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Pricescope recommended proportions & the Inverse Crown and Pavilion Relationship

Garry H (Cut Nut)

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Garry, the page https://docs.cutwise.com/blog/ray-path-in-round-diamond touches 2 very important issues for diamond optical performance
1) Stereo rivalry :
Red +Red combination does not mean best Brilliancy.
Sometimes Red+White creates better Brilliancy.
I do not disagree Sergey, I am not sure how the effect can be quantified other than via a large scale long period of actual human and sales data. Cutwise.com could do that if it were to become a commercial monster.
My point with the above video was that there are many continual dark zones for both eyes even in Tolkowsky proportions and identifying just the two left and right central ones is an oversimplification.

2) VF's angular speed ( for main facet it strongly depends from pavilion angle.Main facet with shallow angles have much less angular speed compare with facet for Pavilion angle 41.8( I am not saying that Cr34.5 P41.8 is good or bad diamond. I am telling about angular speed which has high correlation with diamond "Life"). The Shallow diamonds could have high Light return but it have weak " Life."
Deep diamonds could have less Light return, but much bigger and attractive "Liffe"
 
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prs

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Respectfully have a different perspective Garry...
I hate to keep on and on about "the 60/60's of my youth" but it's not just a fond memory. I've seen such stones more recently, rare as they are- and with the correct ca/pa/lgf, the "vintage" 60/60 puts on an unrivaled light show- in large- and even ridiculously large sizes....
But of course, boring is in the eye of the beholder:)
@Rockdiamond I would really like to know what you consider the correct ca/pa/lgf for a >2ct 60/60.
 

OoohShiny

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Respectfully have a different perspective Garry...
I hate to keep on and on about "the 60/60's of my youth" but it's not just a fond memory. I've seen such stones more recently, rare as they are- and with the correct ca/pa/lgf, the "vintage" 60/60 puts on an unrivaled light show- in large- and even ridiculously large sizes....
But of course, boring is in the eye of the beholder:)
@Rockdiamond I would really like to know what you consider the correct ca/pa/lgf for a >2ct 60/60.
I would also like to see PS have more info on what an 'ideal' 60/60 might look like - if there are 'good ones' still out there, can we start to collate information on their proportions? :)
 

sledge

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Holy data tables....


We need something similar here....except expand to include black & white versions of ASET, IS and H&A's. Include all table sizes and 75, 80 & 85 LGF. Better yet, be awesome if there was a web app that you could enter up to 5 stones to compare and enter the proportions and it would populate the images -- all easy to copy/paste back into forum discussions.

Like @OoohShiny love the moving ASET's shown on this page about 2/3 down.


One very lacking feature on this site is good resources for comparing 60/60 against Tolk. We may be able to generate computer images, etc using software but imagine how awesome it could be if we had a CONTROLLED environment where individual users could submit video & photo of their diamonds using proper background, camera specs, etc. This data could be cataloged by their proportions and also pulled up in a web app when you enter appropriate data.
 

Rockdiamond

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@Rockdiamond I would really like to know what you consider the correct ca/pa/lgf for a >2ct 60/60.
I consider myself super lucky in this regard.
I'm confident that I could have taken the test Rappaport gave Garry all those years ago and correctly guessed table size....but not CA/PA...simply because there was no reason to learn them, in my position as a diamond grader of that day.
It was easy to identify the best cut stones for me. If you think about it- if you're looking at a diamond, you shouldn't need to know the CA/PA to appreciate the cut.
If one of our clients wants an RBC, I know how to use my eyes to pick the correct candidate.
Plus, there are so many different aspects to consider.
We recently had a great client looking for a pair of 5ct tw RBC's
The person had a strict budget ( who doesn't?) so we were relegated to J/SI2.
How many eye clean, 2.50ct J/SI2's do you think there are on the market?( that aren't hopelessly overpriced)
Percentage-wise....what's the difference in appearance between a stone with slight leakage (HCA3.5 )in the table to one with a 1.0 HCA?
Put another way- would you choose a 1.0 HCA stone that had a visible crystal, to a3.5 HCA stone who's SI2 crystal was tucked away, where it was invisible?
So as a buyer- even if you're a consumer- considering many aspects is important.
HCA is incredibly valuable- I love the idea of honing the scores to make it more relevant to the entire process.
 

