I'm confused - diamond depth

[BlondeVenus]

I recently lost my engagement ring and have just had it replaced. Everywhere I've looked, it says my new diamond proportions are too deep (checked so many different sites including the HCA tool).

What I'm confused about, is that the new diamond is more sparkly than the original one (seems to have more scintillation and fire), although the old diamond proportions came up much better with the HCA tool. I know it only matters what I think (not what proportions say) but I'm still confused as to why the diamond does look so sparkly although too deep. The arrows seem fairly well defined. Can anyone help?

Also - how can I determine which percentage of excellent cuts my diamond falls in? I've heard jewellers say GIA keep broadening excellent cut parameters and to look for the tip 5% of excellent cuts. How can you know if it's in the top 5%?

NEW diamond
1.66, E, SI2, GIA certified triple excellent
Table: 57%
Crown Angle: 35.5 (15.5%)
Pavilion Angle: 41 (43.5%)
Depth: 62.9
Girdle: 4% T-STH
7.5-7.54 x 4.73
Most of the inclusions are twinning wisps

OLD diamond
1.4, G, SI2, GIA certified triple excellent - I'm learning that triple excellent isn't all it's cut out to be!)
Table: 60%
Crown Angle: 33.5 (13.5%)
Pavilion Angle: 41 (43.5%)
Depth: 60.7
Girdle: 4% T- STH
7.2-7.24 x 4.38
Most of the inclusions were twinning wisps also


Thanks! I'm interested in learning more as I'm finding I'm quite fascinated with everything about diamonds.

 

[diamondseeker2006]

Can you still exchange this diamond? It is a little awkward for us to give honest advice when it is too late!

Here are the parameters we usually recommend to get one of the best GIA Excellent cut stones:

table: 54-58

depth: 60-62.3

crown angle: 34-35.0

pavilion angle: 40.6-41.0

Your new stone is too deep, and that makes it face up smaller in diameter than it should. I have a 1.65 ct diamond that faces up at 7.6mm. The crown and pavilion angle may result in some leakage and not be as good for light return as it could. That stone scores a 4.0 on the HCA, so it would not be one we'd recommend. We generally recommend stones that score 2.0 or less (sometimes a little over 2 is okay).

Your original diamond had better numbers even though outside our target specs. I suspect the new one looks better at this moment just because it is brand new and very clean. Even though I clean my diamond often, it only looks like new when it goes in the ultrasonic!

 

[John P]

Your original diamond is a 60-60 make, meaning table and depth both near 60%. This category of round brilliant is often very bright but has less visible fire, compared to well-cut ideal/Tolkowsky makes.

Your new diamond is more like an ideal/Tolkowsky make with some added depth. What you see as better "sparkle" is attributable to more perceived fire in its qualities (for certain) and potentially better cutting precision; that last is speculation, but it's based on your comments about well-defined arrows and increased scintillation.

For what it's worth, your original diamond is a candidate for AGS 0 performance. Your new diamond's proportions lie on a threshold where it could be anywhere from AGS1-AGS4 in performance, depending on specifics. Since GIA rounds the report numbers, and that calculation depends on cut-consistency and 3D precision, we cannot know. But your preference for its qualities is a good endorsement.

Everywhere I've looked, it says my new diamond proportions are too deep

They say that because the steep-ish angles create a bit of added weight within the diamond. A well-cut diamond with that spread would normally weigh about 1.55-1.60 carats. Yours weighs 1.66. That does not hinder its performance, it simply faces up a bit small. No problem if you don't mind, it looks good to you and the edges don't go dark in low lighting conditions.

What I'm confused about, is that the new diamond is more sparkly than the original one (seems to have more scintillation and fire), although the old diamond proportions came up much better with the HCA tool. I know it only matters what I think (not what proportions say) but I'm still confused as to why the diamond does look so sparkly although too deep. The arrows seem fairly well defined.

Explained in the first paragraphs above.

Also - how can I determine which percentage of excellent cuts my diamond falls in? I've heard jewellers say GIA keep broadening excellent cut parameters and to look for the tip 5% of excellent cuts. How can you know if it's in the top 5%?

GIA has not "broadened" the EX parameters. With time and enlightenment more and more jewelers are coming to realize there's a vast range of EX that has never been very excellent. There are some guidelines here and there which can help narrow the field, but even averaged report data cannot tell the whole story of a diamond's cut-quality. Images can also help, especially scientific reflectors like ASET, but to fully understand what's inside the numbers the diamond must be seen in-person.

Thanks! I'm interested in learning more as I'm finding I'm quite fascinated with everything about diamonds.

So am I! I hope the above is interesting and helpful.

 

[John P]

Hi DS. I was composing my post as you posted yours.

Your new stone is too deep, and that makes it face up smaller in diameter than it should. I have a 1.65 ct diamond that faces up at 7.6mm. The crown and pavilion angle may result in some leakage and not be as good for light return as it could. That stone scores a 4.0 on the HCA, so it would not be one we'd recommend. We generally recommend stones that score 2.0 or less (sometimes a little over 2 is okay)

If GIA's rounding is on the deep side the HCA score could come down under 3.0. Cut-consistency can also help with such diamonds. With that said, it does carry extra depth.

BlondeVenus: If you're really interested, it may be fun to take the new diamond and compare it with a known performer such as Hearts On Fire and see how you think it holds up.

 

[diamondseeker2006]

I wish you had posted first since your replies are always technically 100% deeper than mine, John! Without ASET images or more precise grading, all we have to go by are those numbers provided. Usually 2.0 and less on the HCA results in good performance even with rounding. I am not one to like buying by a GIA report only (even with "good" numbers), so I usually would have an ASET or idealscope at the very least to confirm the light return of stones. Bottom line, I'd rather have a 1.5 ct within ideal cut range than a 1.6 that is not, if there is an opportunity to exchange.

 

[BlondeVenus]

Wow John. Awesome response. Thank you very much! Thank you to everyone else too.
I can't exchange the diamond and I am happy with it ( very happy with the fire, scintillation and I can definitely notice a difference in the colour- it's much whiter) so I'll try and stop researching information that may disappoint me. I was mostly curious as to why it was so much better than the fist diamond.

Thanks to the diamond community