Pricescope recommended proportions & the Inverse Crown and Pavilion Relationship

[Garry H (Cut Nut)]

We have an informal group-think proportion recommendation often quoted to advise newbies on what to look for. I would like to discuss and consider widening that cut range in this thread.

• Most people have a budget, it might be $2,000 or $200,000. Often you do not know until they ask about a specific diamond. But for everyone who posts a question there might be dozens of live readers or lurkers and 100’s or 1,000’s who find a discussion and are influenced by it..
• We advise on color and clarity too, for example many people start out higher in clarity and we often bring them back to VS/SI1. Often F, G, H are safe cost effective color recommendations. Widening their cut criteria can help them heaps.
• The cut ranges we recommend tend to be tight and INHO will pass over many ‘good enough’ diamonds. Remember you all may be helping a newbie but don’t forget the lurkers who may have other agendas - must be one carat for <$4k etc and they might be too embarrassed to post.

I have been the ‘CutNut’ since the mid 1990’s when I knocked on Martin Rapaport’s door of his NYC office. I introduced myself as a diamond cut nerd; he flicked me a few diamonds and asked me to loupe them and tell him table size, crown and pavilion angles etc. After 3 or 4 stones he gave me my handle. In 1999 at his annual talk in Vegas he told the retail trade “if you aren’t adding value to the diamonds you sell you might as well be flippin hamburgers”. He showed a slide of Pricescope and said most retailers will disappear. I contacted the PS founder, Leonid, and offered to write a tutorial for the site. Rest is history.

My PS involvement has been based on helping people get better looking more beautiful diamonds buy learning and making life difficult for the dinosaur wholesale and cutter trade, who mostly still today flip diamonds. Today I get some criticism from elitist consumers and vendors who believe that everyone should buy the very best cut. And I agree, but realistically there are so many variables and unknowable’s that the average Jo/sephine is totally overwhelmed; most want a good enough or better diamond. My strongly held belief is that if I can help people get a better bigger looking diamond for their $$’s then a fair % will ‘get it’ – that is they will understand what we bang on about.

If their diamond gets more accolades than other peoples then there is a chance that we will convert some of them into addicts who will become one of you. And so many of you have become Supa Dupa Ideal Cut junkies. And that is fantastic because you really ‘get it’. Cut is King or Queen.

So the purpose of this discussion is to see if we can not widen the scope of our cut recommendations.

Maybe it can have a Good, Better and Best range? Supa Dupa being the very bestest.

 

[Karl_K]

So the purpose of this discussion is to see if we can not widen the scope of our cut recommendations.

Short answer: no
Long answer: a tweak here and there at the most.
Longer answer: none super ideals with good angles and imaging are already being approved of many times even if they are not super-ideal.

But specifically talking about angle relationships its a no.
The angles/%s have to work together that is fundamental and non-negotiable to me.

 

[diamondseeker2006]

I think the whole point is that we are helping people buy diamonds mostly unseen, and often we only have the light return images on the superideal cuts. As Karl already said, we've been recommending non-superideal stones from the big websites for ages. I recommend some stones that I personally would not buy to fit their budgets. However, I do recommend stones that are likely to have great light performance. It's impossible to draw a line around a wider range of stones when we have zero idea of what sacrifices would be made in buying that particular diamond.

I am curious about where you'd draw the next lines outside of what we normally recommend, Garry. But I don't think I can do it, in good conscience.

 

[oldminer]

We were on the same wavelengths years ago. The Ideal-Scope and ASET Scope allows appreciation of fair-better- best light return, but much of the advice folks get here is targeted to a somewhat narrow range of top end, best cut quality. The tools are really practical for wider application of grading. This leaves a lot of consumers who wish to make some reasonable compromise on cut out in a relatively empty zone where nearly no one is prepared to help them choose wisely. There are many "good enough" choices to be found which suit the purpose. While we know that's the case, if often appears that it is an unsupported function. However, such choices deserve to have available information and support.

Although the system I made back in the 80's and 90's is no longer out in general circulation, I came from an area where diamond cut quality was not at all appreciated or fairly evaluated for consumers. I saw the system as revealing truths about cut quality that were otherwise being concealed. My system only gave fair-better-best levels in a way that was possible back then, but it was useful screening advice which helped thousands of consumers to make valid, sensible and reasonably well informed choices on rounds and most fancy shaped diamonds in the normal colorless to lightly tinted ranges.

Expanding the already existing graphical images of best versus, average versus badly cut rounds and princess cuts to cover many other shapes would be a major achievement. If there were working samples of I-S and ASET for rounds and popular fancy shapes in five or six categories of light return/cut quality level a lot of consumers would be getting the sort of broad information necessary for a far wider audience.