Mlh

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My struggle as a consumer is identifying stones in budget and with the hca and the gia report in line. Then having to ask for images and the sarin report to ensure the gia rounding looks good. How many times can we ask this of a vendor before we try their patience? I have learned so much but keep learning. I keep trying. But the problem is context. I have not seen enough stones to know what to accept or reject. The stones look good to me. Then I wonder what don't I realize. Here is my current contender. In person it looks nice. I look at the charts and it seems to fall within acceptable ranges. SCANOX.JPG
 

headlight

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Why can the HCA tool not be used to help buyers seeking non-super-ideals? :confused: It’s always perplexed me that it’s consistently cited to be a ‘rejection’ vs. ‘selection‘ tool; however, the information it provides for stones that should berejected’ would lead users to believe/conclude otherwise. In other words, if it’s truly a ‘rejection’ tool, why even tell folks it scored >2, 3.4 or 5.9, and provide any of the commentary those scores provide? I think perhaps there’s opportunity there to consider ...

For example, I have a diamond that scores >2 on the HCA:
66ED85D2-58F9-4E98-8E9D-D0812432F73F.jpeg

It ‘should’ be rejected by current/normal PS-mantra, and the HCA tells me that it earns ‘very good’ light return, fire, scintillation & spread ... that it probably sparkles & looks a good size for it’s weight, and that if it scores <2.5, it “can” be a nice diamond ...

Bummer, it scored 2.7, so according to PS it can’t be a nice diamond. :cry: (That’s the message seemingly being communicated, at least).

Here’s the not-nice diamond (center of three stone) compared to my ACA (soli) - quick videos just taken indoors:


Is it supa-dupa-ideally-perfectly-cut? No, but is it really ‘rejection-worthy’ the way PSers advise buyers to dismiss >2 or even >2.5s)? Nope! It is quite fiery, sparkly and bright in person, and I imagine the average consumer with a budget targeting the .70ct range would be thrilled to have this diamond on their finger (if they can get beyond it’s “school-bus-yellow-K-color”, of course :razz:). These videos don’t show really how fiery it is, but I wore it to a function one night several months back and had several ladies come up to me after the speakers finished, commenting how it was a dancing ball of fire that kept catching their eye from several tables away. But ... PSers would say “hard pass” because of the HCA score alone.

So is there maybe an opportunity to consider how the HCA tool is referenced/promoted/leveraged by people with budgets big & small, seeking super-ideal and not-so-super-ideal-but-still-super/pretty-sparkly diamonds. Can it be ‘retooled’ (or a similar/simpler tool created) leveraging the reasonably-predictable results of certain proportion specs and/or characteristics to provide a general yet realistic ‘performance expectation’ that can be level-set by a consistent set of criteria using the AGS/GIA report that aligns with your “Best/Better/Good” approach (with the caveat that clarity and other factors could impact the performance and should be confirmed by an independent appraiser/gemologist/etc.)?

It would likely take some reworking the verbiage a bit so that it doesn’t conflict with advise given in other areas ... for example, PSers frequently advise ‘newbies’ that “very good” on a GIA report really isn’t “very good”. Yet, the ‘very good’ on my HCA result above - IMO - actually is pretty darn good (seeing this diamond in person). So which is it? Is “very good” very good or is it not? Perhaps instead of using Excellent/Very Good/Good, you can use different terms or a scale so as not to create confusion between GIA terms?

Just some random thoughts from a PSer who appreciates all diamonds from super-ideal to super-wonky. :wavey:
These images are VERY compelling and it does give some credence to the framework of the GIA Cut Grading System where many different sets of proportions can yield an attractive stone.

I love your ideas and agree that the HCA seems to have immense potential to be adapted for applications well beyond what it is currently.

We know the AGS0 stones need no questioning. But it does seem that there are stones that do not have that credential that are still beautiful stones... we just need a way to make finding them easier!

I think that there are some elements of a super ideal that ultimately may not be seen beyond the images. Where real life viewing differences are so indiscernible between the 0s and this other group of stones that shouldn’t be disregarded. And for people who don’t feel the need for a super ideal, these stones can provide a great opportunity. It can afford someone a larger stone, or a higher color grade.

