shape
carat
color
clarity

What Is the Best Proportions For 60/60 BIC As A Pendant?

John_Z

Rough_Rock
Joined
May 6, 2021
Messages
1
Hello Guys,

I am planning buy a pendant for my wife. I barely remembered the words from a 2013 essay "people no longer create head shadow on diamond when they look at a pendant horizontally. How much light the diamond reflect is more important than fire and scintillation for pendant. A shallower crown angle diamond is better for pendant." IS this theory still works? and how much shallower is best? Does anyone knows the exact CA、 PA、table% and depth% that shows the greatest brilliance for a Pendant diamond?:confused:

I compared two 60:60 diamonds.
(1)The first diamond is Carat:2.15 Depth60.1 Table 59 Crown32 Pavilion 41.2 and Meaurements of 8.35*8.39*5.03, which gives a HCA score of 1.9-Excellent-within BIC range that has Very Good in light return, Fire and Scintillation and Excellent in Spread.
(2)The second diamond is Carat:2.29 Depth60.2 Table 59 Crown33 Pavilion 41 and Meaurements of 8.5*8.56*5.13, which gives a HCA score of 1.0-Excellent-within TIC range that has Excellent in all four evalution criterions.
Which diamond is better for a necklace?

@Garry H (Cut Nut) please help :boohoo:


Thanks a lot,
Z
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
5,127
Remember, the HCA is an approximation tool. It doesn't consider minor facets, nor does it account for GIA gross rounding. Those variables can change things considerably. For these reasons I would prefer stone 2 of your options.

IMO, the HCA is overly generous to shallow stones and I think others have noted that as well.

Either way, Garry provided an updated PS proportions chart in this thread that may help shed a little light on your situation. Essentially as you move away from the green area, you are sacrificing either fire and/or white light return and also spread and risk of chipping.

As I mentioned earlier, the HCA ignores the minor facets and @Karl_K wrote an article explaining why lower girdle facets (LGF) mater so greatly. Effectively the crown angle, pavilion angle and table size work in unison with the LGF % to create an LGF angle. When that angle exceeds 42.24 degrees, the LGF's begin to leak.

I went into a little more detail on this with a thread where Karl and I was discussing this. I am still wanting to do the math & create a spreadsheet where you can enter select proportion values and calculate the LGF angle. I have not completed that yet. I do know that the diamond software calculates this if you enter the variables into it but unfortunately I don't have access to that program.

My point being, I am concerned that depending on the LGF % of stone 1 that the proportions may exceed that critical 42.24 LGF angle and cause problems.

Both Karl & Garry are trade and have more knowledge than I do. So they may be able to better explain and/or confirm a few things here as well.

1599808248669.png
 

Karl_K

Super_Ideal_Rock
Premium
Joined
Aug 4, 2008
Messages
11,390
@sledge the exact angle for the lowers to cause issue varies with the crown angle and a little with table size.
I have a few other things going on right now that Im not working on it.
The problem is that the leakage had to be judged by simulated IS images and its very hard to get each one close enough to the others in having the same leakage to get meaningful data to create a table.

Which MRB would I use in a pendant?
My first pick would be a gia vg cut with a shallow pavilion(40.2,40.4 gia)and a table around 55 and 34+ crown angle with reasonable face up optical symmetry and reasonable girdle that scores under 2 on the hca.
Go big with the money saved on the VG cut grade.
They are pretty rare however and have limited upgrade potential.

Second MRB pick would be an all around cut like a super-ideal or other well cut stones.

60/60s work well in pendants but they would be down my list.
 
Last edited:

Karl_K

Super_Ideal_Rock
Premium
Joined
Aug 4, 2008
Messages
11,390
@sledge
Table 59 Crown32 Pavilion 41.2: there is no reasonable lower angle that will cause a leakage issue.
Table 59 Crown 33 Pavilion 41: same thing.
That assumes no twist.
I was not aware of that.
If you increase the pavilion angle to 41.8 mains you can get steep enough lowers in a reasonable mrb range to make an issue.
Interesting.
 
Be a part of the community It's free, join today!
    The Jewelry of Disney's Cruella
    The Jewelry of Disney's Cruella
    He Said, "Yes!"
    He Said, "Yes!"
    Father's Day Jewelry: 2021
    Father's Day Jewelry: 2021

Need expert help finding that diamonds?

Holloway Cut Advisor



Diamond Eye Candy

Click to view full-size image.
Top