What’s the best proportions and angles?

[alab]

I’ve seen DejaWiz recommend these ranges

• ⁠PA 40.6-40.9°
• ⁠CA 34-35° (35.5° max for PA of 40.6°)
• ⁠Crown Height 15.0-15.5% (14.5% min, 16% max)
• ⁠Table Width 54-57% (max of 58%)
• ⁠Overall Depth 60.5-62.5% (closest to 61%)
• ⁠LGF 75-80%
• ⁠Star Facets 50-55%

And Kim N recommend
Crown angle 34-35
Pavilion angle 40.6-40.9
Depth 60.4-62.4
Table 55-58

What’s the best source?

 

[0515vision]

They're essentially the same. In addition to hitting optimal angles, you need a well-cut diamond free of graining, strain, tinge, painting & digging, twist, etc. That's only going to be determined by seeing the actual stone.

Both @Kim N and @DejaWiz find wonderful diamonds. I wouldn't sweat the 0.1% here or there. There are too many variables when searching for a stone.

 

[Kim N]

 

[AdaBeta27]

I’ve seen DejaWiz recommend these ranges

• ⁠PA 40.6-40.9°
• ⁠CA 34-35° (35.5° max for PA of 40.6°)
• ⁠Crown Height 15.0-15.5% (14.5% min, 16% max)
• ⁠Table Width 54-57% (max of 58%)
• ⁠Overall Depth 60.5-62.5% (closest to 61%)
• ⁠LGF 75-80%
• ⁠Star Facets 50-55%

And Kim N recommend
Crown angle 34-35
Pavilion angle 40.6-40.9
Depth 60.4-62.4
Table 55-58

What’s the best source?

Those are from the old Pricescope "cheat sheet." And Todd Gray of NiceIce.com was a major force behind that set of parameters. Table size is an individual preference, at least for modern round brilliants. I happen to like 55-56% with a decent crown height, for fire. A larger table, say 60%, with a shallower depth like 60% is a "60/60" diamond and those are going to have more brilliance (white light) than fire.

What are the perfect diamond proportions?

In general people say that the overall geometry is responsible for the optical performance. So there is a range of proportions that would be classified as ideal, but what is the exact proportions to make the most brilliant diamond. If you assume absolute precision in cutting, there must be an...

www.pricescope.com

Preferred specs "cheat sheet" (for rounds)

I have a friend who is starting to look around at stones and I wanted to give her the "cheat sheet" for rounds but I can''t find it (senility at 37 is a terrible thing... ) Depth Table Crown and pavillion angles Etc... Thank you!

www.pricescope.com

Pricescope has also discussed what PS refers to as FIC firey ideal cut (more fire, deeper, faces up smaller), BIC brilliant ideal cut (more white light, could be shallower and spready), and TIC Tolkovsky ideal cut (intended to provide a good balance between fire and brilliance). You can search those terms if interested. Some limited info is in this thread: https://www.pricescope.com/community/threads/so-if-i-prefer-a-brighter-whiter-diamond….280141/#post-5279260
eta: So many lab RBs are cut with a 58% table that I wager finding a FIC lab stone ready-made is doubtful, and you'd probably have to buy an ordinary stone and have it specially recut.

 

[DejaWiz]

 

[lovedogs]

Those recommendations are the same and come from PS

 

[0-0-0]

IMO optical symmetry matters more than the differences between those ranges.

 

[Karl_K]

1......2......3 Kim wins!!!!!

Both ranges are a subset of possible well cut proportions and include a few that are mildly steep deep and leave out some great ones.