As an aside, I love your jewelry (but you already know that!).
 

Serg

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My point with the above video was that there are many continual dark zones for both eyes even in Tolkowsky proportions and identifying just the two left and right central ones is an oversimplification.
Garry,
did you check movies for left and right eyes in the end of page
?
There is either stereo contrast or dynamical contrast for each facet in Tolkowsky and Diamond P41.4 diamonds. Some of them have both type these contrasts in same time. When in the shallow diamonds we see all main facets as black by 2 eyes for all tilting positions.
it is huge difference without any simplification .
Screenshot 2020-01-22 04.48.31.png
 
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Karl_K

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@Serg
There is an inverse relationship between pavilion depth and the reaction to obstructing distance.
In other words a shallower pavilion will show more reaction to obstruction at a given distance then a deep pavilion.
So at lets say 12 inches a 40.4 pavilion will show the effects of obstruction on the mains more than a 41.4 pavilion.
I also agree that it will also show the effect of obstruction more with tilt.
However the difference is not linear there is a cliff at around 40.45 degrees where it increases quicker and there is another cliff at the other side that varies based on crown angle where it decreases quicker.
In the what is considered near tolk range of 40.6 to 40.9(41 some combos) the difference between them in the reaction to obstruction is less.
 

Mlh

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My struggle as a consumer is identifying stones in budget and with the hca and the gia report in line. Then having to ask for images and the sarin report to ensure the gia rounding looks good. How many times can we ask this of a vendor before we try their patience? I have learned so much but keep learning. I keep trying. But the problem is context. I have not seen enough stones to know what to accept or reject. The stones look good to me. Then I wonder what don't I realize. Here is my current contender. In person it looks nice. I look at the charts and it seems to fall within acceptable ranges. SCANOX.JPG
@Serg, @Garry H (Cut Nut) @Karl_K is this falling in good range or too deep? Or does in person matter more here?
 

Serg

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@Serg
There is an inverse relationship between pavilion depth and the reaction to obstructing distance.
In other words a shallower pavilion will show more reaction to obstruction at a given distance then a deep pavilion.
If a diamond does not look good on 350mm distance from observer it does not a good diamond.
we can not ask a consumer to see a diamond only from big distances

@Serg

In the what is considered near tolk range of 40.6 to 40.9(41 some combos) the difference between them in the reaction to obstruction is less.
why have we reject 41.2 for stereo observer ? 41.2 has less obscuration , it has better VF's speed, it has better Dispersion , it has better Stereo rivalry in compare with 40.6-40.9 range.

Who, When, How did proof P40.75Cr34.5 as best for a Stereo observer and a tilting diamond?
 
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Karl_K

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why have we reject 41.2 for stereo observer ? 41.2 has less obscuration , it has better VF's speed, it has better Dispersion , it has better Stereo rivalry in compare with 40.6-40.9 range.
It can also lacks contrast for contrast brilliance at close range and I do not like darkness between the mains with higher crowns and am not a fan at all of low angle flat tops.
 

Karl_K

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Who, When, How did proof P40.75Cr34.5 as best for a Stereo observer and a tilting diamond?
I don't make such a claim, I do not believe that any "1" combo is the best.
 

Serg

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Sergey how far along the sweet ling would you go in each direction?
Many PS people recomend up to 36 crown with 40.5 pavilion. I agree. What people have not been recommending is deeper pavilion shallower crowns. I like down to 41.3/32.
Garry,
Diamonds on Sweet line are not identical . Most probably most consumers and expert will not see a difference in performance for he Pavilion variation +/-0.2 degree( that is equal to 1 degree crown variation). I am not sure about +/-0.4 degree Pavilion variation.
it is much less important question than
1) comparison between sligthly shallow pavilion( P40.4) and slightly steep Pavilion( P41.2)
2) Comparison between P40.8 and P41.2
Before we agree in a results of such comparison, I do not see a reason to discuss a length of a sweetline.
Firstly we need find( define) a starting point for the sweetline
 
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Garry H (Cut Nut)

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Garry,
Before we agree in a results of such comparison, I do not see a reason to discuss a length of a sweetline.
Firstly we need find( define) a starting point for the sweetline
I would add Sergey that there are other factors to consider such as:
1. ring vs pendant
2. diamond size (smaller diamonds usually do not face direct to wearer)
3. keeping lower colored diamond looking whiter
4. Edited to add - possibly lower girdle facets ranges
etc
 
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Rockdiamond

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Guys- the most recent charts you've posted * such as the one in post #45)- are they all the same LGF%?
 

sledge

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Guys- the most recent charts you've posted * such as the one in post #45)- are they all the same LGF%?
Yes. All 57 table, 80 LGF & 50 stars. Only variation is CA & PA.

