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Help understanding GCAL proportion diagram

diagram.jpg
OK so top to bottom left to right:
0.06mm 1.2% is girdle thickness
3.99mm 61.2% is total depth of the stone
34.0% is crown angle
40.9(?) is pavilion angle
6.52mm is the total diameter
3.52mm is the table measurement
55.5% is the table as a percentage of the total diameter
0.02mm 0.3% is the culet (is this an OEC? MRBs don't usually have culets but I can't see one in the picture)
0.90(8?) mm 15.1% is the crown height as a percentage of total depth
2.8(6?)1mm 43.1% is the pavilion depth as a percentage of total depth
(I can't work out how these are calculated with the values I'm guessing at from the picture and the article below)
This article goes into how everythng is derived https://www.gia.edu/diamond-cut/diamond-cut-anatomy-round-brilliant
Does that help?
 
Last edited:
foxinsox said:
diagram.jpg
OK so top to bottom left to right:
0.06mm 1.2% is girdle thickness
3.99mm 61.2% is total depth of the stone
34.0% is crown angle
40.9(?) is pavilion angle
6.52mm is the total diameter
3.52mm is the table measurement
55.5% is the table as a percentage of the total diameter
0.02mm 0.3% is the culet (is this an OEC? MRBs don't usually have culets but I can't see one in the picture)
0.90(8?) mm 15.1% is the crown height as a percentage of total depth
2.8(6?)1mm 43.1% is the pavilion depth as a percentage of total depth
(I can't work out how these are calculated with the values I'm guessing at from the picture and the article below)
This article goes into how everythng is derived https://www.gia.edu/diamond-cut/diamond-cut-anatomy-round-brilliant
Does that help?
Click to expand...
Great post :appl:
 
Thanks very much!!! I am looking a diamond with this report. I am trying to figure out if it is good diamond. The Table is 68%, the girdle is 2.1%, the total depth is 60%. The crown angle is 16 degrees and the crown is only 4.6% and pavillion 53%. This is a cushion cut. It has a symmetry rating of good and one extra facet on the pavilliion but G Vs2. Any advice on whether this seems like a good stone?
 
You can't really buy cushions / Emerald Cuts / Asschers / fancy cuts in general from the numbers alone - it's all about how the facets interact with each other, so ideally you'd have ASETscope images to confirm head-on light performance and cut accuracy, and video to understand if it 'works' when moving in real life :))

If this is a round, though, IdealScope and ASETscope are used for the same reasons as above - but if it's not a MRB, video is still useful to understand its 'character', especially if it's an OMC or OEC!
 
OoohShiny said:
You can't really buy cushions / Emerald Cuts / Asschers / fancy cuts in general from the numbers alone - it's all about how the facets interact with each other, so ideally you'd have ASETscope images to confirm head-on light performance and cut accuracy, and video to understand if it 'works' when moving in real life :))

If this is a round, though, IdealScope and ASETscope are used for the same reasons as above - but if it's not a MRB, video is still useful to understand its 'character', especially if it's an OMC or OEC!
Click to expand...
OoohShiny said:
You can't really buy cushions / Emerald Cuts / Asschers / fancy cuts in general from the numbers alone - it's all about how the facets interact with each other, so ideally you'd have ASETscope images to confirm head-on light performance and cut accuracy, and video to understand if it 'works' when moving in real life :))

If this is a round, though, IdealScope and ASETscope are used for the same reasons as above - but if it's not a MRB, video is still useful to understand its 'character', especially if it's an OMC or OEC!
Click to expand...
OoohShiny said:
t
Click to expand...

I have seen the stone and the light the GCAL image says excellence brilliance. The thing I was worried about is that the GIA symmetry is only "good" with the extra facet. It is more of a case of liking the stone but being a little worried about the specs. Is good symmetry a red flag? thanks!
 
Hmm...brilliance is not the only way to judge a cushion. A round brilliant is going to be more brilliant than a cushion, so I'd wonder what they mean by it having "excellent" brilliance. Many older cuts increased fire at the expense of brilliance. This sounds like an older stone to me because the symmetry is only "good." As you seem to know, "good" is actually not that good.

As OooohShiny says, you can't judge a cushion by any of this. The master old cutters were quite capable of arranging the facets to get spectacular results, even though they couldn't get the symmetry we see today. Extra facets actually used to be considered a sign of a good cutter. If done right they can increase the size of the cut stone, or remove an inclusion. In any case there are so many different types of cushion that you can't begin to judge it without pictures.
 
This looks like it is a MRB, not a ”fancy shape”.
 
To me a 4.6% crown height is a deal killer in pretty much any stone.
 
Karl_K said:
To me a 4.6% crown height is a deal killer in pretty much any stone.
Click to expand...
This is actually a modfieid cushion brilliant. What is wrong with the 4.6% crown height? Sorry I am new to this and getting engaged. I appreciate everyone's help.
 
diamondjow said:
This is actually a modfieid cushion brilliant. What is wrong with the 4.6% crown height? Sorry I am new to this and getting engaged. I appreciate everyone's help.
Click to expand...
In simple terms,
It limits the light draw from other areas than directly in front of the diamonds table.
It has a negative impact on the life of the stone, How lively it looks as you move it.
 
Karl_K said:
In simple terms,
It limits the light draw from other areas than directly in front of the diamonds table.
It has a negative impact on the life of the stone, How lively it looks as you move it.
Click to expand...

Karl_K, would you say that this stone trades life and sparkle for brilliance? That's how I would interpret it.
 
ChristineRose said:
Karl_K, would you say that this stone trades life and sparkle for brilliance? That's how I would interpret it.
Click to expand...
In theory that might happen, but if someone is willing to compromise crown height to save weight are they going to cut the pavilion to good angles for high brilliance or try to keep as much weight as possible by using what ever angles they can fit?
 
Under 5% is a very flat crown. Flat crown will have a pancake-like appearance from the side, not a muffintop. Light goes into and out of a crown.

If you don’t have much of a crown, you won’t get much light or fire out.
 
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