K

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@prs this is fun so if you want pick another set of numbers.
 

prs

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@prs this is fun so if you want pick another set of numbers.
@Karl_K I'm just shooting in the dark trying to pick combinations that might work, I may have gotten lucky once, but if this is anything like me playing roulette in Vegas I can assure you we are headed for a long losing streak! :mrgreen2:

I would much prefer to rely on your expertise rather than my luck, so my last suggestion is we move another 2.5° to the right on the graph and try a CA of 37.5. So the numbers would be:
4: 37.5, 38.0
5: 37.5, 36.6
6: 37.5, 34.8

I notice for Area B as we move to the right the CA is increasing at three times the rate of the PA. So it may be the CA 37.5 is already past the point of offering a significant carat weight saving. If so it might be better to move back towards the left hand side and try to zero in on the best zone.

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

Karl_K

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@prs modeling the entire range is something im not doing and havent done so your picks are as good as mine. Im interested in the steeper crown also
In mined rough these are not practical hower mmd is another story but this is just for fun but we might learn stuffs.
 

Karl_K

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I used automation to try and narrow it down as I wasn't getting anything that great by hand.
At least with a 50 table the 37.5ca range is a bust.
The pdf file shows the ASET files.
 

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diamondseeker2006

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I think you guys are just having some fun! I think you're doing this the hard way, though!

I am going to have to say that Yoram cut my AVR and I think it is one of the best newly cut OECs. I would guess Karl will agree that Yoram is a master cutter. So I may be totally wasting my time, but I am going to show you my facet pattern, an ASET image, and the numbers from the grading report. Mine does have an advantage of facing up with a nice diameter since it was not cut too deep.

Obviously, there are many others with a different cut, but it seems to me that looking at a variety of newly cut OECs that were cut to have great light performance and have actual images of the stones would be a good way to approach this.

IMG_0838 b.jpg

IMG_0787.JPG

n IMG_0826.jpg
ASET name edited.jpg AVR.AGSreport 2.jpg
 
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