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Help! Do these proportions work?

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Hi guys, I’m looking at a round brilliant, 0.71ct E VS1 with the following proportions:

Table: 55%
Depth: 61.6%
Crown: 35.2 deg
Pavilion: 40.4 deg
Dimensions: 5.72x5.75x3.53mm

The pavilion angle worries me - I know the advice here on PS is to try not to go below 40.6... I have unfortunately also run out of my 3 tries for free HCA scores so I have no idea how this stone is.

I have tried using the online diamond cut estimator too and this stone seems to fall into the AGS Ideal range but not GIA excellent.

Any thoughts and advice on whether these proportions would work are most appreciated!!
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
5,127
Scores 0.7 HCA with excellent in all categories.

Screen Shot 2021-05-17 at 12.32.52 AM.png

The bigger issue is it's not about ONE proportion, but rather the combination of ALL them working in harmony. I'd rather see a steeper crown with the 40.4 pavilion to provide a better inverse relationship between the crown & pavilion. Perhaps a 36 or so. The small table would work, but your lower girdle facets will also come into play. Despite liking fat arrows (numerically smaller LGF's), I think 80 LGF's would work nicer.

Below is a sketch from Garry's (father of HCA & idealscope) website that shows how when you maintain those inverse relationships you can mimic similar light paths.

1621230547855.png

While the HCA is good for getting us "in the ballpark", it fails to account for the minor facets and doesn't really account for cut precision and/or GIA gross rounding which can push actual values < or > than the reported values on the lab report.

Speaking of GIA, the proportions of this stone don't align with GIA. Crowns are reported to the nearest 1%. So it would be 35 as opposed to 35.2. By chance, does it have an AGS lab report? Or is it IGI?
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Thank you so much @sledge!! It is an IGI stone, hence why I am even more wary... it’s hard to find well cut stones with the jeweller I’m with... I’ve been coming across many pavilion angles below 40.4 so I thought this might be a good option. I guess another question would be - would this be terribly different from a stone with 40.1/34.6 sort of proportions? I know it’s hard to compare but just trying to get an idea since this isn’t a super ideal either.
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
5,127
Thank you so much @sledge!! It is an IGI stone, hence why I am even more wary... it’s hard to find well cut stones with the jeweller I’m with... I’ve been coming across many pavilion angles below 40.4 so I thought this might be a good option. I guess another question would be - would this be terribly different from a stone with 40.1/34.6 sort of proportions? I know it’s hard to compare but just trying to get an idea since this isn’t a super ideal either.

I personally would not purchase a stone with 34.6c/40.1p. That is killing the inverse relationship and falls out of all recommended territory by quite a bit, even when ignoring minor facets, GIA gross rounding, etc.

I also would not purchase or recommend an IGI graded stone. My reasoning is simple. The purpose of a lab report is to provide confidence regarding the properties of a diamond. Coincidentally the grades on the reports are used to determine market value for a stone. It is known that IGI can be "soft" on their grading, meaning their report may show a D-VS1, but if it were graded by GIA or AGS, it may yield a G-SI1.

Knowing this erodes my confidence. Also, it introduces (unnecessary) risk that I may overpay for a diamond that is graded soft. I'm not ever going to be okay with either of those scenarios.

Screen Shot 2021-05-17 at 1.09.29 AM.png
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Unfortunately the IGI report doesn’t give measurements of the LGH/LGL :/ and yes I do agree that IGI doesn’t quite inspire confidence the way AGS and GIA do. I have a photo of the stone, but I’m not sure that’s of much help? It’s a family jeweller unfortunately so we’d have to stick to them, but they seem to carry so many IGI stones so I’m just trying as best as possible to find one with okay proportions ><

3648471C-D090-41D3-99CA-AF7B6BC6ED50.jpeg
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Hmm @sledge I found one with a higher crown angle, it’s a 0.76ct E VS1. Apologies it’s once again IGI...
Table: 56%
Depth: 61.6%
Crown: 35.9 deg
Pavilion: 40.4 deg
Dimensions: 5.84 - 5.87 x 3.60 mm

Would this be a better choice? Once again any inputs e.g. HCA are really really appreciated!

What worries me though is that in the photo the arrows look really fat and black compared to the 0.71ct. Should this be a concern? Thanks so much for sharing your expertise!