I think of the many consumers I have met in credit type stores and major chain stores over these past years who hardly ever see a well cut diamond, but who trust the seller to give them a proper choice. The number of people and their buying power is huge, but most of them miss the information here and what we generally see promoted does not even apply to what they are often being shown. Of course, in all fairness, there are exceptions. It is not a simple story. Stores stock and sell what they are able to obtain and they have price points, sales volume targets, and horrific overhead issues which we can't really appreciate. But, Pricescope could be far bigger with easy to access, broader information and more complete visual tools for diamond grading.

If those tools were available, the pro-sumers and experts here would easily be able to refer folks to visually appreciate why very well cut diamonds are our favorites, but just like buying GHI color instead of EF, the consumer can make their own reasonable choice with their personal budget and expectations in mind. Having this would also make use of the I-S and ASET far easier to understand and bring many more users into the market. I'd love to see more retailers and dealers start using such simple tools for selection of their inventory. They won't do it until consumer demand forces them to change.

 

[the_mother_thing]

So the purpose of this discussion is to see if we can not widen the scope of our cut recommendations.

Maybe it can have a Good, Better and Best range? Supa Dupa being the very bestest.

Why can the HCA tool not be used to help buyers seeking non-super-ideals? 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 be ‘rejected’ 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:


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. (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 ). 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.

 

[Texas Leaguer]

The decision about what constitutes ‘good enough’ is an individual one based upon a consumer’s own particular circumstances and priorities. And that assessment cannot be made without knowing what the very best is.

Forum visitors come here for the purpose of learning about that range. It should NOT be the purpose of prosumers here to determine what is “good enough” for the OP and to promote that thing.

If the consumer market for diamonds (or any other product) was driven by “good enough” there would be no innovation. Marcel Tolkowsky would have chosen a different topic to write his famous thesis. Wade and Morse would not have made the economic sacrifices they did in order to cut for beauty over carat weight. The AGS would never have opened a lab focusing on cut quality and would never have invested in a completely new way of assessing light performance, along with other researchers like Octonus. Garry Holloway and David Atlas would not have done the hard work to create their tools. GIA would never have been forced by the market to release an overall cut grade.

This forum developed around the quest for knowledge about what constitutes the very best. Not what constitutes ‘good enough’. We are the tip of the spear, the cutting edge of the information age as it pertains to the diamond industry. Why should we now seek to blunt that edge? And will the consumer market be better off if we do?

Consumers and forum members alike realize that all but the billionaires among us must make some compromise when it comes to buying a diamond. But presenting the very best is the only way to make sure that a consumer does not make a decision about what is good enough for THEM without understanding the full range of possibility.

 

[Garry H (Cut Nut)]

Consumers and forum members alike realize that all but the billionaires among us must make some compromise when it comes to buying a diamond. But presenting the very best is the only way to make sure that a consumer does not make a decision about what is good enough for THEM without understanding the full range of possibility.

Thanks Bryan, and I surely do not want to misinform about what the best is, but this range can have some refinement. For example I would not want a 59% table on +2ct diamond. But I think (just as a 36 degree crown needs a shallower pavilion) a 'Good' range could include at least a 33 degree crown angle when combined with slightly deeper pavilion. Here is what is usually posted:

PS-recommended proportions are as follows:
Table 54-59%
Depth 60-62.4%
Crown Angle 34-35 degrees (up to 35.5 or maybe even 36 degrees with shall (40.6 degree) pavilion, but additional checks are needed)
Pavilion 40.6-40.9 degrees
And OhShiny wrote:
When crown angle increases, pavilion angle should decrease, as Garry has mentioned - so 35 crown with 40.6 pavilion, but 34 crown with 40.9 pavilion, etc.

 

[Garry H (Cut Nut)]

Inverse Relationship: These 2 videos made with DiamCalc will show what I mean by the 5:1 Crown : Pavilion angle relationship and that you can achieve great beauty (and often save money) across a range of proportions that is greater than the PS 'rules'.
Now these will not all be supa dupa sweetest spot diamond, but for the non elitiests on budgets - if they start with this and buy a diamond in the top 95% for beauty, then many will learn by comparison with friends and family diamonds that CUT is KING (or Queen).
One set of proportions are a little shallower - and in my experience work for all but the short sighted. The proportions show up in the top left of the videos

 

[Karl_K]

PS-recommended proportions are as follows:
Table 54-59%
Depth 60-62.4%
Crown Angle 34-35 degrees (up to 35.5 or maybe even 36 degrees with shall (40.6 degree) pavilion, but additional checks are needed)
Pavilion 40.6-40.9 degrees
And OhShiny wrote:
When crown angle increases, pavilion angle should decrease, as Garry has mentioned - so 35 crown with 40.6 pavilion, but 34 crown with 40.9 pavilion, etc.

