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Diamond Question (Crown vs. Pavilion Angle)

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Barcode88

Rough_Rock
Joined
Dec 12, 2018
Messages
5
Hi everyone,

First time poster but long-time lurker. I think I have a good handle on carat / clarity / color but I am hearing alot of mixed things about cut. I've been evaluating a 3.5ct diamond that grades well on the other metrics but seems to show poorly on the Holloway score (5+) with metrics being:

Depth: 62.2
Table: 58
Crown: 35
Pavilion: 41.4

Does it really hurt the brilliance of the diamond that much? It's hard for me to get a sense because I don't have an eye for this stuff and it's hard to tell based on a picture.

Thanks for the help
 
PS forgot to mention it is a "round brilliant" diamond
 
Barcode88 said:
Hi everyone,

First time poster but long-time lurker. I think I have a good handle on carat / clarity / color but I am hearing alot of mixed things about cut. I've been evaluating a 3.5ct diamond that grades well on the other metrics but seems to show poorly on the Holloway score (5+) with metrics being:

Depth: 62.2
Table: 58
Crown: 35
Pavilion: 41.4

Does it really hurt the brilliance of the diamond that much? It's hard for me to get a sense because I don't have an eye for this stuff and it's hard to tell based on a picture.

Thanks for the help
Click to expand...

The Pavilion angle is too steep at 41.4 which is why it scored poorly on the HCA. Pair that with a 35 Crown Angle there will be light leakage. Ideal parameters for a Crown Angle 34 to 35 and for Pavillion Angle 40.6 to 40.9
Most people on this site also prefer a table between 54 to 57.

With a steeper crown angle you want to pair that with a shallow Pavilion Angle like 40.6 for best performance. And with a steep Pavillion Angle like 40.9 you want to pair that with a shallow Crown Angle like 34 for best performance. Hope this helps.
 
You can find better. What are the specs you are looking for?
 
Check out one of the pages under the Knowledge tab at the top of the forum:

https://www.pricescope.com/wiki/diamonds/diamond-cut

As per the graphic on it, it will appear leaky/see-through (because the angles don't complement each other and light exits the stone out the side rather than back out the top) and also small (because the angles mean light is not being reflected from edge-to-edge, making the edges look dark, and also because the steep crown / deep pavilion is 'hiding' weight, so the 'spread' (diameter) will be smaller than a stone cut properly).

using_IS_Reference_Chart_72.jpg
 
If you are happy to post your budget and your requirements/preferences in terms of the colour/clarity/carat size, we can help find you something much better, as Stephan has said :))
 
This helps alot. Thanks everyone. Sounds like I need to keep looking for something closer to:

Crown: 34 / 35
Pavilion: 40.6 - 40.9
Table: 54 - 57

I'm not too fussed about the other stuff, just focused on bigger carat and good cut. Thinking F/G color and VS1/2
 
Barcode88 said:
This helps alot. Thanks everyone. Sounds like I need to keep looking for something closer to:

Crown: 34 / 35
Pavilion: 40.6 - 40.9
Table: 54 - 57

I'm not too fussed about the other stuff, just focused on bigger carat and good cut. Thinking F/G color and VS1/2
Click to expand...

We can help you find something what is your budget?
 
Finding stones with ideal proportions that are complimentary to each other is the key.

Using AGS charts, you can see the proportions of this stone land precisely as very good (VG) with about 67% probability to remain VG and 33% to creep into excellent (EX) territory depending on cut quality.

I'm sure the stone is labeled a GIA XXX stone, but hopefully you can see "excellent" doesn't always mean excellent when shopping GIA stones. You have to analyze the data to confirm.

Capture.PNG
 
Think I found something a little bit closer to what you guys were guiding to, that is a 36 Crown and a 40.6 Pavilion on a 57 table. It scored below 2 on HSA. I could probably buy an Idealscope but I don't really know what I'd be looking for. Do you think given it checks the box on GIA and HSA that'd be sufficient? I've seen many diamonds in store and I couldn't really tell the difference between a 5HSA and 2HSA but I don't have a discerning eye for this kind of stuff so really appreciate everyone's help on this. My budget is pretty flexible and really focused on just finding the right rock but I've been looking in the 3-4ct range with good specs
 
Unfortunately it's not always enough to be GIA XXX and HCA below 2. It's helpful to get an ASET or IS images from vendors to confirm light performance. We are happy to help if you give us your approx budget.
 
