Wriggle Room in Paul Gias Ideal Proportions ?

[donny17984]

Hey guys just wondering if there is any wriggle room from the ideal proportions that Paul Gias states in beyond 4c's
See below:

PERCENTAGE TO BE WITHIN 54.0% – 57.0%
DEPTH PERCENTAGE TO BE 61.0% – 62.5%.
PAVILION ANGLE IS WITHIN 40.6° – 41.0° RANGE.
CROWN ANGLE IS WITHIN 34.0° – 35.0° RANGE.

I really want to get a 1.5 carrat g to h colour, eye clean preferably Vs2 to Si1, excellent cut for around 14k AUD. when I do a more detailed search and punch in the ideal proportions there is nothing 1.5 carrat in the price range. Can any of those proportions be slightly out, if the hearts and arrows from the ideal scope images all check out!?

 

[ringo865]

Not sure of the exchange rate, but have you tried looking for, say 1.35 and up? And just outting SI1 and up (not limiting to SI1/VS2), maybe including I color? Something OTHER THAN CUT will have to be compromised for your budget.

 

[donny17984]

Ok mate no worries do you think the size difference will be very noticeable between 1.35 and 1.5?
How can I make the diamond stand out and look bigger? I was going for a halo setting but changed my mind now to a solitaire. If she wants a halo we can do one after. I really would like to avoid "I" colour as she is a bit fussy and would prob prefer as white as possibly. Happy to go to SI1 eye clean.

 

[donny17984]

Also if I was to go a halo in 1.35 carrat what are the best size diamonds to use on the outside. I don't want to take away from the centre diamond?

 

[tyty333]

For the depth we usually go 60-62.3. Just make sure if you go with 62+ that you are not losing too much diameter for the carat weight.

 

[SimoneDi]

Alright, I realize that this is going down in color, but the blue flouro helps the color significantly in my opinion. Ideal proportions http://www.briangavindiamonds.com/d...1.511-j-si1-round-diamond-ags-bl-104093735056
Alternatively, you can save some money by going just under the 1.5ct mark:
http://www.briangavindiamonds.com/d...1.444-j-si1-round-diamond-ags-bl-104093735057
Or if you go a bit lower in size:
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3838488.htm
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3586203.htm
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3738909.htm

I would not be opposed to I color in a super-idea in order to pick up a bit extra size. The difference between 1.3 and 1.5 is not terribly significant, but it is there. You just need to decide what is more important to you - size or color. Don't forget that there is always the option to upgrade, if desired, in the future.

 

[Rockdiamond]

Hi donny17984
Keep in mind that the extremely narrow portion set you've listed is just a preference within Excellent cut diamonds.
Many people will prefer proportions outside that list. Many other proportions that fall outside the list produce incredibly well cut diamonds.

 

[donny17984]

Hi donny17984
Keep in mind that the extremely narrow portion set you've listed is just a preference within Excellent cut diamonds.
Many people will prefer proportions outside that list. Many other proportions that fall outside the list produce incredibly well cut diamonds.

Hi There, From what I read there is absoulutely no wriggle room outside of the obove dimensons.
What proportions would you recommend that would be acceptable to get a Excellent cut diamond.
Without viewing the diamond with a trained eyes its hard to get it right and those proportions provide a good base to not getting something less desirable. Cheers

 

[Rockdiamond]

Hi donny,
Remember, this is the internet.
If I started a discussion of chocolate versus vanilla, we'd have a war in no time.
Folks that love the particular dimension set you list will argue to the death (figuratively) that a diamond has GOT to be within those #'s to be perfect. No question they are good numbers.
But there are many other proportions that some/many people prefer based on visual characteristics. GIA has an EX cut grade that includes the numbers you list- and many others. AGSL also has a Cut grade.
Both are respected. GIA's is far more widely respected- however AGSL is more respected here on PS
The point is, if someone is showing you a GIA graded EX cut grade diamond and it's outside the numbers you list, they are not necessarily trying to sell you something defective. I'd suggest looking at it ( if it's in person)
For me, and many others, 61% is just too deep for a beautiful modern Round Brilliant Cut.