My tweak is to add 41p with 34-34.5 crowns and 55-56 tables which is one of my favorite ranges when well cut,
60-60s
40.7-41p with crown angles around 33-34

 

[Garry H (Cut Nut)]

For example, I have a diamond that scores >2 on the HCA:


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. (That’s the message seemingly being communicated, at least).

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 ).

Just some random thoughts from a PSer who appreciates all diamonds from super-ideal to super-wonky.

Hi Mother Thing, Great post. If we use good better best how do we quantify 'Good'?

 

[Karl_K]

Inverse Relationship: These 2 videos made with DiamCalc will show what I mean by the 5:1 Crown : Pavilion angle relationship and that you can achieve great beauty (and often save money) across a range of proportions that is greater than the PS 'rules'.

For a pendants and earrings you can expand the range to the shallower pavilions.
At the steeper range you quickly run into color entrapment and under table leakage.
IS images does not tell the entire story.

edit: bad wording corrected.

If shopping for earrings for my sister I would start the hunt for a set of gia vg stones with a shalllow pavilion that is otherwise well cut and save a ton of money.

 

[OoohShiny]

EDIT: I am slow at typing and Garry has already referenced the other thread lol



I am wondering if this thread has been partly prompted by Garry picking me up on the 'PS-recommended parameters' in another thread and then the discussions that continued over the page:

Thoughts on this F with med blue fluorescence?

https://www.bluenile.com/ca/diamond-details/LD13344528 Thoughts and opinions on an F with med blue fluorescence, as well as the overall cut of this diamond? Thanks!!

www.pricescope.com

The videos of the different crown/pavilion combos, as well as the table posted from Octonus, are good demonstrations (that sort of make my head hurt ) of what different combinations can look like (in IS/ASET, and with the 'diffraction patterns' in Octonus as well), but as is discussed, even the experts disagree somewhat re: what makes a good-looking stone lol.

As mentioned by oldminer, I think it would be useful if we had a resource page with the large (AGS?) tables of ASET results for both MRBs (e.g. all the table sizes / LGFs / crown angles / pavilion angles) and also fancy shapes, so we could all have a central resource of them, along with a good explanation of the different colours and what they mean. I know the large tables are on here somewhere but I'm damned if I can find them when I need them lol

That could show visually to newbies (and more experienced members!) the difference in performance each change a parameter makes, as well as help identify borderline stones that might need more careful inspection (such as mentioned by Karl: https://www.pricescope.com/communit...hat-do-you-think-of-this.254172/#post-4666611) - but might it reduce use of the HCA tool??


One other thing, though - we talk about ASET and IS images in their face-on position only, but I have found the tilt-ASET images posted by Yoram previously (in Jimianne's 'Mildred' asscher thread) to be very interesting and useful in terms of understanding how light leakage can be incorporated into a cut in a not-negative way, as well as how a stone performs in motion. Might tilt-ASET also help increase the range of stones considered to have 'good potential', seeing as (as mentioned above) Serg prefers steeper/deeper combos that cancel out light leakage under the table to some extent with binocular vision and tilt angles?


(Does that make any sense??!)

 

[OoohShiny]

My tweak is to add 41p with 34-34.5 crowns and 55-56 tables which is one of my favorite ranges when well cut,
60-60s
40.7-41p with crown angles around 33-34

I think we definitely need more on 60/60s - generally and also with reference to / information on the super-duper 60/60s that I've seen said were cut historically!

 

[daisygrl]

I am a 34.5/40.8 type of a gal. My question is: would you reject a diamond that is 35/40.8 with a good Ideal Scope and a strong light return? (given that all other measurements check out)

 

[OoohShiny]

I am a 34.5/40.8 type of a gal. My question is: would you reject a diamond that is 35/40.8 with a good Ideal Scope and a strong light return? (given that all other measurements check out)

That combo is on the stone that Karl mentioned is borderline in the other thread:

deciding-to-go-a-bit-bigger-what-do-you-think-of-this.254172

so I think it would need careful inspection on a case-by-case basis.

 

[daisygrl]

That combo is on the stone that Karl mentioned is borderline in the other thread:

deciding-to-go-a-bit-bigger-what-do-you-think-of-this.254172

so I think it would need careful inspection on a case-by-case basis.

That is understandable. I asked because I was just browsing WF and saw many either ACA or Premium Select with 35/40.8 ratio. Surprisingly, a lot of them were ACA.