@sledge, was there any response from the mods about linking to a google sheets version of your cut spreadsheet/cheat sheet?
 
bmfang said:
@sledge, was there any response from the mods about linking to a google sheets version of your cut spreadsheet/cheat sheet?
Click to expand...

Yes -- unfortunately it was not a favorable one. I was asked to refrain from sharing any links and also limit the use of screen captures on this forum. :(2
 
Yes, cut, proportions, angles, faceting make a huge difference in the appearance of a diamond, but also in the value of the diamond. The best cutting ensures that incoming light is bounced around the interior of the diamond in the most efficient manner so none of that light is lost. The more effectively the light is reflected internally, and the less allowed to escape, the more impressive the brightness, fire, sparkle, and life of the diamond will be. Now, what does that mean for shoppers?

1. It is important to remember that whatever crown angle appears on a report is actually eight different numbers that are getting averaged. Same with the pavilion angle. So, lab reports are insufficient to capture the precision the best cutters are able to achieve.

2. Also, lab diamond scanners have a published error of ±0.1 degrees angular in every instance.

3. Every facet and facet group on a perfectly cut diamond is calibrated with precision against the others and is reliant on the others. Clearly, you are learning to appreciate that a table angle of X has implications for pavilion angle Y (etc). But the labs don’t report every set of numbers, those they do report are averages and those averages are subject to that scan-error.

4. For example, the upper girdle facet specifications are not represented on the report at all. They’re critical to the makeup of the crown as a whole, and the details of upper girdles, bezels, stars and table considered together determine much about compound mirror integrity, and need to be balanced precisely against the makeup of the pavilion on each stone individually.

5. This doesn’t happen by accident. Quite the contrary, it takes an extraordinary time effort and skill to calibrate the diamond’s performance in 3D while taking into account the alignment of all 58 facets. Rather than just an an averaged set of data points on a lab report-- which is what most cutters do.

6. You are probably thinking: what about AGS0 light performance-- surely that captures it all, right? No. Light performance is a range. Within the AGS0 grade there are diamonds that are better and worse in terms of light return. And the lab’s quantification of performance is still limited in that it doesn’t quantify the amount of light one AGS0 exhibits against another. All the AGS0 measures is that the diamond has met a minimum threshold for light return. But from there--- it’s silent. It doesn’t measure how much better than the minimum for an 0 a diamond has.

7. Now, you are probably asking: what about the ASET scope image? Surely that is an excellent evaluation tool that will help me compare diamonds for performance and will make up for the deficiencies of the lab report? And you are correct it does correct some of the deficiencies, but even ASETs can’t do it all. The scope gives a motionless view, but the benefits of precision-cut brightness and contrast pattern integrity occur over a full range of tilt. Technical diamond analysis is best performed in-person with full depth perception. 2D photos can be unreliable (1) because any off-axis between lens, diamond or stage creates skewed patterns. (2) inconsistencies in girdle plane or lighting can create false reflections and artifacts. (3) over-produced photos dull and dilute details.

So what does that mean? If you want the best value for your budget, you need it all. Step by step. Basic numbers on a lab report are a starting point. Not an ending point.
 
@sledge Is there a way to get access to your excel sheet? I wanted to plug in the metrics of the diamond I am considering: 36 Crown angle, 40.6 Pavilion angle on a 57 table.
 
Barcode88 said:
@sledge Is there a way to get access to your excel sheet? I wanted to plug in the metrics of the diamond I am considering: 36 Crown angle, 40.6 Pavilion angle on a 57 table.
Click to expand...