 

[gm89uk]

Hi Donny, I have to say the above post really dilutes and dismisses why ideal proportions are more preferred here. Also AGSL cut grading is entirely different from GIA and you really not being told the full story by only stating GIA is far more respected. GIA simply has more global presence and is much wider than AGSL0. High proportions of GIA excellent cut are much deeper than 62 and this allows the industry to save carat and earn more.

I'm short for time but there are several educational videos comparing certain GIA excellent stones compared to AGS 0 (and other GIA excellent stones). Good old gold have a few of these on YouTube.

Nothing comes free in diamond proportions and a 60% depth while it gives you spread will often mean you have a larger table (usually but not always with a shallower crown) which leads to a smaller crown height percentage. This is where most of dispersion of a diamond is apparent and although brightness is excellent with this proportion, fire is compromised.

Rickdiamond has repeatedly expressed his preference for 60:60 stones with skinny arrows giving a more white splintery sparkly look while many consumers here prefer a more balanced firey look with chunkier arrows to get bolder flashes of light.

Garry H on the flip side has talked about how his experience that deeper stones with more fire are usually what is selected on blind tests for e rings and had similar resistance to Rickdiamond about this.

For me, buying off the internet, with significant cost savings / convenience / international consumers / these sets of proportions that offer the most balanced diamond, which offer safe options.

A friend of mine recently bought a shallow GIA XXX and it really is a dull stone in comparison to typical toll proportions. I feel that although they can be cut well, the more you get towards the deeper or shallower end of GIA X, cut precision is decreased (as tolk proportions are simply more popular)

 

[Rockdiamond]

Just for the record gm89uk Garry and I are pretty much on the same page now regarding this issue.
My user name is Rockdiamond btw. But you can call me Rick.
So many aspects of your post are simply incorrect gm89uk. I mean, if you're interested in learning.
You can surely speak for yourself and your taste but there's no reliable gemologist or expert that would call the type of diamond you like as " more balanced" than 60/60.
I could easily make the case that a well cut 60/60 is far more "balanced" than a tolk in terms of light performance.
There surely are some GIA EX cut grade stones above 62% however they are not all that common.
Your "feelings" about 60% depth stones being cut to a lesser degree of precision has no basis in reality.
Also- the anecdotal "my friend bought one and it was horrible" are not useful. We don't know anything about the stone your friend bought. How shallow is it?
You've also dragged out the old "greedy cutter" scenario.
What makes you think cutting to tolk gives a lower yield than 60/60? Far more likely that that tolk stone is better at saving weight for the cutter.

 

[gm89uk]

Just for the record gm89uk Garry and I are pretty much on the same page now regarding this issue.

Actually I never commented regarding whether you and Garry were in agreement. I simply stated that he also had resistance I read on the forum for encouraging FICs proportions against the army of prosumers that were strict in their preference for TICs. I likened it to the similar fashion of what you are going through with 60:60 stones now.

My user name is Rockdiamond btw. But you can call me Rick.
As mentioned in my post I was rushed, and was typing from my phone, so you'll have to excuse the typos (somehow autocorrect prefers rickdiamond), I have removed that suggestion

So many aspects of your post are simply incorrect gm89uk. I mean, if you're interested in learning.
You can surely speak for yourself and your taste but there's no reliable gemologist or expert that would call the type of diamond you like as " more balanced" than 60/60. I could easily make the case that a well cut 60/60 is far more "balanced" than a tolk in terms of light performance.

I'll clarify on my admittedly vague terminology. The optical properties are different for 60:60 and more traditionally recommended values. 60:60 stones (and by no means the rule) are more likely to have shallower crowns and crown heights. FICs are the other way and TICs are in the middle. Dispersion between these categories will look different, fire is usually less in these diamonds than FICs, TICs generally are a more balanced set of proportions between fire and brightness as qualities. I am NOT saying dispersion is lacking in a 60:60 but it is different than in an FIC, and fire is a quality that is relatively reduced. There are many discussions on this involving yourself.

" no one diamond can not have Highest Brightness and Highest Fire in same time" . If You optimize cut for Fire you lose some brightness and via versa if you optimize cut for brightness then you lose some Fire" Serg.

This is what I'm trying to say and I am NOT putting this as an umbrella above all 60:60 rather as a general trend. You can have afterall have stones like this: https://enchanteddiamonds.com/v/3837Z1595 (59/59/35/40..