 

[Garry H (Cut Nut)]

EDIT: I am slow at typing and Garry has already referenced the other thread lol

Yes OhShiny
Here is the Master Stone Set image and link
http://legacy.octonus.com/oct/mss/table.phtml There are a lot of things y can click too

 

[Serg]

EDIT: I am slow at typing and Garry has already referenced the other thread lol



I am wondering if this thread has been partly prompted by Garry picking me up on the 'PS-recommended parameters' in another thread and then the discussions that continued over the page:

Thoughts on this F with med blue fluorescence?

https://www.bluenile.com/ca/diamond-details/LD13344528 Thoughts and opinions on an F with med blue fluorescence, as well as the overall cut of this diamond? Thanks!!

www.pricescope.com

The videos of the different crown/pavilion combos, as well as the table posted from Octonus, are good demonstrations (that sort of make my head hurt ) of what different combinations can look like (in IS/ASET, and with the 'diffraction patterns' in Octonus as well), but as is discussed, even the experts disagree somewhat re: what makes a good-looking stone lol.

As mentioned by oldminer, I think it would be useful if we had a resource page with the large (AGS?) tables of ASET results for both MRBs (e.g. all the table sizes / LGFs / crown angles / pavilion angles) and also fancy shapes, so we could all have a central resource of them, along with a good explanation of the different colours and what they mean. I know the large tables are on here somewhere but I'm damned if I can find them when I need them lol

That could show visually to newbies (and more experienced members!) the difference in performance each change a parameter makes, as well as help identify borderline stones that might need more careful inspection (such as mentioned by Karl: https://www.pricescope.com/communit...hat-do-you-think-of-this.254172/#post-4666611) - but might it reduce use of the HCA tool??


One other thing, though - we talk about ASET and IS images in their face-on position only, but I have found the tilt-ASET images posted by Yoram previously (in Jimianne's 'Mildred' asscher thread) to be very interesting and useful in terms of understanding how light leakage can be incorporated into a cut in a not-negative way, as well as how a stone performs in motion. Might tilt-ASET also help increase the range of stones considered to have 'good potential', seeing as (as mentioned above) Serg prefers steeper/deeper combos that cancel out light leakage under the table to some extent with binocular vision and tilt angles?


(Does that make any sense??!)

@OoohShiny ,

Ray Path in Round Diamond – docs

How stereo defines round diamond performance

docs.cutwise.com

Sweet Line in Round Diamonds – docs

Consider two dimensional Ca-Pa variations of the round parameters

docs.cutwise.com

Above links could help make some sense . check below image in dynamic .

 

[the_mother_thing]

Hi Mother Thing, Great post. If we use good better best how do we quantify 'Good'?

Admittedly, I don’t know enough about the inner-workings of the HCA to know what exactly/specifically is ‘graduatingly bad’ about diamonds as they go from 2.1 to 2.5, 3, 3.5, 4, etc. Maybe ‘Better’ is 2-3, ‘Good is 3-4’, and anything .4 = poorly cut/less than 25% light return. But I think the question isn’t so much ‘how to define good’ as it is "is a 2.5, 3, or 3.5 really ‘bad/poor/trash’?" Rather than reinvent the wheel, maybe it’d be helpful - IF it’s true/factual - to re-establish the mindset & expectations about what those >2 scores may look like for the segment of buyers who don’t demand/require ‘ideal’ or ‘super ideal’.

As is, we’re basically telling folks ‘>2 sucks, don’t buy it‘ but not clearly/consistently showing them why (the educational benefit of PS). For some, an HCA 2.7 may sparkle great, meet their needs and budget, and leave them perfectly happy with their choice and/or they may not feel they can discern the differences between a 2.7 and a 1.6. Others who are more eagle-eyed, discerning, etc., may easily see the difference, want the ‘Supa dupa’, but either way, everyone will have the peace of mind knowing they bought the ‘best’ for them based on their priorities.

Going back to the other threads about helping consumers, and the multitude of opinions expressed on PS, it just seems there could/should be a basic standard that can be easily articulated with video tutorials that consumers can see examples. So, for the HCA, if a 2.7 result is returned on a candidate stone, might it be possible to have a video simulating how that result may perform next to a ‘Supa-dupa’ 1.2, and a poor performing 5.8, and point out the differences to help them see and decide for themselves?