My diamond has those specs. Scores 6 cells in Ideal, 3 in Excellent if I recall correctly. I believe @sledge created his spreadsheets based on the spreadsheets that used to be available on the AGS website (not sure if they are still available). FWIW, I’m thrilled with the performance of my diamond, but I’m also one who cannot see much if any difference between a diamond branded Super Ideal vs. one with near Super Ideal specs (certainly not a difference enough to pay the 20%-30% premium for a Suler Ideal). If you feel you might be sensitive those differences and/or prefer to pay the premium for the assurances that Super Ideals provide, it may be worth your time and efforts to see the difference side by side before you decide. GL!
 
Barcode88 said:
@sledge Is there a way to get access to your excel sheet? I wanted to plug in the metrics of the diamond I am considering: 36 Crown angle, 40.6 Pavilion angle on a 57 table.
Click to expand...

I'm willing to share but have been asked by the PS mods to not do so. See post #15 above.


Kaycee2018 said:
My diamond has those specs. Scores 6 cells in Ideal, 3 in Excellent if I recall correctly. I believe @sledge created his spreadsheets based on the spreadsheets that used to be available on the AGS website (not sure if they are still available). FWIW, I’m thrilled with the performance of my diamond, but I’m also one who cannot see much if any difference between a diamond branded Super Ideal vs. one with near Super Ideal specs (certainly not a difference enough to pay the 20%-30% premium for a Suler Ideal). If you feel you might be sensitive those differences and/or prefer to pay the premium for the assurances that Super Ideals provide, it may be worth your time and efforts to see the difference side by side before you decide. GL!
Click to expand...

Good memory @Kaycee2018. ;)2

I would like to echo @LaylaR's comments earlier, but paraphrased -- a beautiful stone is compromised by more than a set of rounded & averaged data points we see on a report. At the same time, those numbers do have meaning as they will have to fall within a certain range to get the desired end result.

While static advanced imagery (idealscope, ASET and H&A) may not capture all movements, it gives us a good representation of what to expect and if there are problem areas.

I'm a car guy so I will try to analyze this in those terms:
  • Looking at word terms like "excellent" from GIA is the equivalent of saying you want a sports car. The range is very wide. I'd be fairly disappointed to get a Mazda Miata when I was expecting a Challenger Hellcat.
  • Encompassing "excellent" but putting in proportion parameters and looking at HCA scores is similar to saying I want a stick shift, 600+ horsepower, 550+ lbs/torque, etc. Guess what? The Miata is out, lol. Now you will get back some results like Corvette Z06, Camaro ZL1, Challenger Hellcat Redeye, Challenger Demon, Bentley Continental GT, Bentley Bentayga, Bugatti Chiron, Cadillac CTS-V and several Ferrari's.
  • Now we're talking. Yet the price and performance varies considerably in all these cars. So we start looking at detailed specifications and really understanding what makes each car special. This is similar to looking at those static advanced images. When we are done we have a good feel for what should meet our performance expectations and budget constraints.
  • Lastly, we see the diamond and can experience how all those factors either come together, or they don't. Same deal with the cars. We do some test drives to get an experience and feel of each vehicle. Years back I remember thinking a Nissan GT 370z was going to be my next vehicle. The sad reality is I'm a big guy and when driving I had to cock my head to the side to as there wasn't enough head room for me to be in a normal vertical position. The sales guy asked if I was sure and of course I was, and proceeded to take him on the test drive of his life. :lol: Needless to say, I wasn't a buyer. But the point remains, when we see and experience things in person sometimes it just all comes together, or in the case of the Z it doesn't come together and you keep looking.
You're going to be spending a considerable amount of money on a stone of the size and specifications you've indicated. I'd encourage you to learn as much as possible so you can understand the various steps of the process. If you want an easy button solution with great light performance, I'd highly recommend you consider someone like WF, HPD, BGD or VC for your purchase. All offer super ideal diamonds and have top notch customer service.

