Strange Idealscope Result

[minhon]

I have been looking at this JA 3Ex diamond which it's proportion should not deviate from the ideal cut a lot.

https://www.jamesallen.com/loose-di...-color-vvs2-clarity-excellent-cut-sku-3275390

However, when I see the idealscope it seems there are plenty areas of light leakage....and the shape of the arrows are not normal...

And the HCA score si 4.0... (i first time see the score for 3Ex diamond)

Why would this happen...?? what's wrong with it? The table and depth should be ok...

 

[Karl_K]

57/35.5/41 with gia gross rounding which in this case was likely down based on the idealscope. The real angles are likely over that.

When it comes to diamonds a very small change in angle can make a big difference.

I agree with the hca score for this one.

 

[flyingpig]

This idealscope result is expected and consistent with the HCA score, the 360 video and the proportions.

 

[diamondseeker2006]

We tell people to stick with HCA scores of under 2. The idealscope image you posted is the reason why we recommend under 2. GIA Excellent is a very broad category and many are not what we'd consider to be excellent. That's the whole reason for using HCA.


These are measurements to help you stay in ideal cut territory with a GIA excellent cut stone.

table: 54-58
depth: 60-62.3
crown angle: 34-35.0 (up to 35.5 crown angle can sometimes work with a 40.6 pav angle)
pavilion angle: 40.6-40.9 (sometimes 41.0 if the crown angle is close to 34)

 

[minhon]

So just under 2.0 would be safe? even some margin case like 1.9 or just 2.0? Based on your experience, is it rare that there would be a good diamond that is higher than 2.0?

Also, my fd bought a diamond with HCA 2.7. I thought it would have some problem, but when he received it , it seems still being sparkle, really don't know what is the problem, maybe the diamond might be underperforming in some scenario.

https://www.jamesallen.com/loose-di...h-color-vs2-clarity-excellent-cut-sku-2676191

We tell people to stick with HCA scores of under 2. The idealscope image you posted is the reason why we recommend under 2. GIA Excellent is a very broad category and many are not what we'd consider to be excellent. That's the whole reason for using HCA.


These are measurements to help you stay in ideal cut territory with a GIA excellent cut stone.

table: 54-58
depth: 60-62.3
crown angle: 34-35.0 (up to 35.5 crown angle can sometimes work with a 40.6 pav angle)
pavilion angle: 40.6-40.9 (sometimes 41.0 if the crown angle is close to 34)

 

[Karl_K]

Also, my fd bought a diamond with HCA 2.7. I thought it would have some problem, but when he received it , it seems still being sparkle, really don't know what is the problem, maybe the diamond might be underperforming in some scenario.

https://www.jamesallen.com/loose-di...h-color-vs2-clarity-excellent-cut-sku-2676191

That combo can be ok, depending on the actual angles and specifics of the cut.
Others not so much, so in that case hca errors on the safe side.
Just at a glance that one appears to be towards the safe side so I would not expect glaring issues.

For example ags grade for such a combo could range from ags0 to ags2+

 

[newjourney]

So just under 2.0 would be safe? even some margin case like 1.9 or just 2.0? Based on your experience, is it rare that there would be a good diamond that is higher than 2.0?

Don't treat the HCA numbers as absolute because lower is not necessarily better. Yes, there have been diamonds discussed here that is higher than 2.0, yet still perform well. Diamond performance is not black and white. Small changes in each of the diamond proportion result in different positioning/angle placement of the virtual mirrors. HCA is a decent tool to narrow down the playing field. But it's just a tool. I don't see it holding any more weight than other tools like IS/ASET/video when making online purchase. HCA can often contradict the others since it makes certain theoretical assumptions. Moreover, in the instances when AGS light tracing certification has been done, HCA becomes less useful.