The above stated proportions seem to be a middle ground.

If what I am saying is factually incorrect about basic optical properties of a diamond, please correct me, with a valid explanation.


There surely are some GIA EX cut grade stones above 62% however they are not all that common.

Where is your evidence?

Are you stating that shallower GIA stones are more common? Really? I don't have access to rapnet as you do, I will look at JA virtual inventory. Looking on GIA X cut on across carats 0.05ct to 30ct, there are 57,126 diamonds. If I limit depth to >=62.1% I get a return of 29,552 diamonds. 51.7% is not what I would call "not all that common". If I limit carat size to >0.7 then that proportion rises to 54.3 and to 55.1% at 1.5 carat plus. If JA virtual inventory if 57,126 is not reflective of the market then ignore this information.

Your "feelings" about 60% depth stones being cut to a lesser degree of precision has no basis in reality.

I am allowed to have opinions on my experience, I have seen less optical symmetry in shallower stones than I have in tolk proportions. If this is something against most vendors experience then I stand corrected.

Also- the anecdotal "my friend bought one and it was horrible" are not useful. We don't know anything about the stone your friend bought. How shallow is it?
You've also dragged out the old "greedy cutter" scenario.

Of course this is a single case scenario, and not evidence by any means. I can and will reflect on these experiences. I understand it's not the best angles for a 60/60 cut. Reasonable brightness (not excellent), but fire to my eyes is where it is really lacking. It's a 61T/59.5D 32.5/41.4 and 3% girdle. Arrows are skinny, appears messy, table reflection is large and HCA 3.7. Not even on the border of GIA X in terms of CA/PA.

What makes you think cutting to tolk gives a lower yield than 60/60? Far more likely that that tolk stone is better at saving weight for the cutter.

I'm not sure where I ever stated cutting tolk gives lower yield than 60/60. I said many GIA EX are deeply cut stones for weight retention.

Incidentally there is some information here regarding yield and 60 60 stones. https://www.whiteflash.com/about-diamonds/diamond-education/60-60-diamonds-1503.htm
Ultimately comments such as GIA cut grading is more respected than AGSL without any explanation to the pros and cons of both are in my opinion quite misleading comments to a lab (AGSL) that is already far less established. This is a subjective comment and has extra weight coming from a vendor as yourself. There are many people here that respect AGSL more than GIA EX.

I will have to respectively question the unbiased accuracy of some of your responses, particularly on answering on statements I did not make. I'd like to think I clarified when something is 'a hunch or feeling' and something that is a bit more concrete as to not misadvise.

 

[totallyfree]

Hey OP, great to see another Aussie! I too struggled with my diamond purchase, which was mostly about the currency exchange and not wanting to over estimate how far my $ would go. I am not an expert on the 'ideal' proportions but my argument is that there is absolutely 'wiggle room' as your preferences for a pretty/shiny/sparkly diamond will be different from mine. There is no one size fits all, perfect diamond indicator.

Would you consider a non-trade purchase (ie, preloved)?

 

[Rockdiamond]

Peace gm89uk- first and formost, I apologize if my response earlier was harsh.
It's a battle which was going on for so long, I'm surely a bit over sensitized.
Also- I stand corrected regarding GIA and just how common stones with greater than 62% depths.
62-63% yields the highest results.
This is a shock to me- I have not searched for rounds on rapnet for a number of years.
When we need round diamonds, they're always from people I know, and cut well.
In my search today, I actually found a GIA XXX 1.00ct that spread 5.89mm ....wow
I will reconsider my statements about GIA EX cut grade.
Regarding the rest of the points we're discussing, I do have some ideas, but I'll think a bit more before responding this time

 

[Rockdiamond]

Getting back to the discussion- which I very much appreciate:
The main core of the discussion is why I feel it's important not to eliminate 60/60 from one's searches for super well cut round diamonds.
Part of the premise of prior discussions somehow linked my defense of 60/60 as siding with greedy diamond cutters making a fortune by selling badly cut diamonds. I again apologize in this regard, because we do in fact, agree. Many diamonds are way too deep. The extra depth helps cutters to maximize weight- and they're really going overboard. I wasn't aware before today how prevalent it's become.
But back to our main discussion- I just did a bit of research.
Using widest possible parameters on Rapnet
no color, or clarity selected. Size .10ct-30cts
Round brilliant XXX GIA
Table 57-57.5
Depth 61.5-62
about 24,000 results.
Change to
Table 59.5-60
Depth 59-60
A bit less than 10,000 results.
60/60s are realtively rare.