Clarified in the first paragraph on this page, which is where these graphics are taken.

 

Serg

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I would add Sergey that there are other factors to consider such as:
1. ring vs pendant
2. diamond size (smaller diamonds usually do not face direct to wearer)
3. keeping lower colored diamond looking whiter
4. Edited to add - possibly lower girdle facets ranges
etc
Garry, it is possible to add 100+ more questions and conditions and discuss it without any results next 10 years again . Sorry, I am too boring . I prefer fancy cuts. See fancy cut variations and compare it with questions about round cut

 

prs

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I'm confident that I could have taken the test Rappaport gave Garry all those years ago and correctly guessed table size....but not CA/PA...simply because there was no reason to learn them, in my position as a diamond grader of that day.
It was easy to identify the best cut stones for me. If you think about it- if you're looking at a diamond, you shouldn't need to know the CA/PA to appreciate the cut.
Thanks for your reply @Rockdiamond I was trying to figure out what the angles might be on one of your fabulous 60/60 stones when I realized I didn't know what exactly a 60/60 diamond is. Is it a diamond that both table and depth are exactly 60.0%, or is it a diamond with both table and depth exceed 60.0%?

If you do come across another example of a fabulous 60/60, maybe you could be kind enough to share the GIA with us.
 
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Karl_K

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One very lacking feature on this site is good resources for comparing 60/60 against Tolk. We may be able to generate computer images, etc using software but imagine how awesome it could be if we had a CONTROLLED environment where individual users could submit video & photo of their diamonds using proper background, camera specs, etc. This data could be cataloged by their proportions and also pulled up in a web app when you enter appropriate data.
Generic computer generated images or an image of a similar stone are not representative of the stone in question.
They are great for general learning but not when applied directly to a specific diamond even using AGS numbers versus GIA garbage numbers.
 

Rockdiamond

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@prs - at this point, the “bloom is off the bush” when it comes to 60/60. For many reasons- yield is the main culprit. When I was a young pup a 1.00ct RBC was about 6.5mm. Nowadays the average is surely in the 6.3”s.
The beauty of the 60/60 wasn’t about heart and arrows or patterning. It was scintillation. That made them far easier to grade in terms of cut.
That’s why I never needed to learn to visually identify CA/PA.
In general- even the 60/60s of today rely more on patterning and don’t spread like the stones of the 80’s
Generally the only 60/60 stones I see which look like the olden ones of my (misspent) youth are actually antique stones still in the market.
 

Mlh

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My struggle as a consumer is identifying stones in budget and with the hca and the gia report in line. Then having to ask for images and the sarin report to ensure the gia rounding looks good. How many times can we ask this of a vendor before we try their patience? I have learned so much but keep learning. I keep trying. But the problem is context. I have not seen enough stones to know what to accept or reject. The stones look good to me. Then I wonder what don't I realize. Here is my current contender. In person it looks nice. I look at the charts and it seems to fall within acceptable ranges. SCANOX.JPG
I just got this stone today. Compared to my last stone which was 34 cr/40.6pav, it looks less dark to me. Is that the depth @Serg?
 

sledge

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I just got this stone today. Compared to my last stone which was 34 cr/40.6pav, it looks less dark to me. Is that the depth @Serg?
With a shallow 34 crown and shallow 40.6 pavilion I would anticipate you'd also have shallow depth.

My guess is these factors played together to create obstruction which made the stone look darker.
 

Serg

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Generic computer generated images or an image of a similar stone are not representative of the stone in question.
They are great for general learning but not when applied directly to a specific diamond even using AGS numbers versus GIA garbage numbers.
Screenshot 2020-01-27 08.18.51.png
 
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