35505904-2377-42B9-B1F2-49EC9B1863A7.jpeg
 

Dancing Fire

Super_Ideal_Rock
Premium
Joined
Apr 3, 2004
Messages
33,188
It’s a family jeweller unfortunately so we’d have to stick to them, but they seem to carry so many IGI stones so I’m just trying as best as possible to find one with okay proportions ><
Why??, ask them to show you GIA or AGS stones.
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
5,127
Hmm @sledge I found one with a higher crown angle, it’s a 0.76ct E VS1. Apologies it’s once again IGI...
Table: 56%
Depth: 61.6%
Crown: 35.9 deg
Pavilion: 40.4 deg
Dimensions: 5.84 - 5.87 x 3.60 mm

Would this be a better choice? Once again any inputs e.g. HCA are really really appreciated!

What worries me though is that in the photo the arrows look really fat and black compared to the 0.71ct. Should this be a concern? Thanks so much for sharing your expertise!

35505904-2377-42B9-B1F2-49EC9B1863A7.jpeg

The arrows look fat because they have a numerically lower LGF. My guess is these are 75-76ish. The others look like they might be 78-79ish. Those are just a guess and not gospel.

While considered “minor facets” the LGF’s can make or break a stone.

So not only did crown change, but so did LGF. The symmetry is also worse on this stone. You have some pretty obvious misalignment of the arrows in the 6-7 o’clock regions. Ultimately I don’t like this stone any better, and actually less because of the asymmetry.

I’m with @Dancing Fire, I don’t understand why you have to use this jeweler. It seems simple. They need to not only meet cut but also provide reputable grading from GIA or AGS. If not, they aren’t helping you but rather they are hindering you.
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Thank you @Dancing Fire @sledge, really appreciate it. It's a family jeweller so it's a bit hard to say I'd rather go with someone else... :/ I've spent the past couple of hours doing some reading on PS and I definitely see where you're coming from.

However, if I may, could I ask if this 0.76 one would be considered a FIC? I understand that the LGF is lower as well but what would be the result of such a combination? Would the stone appear dark?

I apologise for the many questions but I do sort of feel I'm forced into a corner here with this jeweller so I'd just like to make the best of my situation...
 

tyty333

Super_Ideal_Rock
Premium
Joined
Dec 17, 2008
Messages
23,823
HCA run...ignore that blue line I accidentally drew!
Capture.PNG
Capture.PNG
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Oh thank you @tyty333!! That's..... interesting. I've never seen the HCA say 'within FIC range' but it's probably because of high crown angle. I suppose my question to the experts here would be - I get that it's far from a super ideal/ACA sort of stone, but... will it look acceptable in a ring? Or will it look dark/unimpressive?
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Yeah I do see where you are coming from @lovedogs sigh I really wish they carried better stones than this...

I must admit I am curious though, I’ve seen old posts on here which I think @Karl_K contributed to as well on potential FIC combinations. I am definitely very clueless about all these but the proportions looked really similar to me off the bat, a shallow pavilion and a steeper crown. But is there something about these stones that just make them different? Despite the second one getting 0.8 within FIC range?

I am not ignoring your concerns by any means, these questions are just my curiosity at work! Or is it because it’s an IGI graded (it’s the US IGI lab if it helps) stone so there is no trust that what is on the cert is even true and the proportions might not be the numbers given?

I am really quite stuck and going by the PS proportions of 54-57 table, 59-62 depth these were really the best I could find that were not something shocking like 40.1 pavilion so I’m really in a pinch and just wondering how bad these will turn out ><
 
Last edited:

whitewave

Super_Ideal_Rock
Premium
Joined
Feb 29, 2012
Messages
11,145
Sorry, drinking coffee now so I may have missed it...

have you seen it in person?
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
I know this is not ideal but I have not unfortunately @whitewave. Due to the covid situation we are on lockdown, so we were hoping to decide by the numbers >< Sigh truly my apologies to all of you this is such a non ideal situation but I’m just trying to make the best of it...
 
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Karl_K

Super_Ideal_Rock
Premium
Joined
Aug 4, 2008
Messages
11,392
Anything with a pavilion under 40.5 (~40.45) is going to have some obstruction issues, the only way I consider them in rings is 85%+ lower girdles.

The .71 video above is the wrong stone it should look more like the .76. The stone is the .71 video has a much shallower crown and steeper pavilion than:
Table: 55%
Depth: 61.6%
Crown: 35.2 deg
Pavilion: 40.4 deg
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Hmm that’s strange... it’s definitely the video they provided of that stone though.

