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Ideal Dimensions for Brilliant Round Diamonds???

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checkoutthehook

Rough_Rock
Joined
Mar 1, 2020
Messages
34
Hi everyone. I was wondering if someone might be able to tell me what the ideal dimensions are for a round brilliant diamond (table, depth, crown and pavilion angles, etc). I’ve read numerous different articles on this and they all seem to say something slightly different. Very confusing. Thanks!
 
Honestly it is a little confusing because the various proportions all work together in relation to one another.

Also you have to consider there is averaging and rounding that occurs in the numbers we see on the lab report. Then the actual precision faceting (or lack thereof) that the stone exhibits has an effect as well.

But generally speaking this will help you narrow the field considerably.
  • 54-57 table
  • 60-62.5 depth (prefer <62)
  • 34-35 crown (maybe 35.5 if paired with 40.6 pavilion)
  • 40.6-40.9 pavilion (maybe 41, if paired with 34 crown)
  • 75-80 lower girdle facets (LGF's)
  • Inverse relationship between crown & pavilion, meaning steep crown/shallow pavilion or vice versa (35/40.6, 34/40.9, 34.5/40.8, etc)
  • The above should yield you a stone with HCA of 2 or less, but still run an HCA and check it. Prefer 1-2 for e-rings.
  • If you have advanced images, they trump the HCA as they confirm actual performance vs the HCA guesstimated performance
Using an ASET and/or idealscope (IS) image will help provide confirmation of light performance. Hearts and arrow (H&A) images will help determine symmetry. Not many vendors offer any these advanced images. And even fewer offer all them. However, they provide assurance of the stones quality. Alternatively, you could buy your own scopes if shopping locally or from an internet vendor that doesn't offer the images. You just need to be prepared to possibly return and start over if something is off.

Hope this helps!
 
OMG thank you! This information was very helpful. I did get a HCA score of 2.3. But I also ordered an Ideal Scope as well. Thanks again!!!!
 
Glad it helped!

As you probably noticed a score up to 2.5 can be okay if symmetry and faceting are precise.

Definitely wise to get the scope, so you can confirm.
 
The diamond that I am looking at has ideal proportions according to your list EXCEPT for a depth of 62.7 and a crown angle of 36.5. Those fall outside of ideal but it may still perform very well visually. I just don’t know yet. The diamond has a cut, polish and symmetry of excellent according to the GIA report. So we’ll see I guess.
 
See it in person to check what you make of it. PS is very skewed towards ‘superideals’ but realistically consumers will find many stones thar don’t fit the bill stunning.
 
MsShnooks said:
See it in person to check what you make of it. PS is very skewed towards ‘superideals’ but realistically consumers will find many stones thar don’t fit the bill stunning.
Click to expand...
This! I don’t have an ideal stone at all by PS standards but I love my ER and am proud to wear it everyday. Try not to get too caught up in the numbers game. Really look at the diamond, examine it in all types of lighting situations. Thankfully you have a 30day return policy. So take your time checking out the stone’s personality. Also, buy a cheapie UV light off of Amazon. I think your stone has SF if I’m not mistaken from your previous thread. Plus it’s cool to see the stone with direct sunlight (icy blue hue) and then use the UV light in a darker room. It’s neat!
 
Great! Thank you! Yeah I plan to get as many opinions as possible on this diamond, both here and in person (including an independent appraisal). I confess that I have been getting caught up in the numbers aspect. Maybe I shouldn’t be. Maybe I can relax a little if an independent assessment comes back positive and the diamond performs really well visually.
 
I would agree the numbers don't always tell the whole story. A month or so back I created a post where "by the numbers" the stone looked great. But it was a complete nightmare. This is why symmetry and faceting matter. More importantly why images, video and advanced images do make a difference.

Why Advanced Images Matter...A Bad 34.5/40.8...

I'm just as guilty as anyone. Helping someone find a stone and run across one with that 34.5/40.8 combo. You smile. You then run through the rest of the proportions.... 57 table, 61.7 depth, 75 LGF's, 50 stars and medium-slightly thick girdle....check, check, check,check and check You...
www.pricescope.com

With that said, the purpose of staying within a set of ideal proportions is to minimize buying risk and help pinpoint you to a stone that has higher odds of working.

That's not to say the stone you picked, or anyone else picked, that doesn't align with the suggestions above isn't "good enough". Only the person viewing can determine that. I don't even have all your proportions but I can tell you the 36.5 crown is contributing to the overly steep 62.7 depth.

Also, because the stone is a little deep it's carrying extra carat weight in that vertical plane, meaning it doesn't have as large as a spread (diameter) as a stone with ideal proportions. So your stone will look a little smaller for it's carat weight than a stone of equal carat weight with more ideal proportions.

Hopefully the 36.5 crown is paired with a 40.6 pavilion. And hopefully the actual pavilion values stay at 40.5 or better and don't go too high. Just as I hope the actual crown values hover around 36.5 as the max but have actuals that are slightly less. Of course without a detailed SARIN report you won't know this information, but if something doesn't work it will show up in the idealscope.

When you get the stone and your scope, I hope you are able to take some pictures and post back. I'd like to see the image. There is a possibility you will have some leakage.
 
Okay thanks. The crown is 36.5 as noted and indeed the pavilion is 40.6. If that helps appearance any.
 
Can you post a copy of the report, or give us all the proportions on it. That would help.
 
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