As a consumer, I like the idea that ‘basic’ performance factors are consistently articulated vs potentially confusing consumers with 50 different PSer/prosumer viewpoints, experience levels, spreadsheets, etc. ... not to mention I am not a fan of the suggestions to ‘reward’ prosumers due to the potential conflicts that brings, etc. Of course, PSers can/may/should still comment on threads where people are seeking feedback, share their pics, experiences, etc. but it’d be better if everyone was working with the same basic set of facts, so to speak. And we left the ‘facts’ from which buyers make decisions to the actual pros with the actual, hands-on experience vs multiple interpretations/perspectives based on the priorities and preferences of others.

That probably comes across as if I am bashing PSers who provide feedback, and that is not my intent; rather, just digesting the feedback from that discussion into suggestions for this potential solution.

 

[Garry H (Cut Nut)]

Like this OhhhShiny?

 

[OoohShiny]

Like this OhhhShiny?

That's the sort of table I was thinking of, yes!

@OoohShiny ,

Ray Path in Round Diamond – docs

How stereo defines round diamond performance

docs.cutwise.com

Sweet Line in Round Diamonds – docs

Consider two dimensional Ca-Pa variations of the round parameters

docs.cutwise.com

Above links could help make some sense . check below image in dynamic .

Thank you, Serg!

I must go to bed because it is very late! but I will read those in the morning

 

[Karl_K]

Another thing when you start playing around the edges the gia gross rounding really throws a monkey wrench in things.
There are combos that with in the gia rounding it could be ags0 or ags4 using the ags system.
Without advanced imaging they have a lower confidence in recommending them.

I have recommended stones thaat score 2.7+ hca and cautioned about others based on imaging for the same reason.
I seem to recall recomending a stone in the hca 3.5 range where imaging beet the gia rounded data hca score.

 

[AV_]

@Texas Leaguer It is nearly 4 am here & nothing is good enough.

[two weeks to a deadline]

 

[Garry H (Cut Nut)]

@OoohShiny ,

Ray Path in Round Diamond – docs

How stereo defines round diamond performance

docs.cutwise.com

Sweet Line in Round Diamonds – docs

Consider two dimensional Ca-Pa variations of the round parameters

docs.cutwise.com

Above links could help make some sense . check below image in dynamic .

Sergey there is more than one facet doubling up at one time, and it happens on Tolkowsky proportions too.
I agree the nail head will almost always have bad table region and loads of peripheral leakage. But this extremely shallow example (HCA doesn't like it) does not totally die in stereo.
DiamCalc supports stereo modeling which I use for fancy shape diamond selection with Ideal-scope (and sometimes ASET). But Youtube turns stereo videos into 2 seperate images playing side by side - so I made a video with my phone and computer screen (and apologies for Andrey sype calling me midway).

 

[Mlh]

That combo is on the stone that Karl mentioned is borderline in the other thread:

deciding-to-go-a-bit-bigger-what-do-you-think-of-this.254172

so I think it would need careful inspection on a case-by-case basis.

Here are the specs How does this one look with more detail? I tried to run the hca again but gave me an error message

 

[Serg]

Sergey there is more than one facet doubling up at one time, and it happens on Tolkowsky proportions too.
I agree the nail head will almost always have bad table region and loads of peripheral leakage. But this extremely shallow example (HCA doesn't like it) does not totally die in stereo.

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.
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"

 

[Karl_K]

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.
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"

No matter what you do a mrb is going to be directional, trying to make it something that is contrary to the design is not a good trade off in my opinion.
If you want a diamond that draws light from a wide area then a step cut or high top pear is a better choice.

 

[prs]

Thanks Bryan, and I surely do not want to misinform about what the best is, but this range can have some refinement. For example I would not want a 59% table on +2ct diamond.

Garry, sorry to digress from the main subject of your thread, but your comment about table size has peaked my interest. I don't know where it came from, but I have in my cut notes the following statement:

Holloway rule: 61% max table under 0.75 ct, 60% under 1.0ct, 59% under 2.0ct, and 58% for all above 2.0ct.

Would you be so kind as to explain this "rule". Is it just personal preference, or is it something specific about the optics in larger stones?

 

[Garry H (Cut Nut)]

Garry, sorry to digress from the main subject of your thread, but your comment about table size has peaked my interest. I don't know where it came from, but I have in my cut notes the following statement:

Holloway rule: 61% max table under 0.75 ct, 60% under 1.0ct, 59% under 2.0ct, and 58% for all above 2.0ct.

Would you be so kind as to explain this "rule". Is it just personal preference, or is it something specific about the optics in larger stones?

Thanks PRS,
It is observational.
Larger diamonds create more fire as a benefit and a smaller table increases that ability.
Smaller diamonds by themselves create very little fire so the main benefit comes from brightness for smaller stones which is helped along by larger tables.
Also looking into a big diamond with a big table means you see way less virtual facets and they look boring.

 

[Rockdiamond]

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