Would the obstruction be significant since it’s still relatively close to the border at 40.4 with a high crown to compensate? Or since the arrows are chunky (for the 0.76ct), it’s likely to do badly since the lower girdle is quite possibly shorter? (Thanks @sledge for this info, I wasn’t aware!)
 

sledge

Ideal_Rock
Premium
Joined
Apr 23, 2018
Messages
5,127
Hmm that’s strange... it’s definitely the video they provided of that stone though.

Would the obstruction be significant since it’s still relatively close to the border at 40.4 with a high crown to compensate? Or since the arrows are chunky (for the 0.76ct), it’s likely to do badly since the lower girdle is quite possibly shorter? (Thanks @sledge for this info, I wasn’t aware!)

Chunky arrows indicate a numerically lower LGF. Based on my prior post I guessed at a 75-76ish LGF for the 0.76 stone. This means the LGF’s are too short for this particular combo. @Karl_K is stating an 85 LGF is needed to compensate for the obstruction associated with 40.4 pavilion. An 85 LGF will have a much skinnier arrow than either of your 2 previous photos.

So no, the “fatter arrows” aren’t going to fix the obstruction issue.

I might add we are totally ignoring the fact there are 8 actual crown & 8 actual pavilion values. Those are averaged down to a single value on the lab report. When you say “so close” the average feels close to you but some of the actual pavilions could be even lower. Even small changes of 0.10 in pavilion can alter things greatly.

But mostly it needs to be understood that ONE value doesn’t define good or bad. It’s a combination of all the proportions working together that either does or doesn’t work.
 

chamois

Shiny_Rock
Joined
Jul 15, 2008
Messages
484
I would ask your family jeweller to offer you a choice of AGS & GIA graded stones too. They have more to gain by doing this in my mind!
Good luck:)
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Thanks everyone, let me have a chat with my family and see if they could possibly be open to switching jewellers... I will be completely honest that this is very unfamiliar ground for me and that I was also shown a 34.6/40.1 60-60 stone in the store a while back. Will the stones above be any better in your opinion or is it likely to pretty much look the same? Just looking for some sort of comparison point to wrap my head around this. Thank you!
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
Also out of curiosity... I came across a 33.3/41.3 stone, with 59.5% table and 60.5% depth. This falls squarely into the AGS ideal and GIA excellent ranges. However when I got someone to help me to run it through HCA the result was a 3.3..? Does this mean such stones should be avoided then?

But somehow with the 35.9/40.4 stone above which isn’t GIA excellent, a 0.8 HCA score was received?

Sorry for the very many questions, just a confused person trying to find my way!
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,855
GIA does not like shallow pavilion.
HCA does not like steep and deep stones in general.
AGS proportion cut table appears to be more balanced, but their ray tracing grading system can be unpredictable.

No one system is perfect.

What many recommend is a stone that scores well in all three systems.
 

candyfloss

Rough_Rock
Joined
Apr 20, 2021
Messages
52
This makes more sense now thank you!

I have done some more digging and found a couple of other stones, I do truly apologise but could you guys help me to see if any of these would have potential? Or are they all duds? Have included possible concerns in brackets. Thank you so much!!!

Stone #1
0.70ct, D, VVS2
Table: 55.5%
Depth: 62.8%
Crown: 35.7 deg (16%) [found another with 35.6 deg too]
Pavilion: 40.6 deg (42.5%)
Dimensions: 5.63 - 5.65 x 3.54 mm

Stone #2
0.71ct, D, VVS2
Table: 57.5%
Depth: 62.4%
Crown: 35.8 deg (15%)
Pavilion: 40.9 deg (43.5%)
Dimensions: 5.68 - 5.70 x 3.55 mm

Stone #3 (table > depth)
0.76ct, D, VS1
Table: 60.5%
Depth: 59.6%
Crown: 33.7 deg (13%)
Pavilion: 40.9 deg (43%)
Dimensions: 5.92 - 5.96 x 3.53 mm

Stone #4 (girdle is slightly thick)
0.78ct, D, VS2
Table: 55.5%
Depth: 62.5%
Crown: 35.1 deg (15.5%)
Pavilion: 40.5 deg (42.5%)
Dimensions: 5.83 - 5.87 x 3.66 mm
 
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