You seem less concerned about the budget and more about the quality of the stone, so I think each of those guys will shine for you. Also, they have good upgrade programs. WF and HPD probably have the best upgrade programs. Although given the size, maybe an upgrade isn't a necessity. It is still a nice contingency. Remember also, upgrading from a 1 carat to 2 carat stone is different than upgrading from a 3-4 carat stone to larger. Inventory supplies will be different, so pick a vendor with ample supply or that can do custom cuts in that size range if that aspect is important.

As requested...here is a screen cap of the chart. Keep in mind, this chart is limited by all the factors I noted above. You need some advanced images, etc to ensure this initial glimpse is a good deal. Right off the bat, the crown is a little high, especially considering GIA rounds & averages values. If the actual individual values go lower that's good, but if they creep higher then that isn't so good.


upload_2018-12-14_11-55-50.png
 
Barcode88 said:
@sledge Is there a way to get access to your excel sheet? I wanted to plug in the metrics of the diamond I am considering: 36 Crown angle, 40.6 Pavilion angle on a 57 table.
Click to expand...

I haven’t found the interactive spreadsheet (yet, lol), but I am able to find charts with google search. Here’s one for a 57% table:

6A04CB56-C184-48B2-9D38-138651867045.gif
 
sledge said:
I'm a car guy so I will try to analyze this in those terms:
  • Looking at word terms like "excellent" from GIA is the equivalent of saying you want a sports car. The range is very wide. I'd be fairly disappointed to get a Mazda Miata when I was expecting a Challenger Hellcat.
  • Encompassing "excellent" but putting in proportion parameters and looking at HCA scores is similar to saying I want a stick shift, 600+ horsepower, 550+ lbs/torque, etc. Guess what? The Miata is out, lol. Now you will get back some results like Corvette Z06, Camaro ZL1, Challenger Hellcat Redeye, Challenger Demon, Bentley Continental GT, Bentley Bentayga, Bugatti Chiron, Cadillac CTS-V and several Ferrari's.
Click to expand...

Have you driven a Miata? (on twisty roads?) If not, you need to, as they are great fun :)

And if you're a bit insane, dislike having tread on your tyres or being able to go round corners, and like to feel like you could die in a fiery crash at any moment, you can ask Flying Miata to drop an LS1 engine in... lol :lol:
 
sledge said:
You're not going to find the interactive spreadsheet, as I custom built it.

FYI, here is a copy of the original AGS proportions chart. You used to be able to find by Google search but it currently gives me a 404 error.

https://www.dropbox.com/s/udzu59blvntvc2c/AGSLProportionCharts.pdf?dl=0
Click to expand...

Ha! I was wondering if you made it or not ... I think I can too, with the help of the file you shared!

And taking the opportunity to say: Thank you, sledge ... I’ve learned so much, and continue to learn so much, from your thorough and thoughtful posts!
 
Last edited:
Sledge, since you are a car guy you might appreciate this analogy:

Let’s pretend that in 1975, the automotive industry decided the “ideal” vehicle would have four doors, a 5.0 Liter, 350 cubic inch engine, safety glass, and driver’s and passenger side airbags. That would mean that in 2018 someone could manufacture a car that fit all of those criteria, but in addition had better gas mileage, side curtain airbags, a modern fuel injection system, power seats (and whatever else you might want), that would still be classified as an ideal vehicle right next to a vehicle with the base criteria from 1975. But one is clearly the winner, despite both having the ‘ideal’ designation. But they are graded the same by the industry. Why? Because the diagnostic criteria is decades out of date.

Just as with that fictional car report, the labs are still using criteria from decades past without any update to account for the technological advances in diamond cutting and planning. Or taking measures to quantify the precision of the facet alignment and its relationship to light return. Just like the automotive industry, diamond cutting has advanced to the point where there is much more that can be done to improve performance. Nowhere on either the AGS report does it mention faceting. It doesn’t require that the faceting on the crown mirrors the faceting on the pavilion in a certain way to optimize fire and sparkle. It doesn’t require that any of the facets be angled a certain way at all, which is odd because faceting is easily the most important criteria that determines a diamond’s performance. The report also doesn’t quantify the quality or the amount light return at all.

Which is why even an AGS0 is not enough if you want the most spectacular diamond for your money.
 
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