Add one parameter- the weight of exactly one carat. On the smaller tables, we get an average of about 6.4mm. The largest stone is 6.48 the smallest is 6.34
The 60% group, the average is about 6.5mm. Largest stone 6.57mm smallest 6.44

We can discuss the different balance of fire scintillation and contrast we prefer- but there's no argument that some people will love the extra size when comparing two diamonds.
About your concerns around cut quality on the 60/60 stones. Considering their rarity, I could easily make the case the by going for 60/60 you're more likely to get a stone where the cutter cared, more than the 62% depth cutters, unless we're comparing to super ideal cuts.
Given that I don't look at nearly as many rounds as fancy shapes, and my experience today, thanks again to you, of a new outlook on the broader market- take this for what you may....but when I've seen 60/60's over the past few years, they were well cut.

About that balance of light performance properties- I believe there's too much weight placed on fire, and not enough on scintillation in discussions here. The super ideals strive for max fire and contrast.
About AGS- because it relates to this discussion- they're an outstanding organization. I could not respect them more.
GIA is just far more widely known, therefore more widely respected.
You're 100% correct, both have their merits.
I feel AGSL also places too much emphasis on contrast and fire.
GIA ( obviously) allows too many bad combos.
But it also places a higher degree of importance in scintillation, less on fire, optical symmetry in the cut grade. Which allows not only those deep monsters, but some really cool, nicely spreading high scintillating 60/60's. Of course, AGSL will 000 a 60/60 as well- but that's not what people are going for if that's where they are submitting likely.
And that's at the heart of the discussion too.
GIA includes diamonds that are more "sparkly"- because they lack the patterning of H&A.
My preference personally is to place a higher importance in scintillation and spread.
In the "real world" showing actual people diamonds, I've found many share my preference.

 

[Garry H (Cut Nut)]

Hey guys just wondering if there is any wriggle room from the ideal proportions that Paul Gias states in beyond 4c's
See below:

PERCENTAGE TO BE WITHIN 54.0% – 57.0%
DEPTH PERCENTAGE TO BE 61.0% – 62.5%.
PAVILION ANGLE IS WITHIN 40.6° – 41.0° RANGE.
CROWN ANGLE IS WITHIN 34.0° – 35.0° RANGE.

I really want to get a 1.5 carrat g to h colour, eye clean preferably Vs2 to Si1, excellent cut for around 14k AUD. when I do a more detailed search and punch in the ideal proportions there is nothing 1.5 carrat in the price range. Can any of those proportions be slightly out, if the hearts and arrows from the ideal scope images all check out!?

I rather wish Paul Gian would fix his glaring mistakes.
http://beyond4cs.com/2012/09/is-the-hca-score-always-reliable/
He knows about it since August 25, 2016
"Hey Gary,
Thanks for dropping by and leaving your comment. I’ve checked the url listing again. Gosh, I did make a mistake there and slipped up by assuming the images were correct without doing a proper verification against the proportions. I’ve updated the post.
Paul
- he has even had a reminder last month - and still has done nothing. So maybe it is an affiliate strategy to gain traffic?

 

[bmfang]

Paul Gian's website was one of the first that I came across when I began studying diamonds as a hobby. And then I realised that if I really wanted super-ideal stones, it was just easier to look at a number of grading reports of BGD and WF ACA stones to work out what their specs were for use if I was going to search JA or BN. I'd take his preferred specs as just that: his preference. You can find plenty of affiliate sites with this type of info on there which will all reveal their inherent preferences.

 

[gm89uk]

Getting back to the discussion- which I very much appreciate:
The main core of the discussion is why I feel it's important not to eliminate 60/60 from one's searches for super well cut round diamonds.
Part of the premise of prior discussions somehow linked my defense of 60/60 as siding with greedy diamond cutters making a fortune by selling badly cut diamonds. I again apologize in this regard, because we do in fact, agree. Many diamonds are way too deep. The extra depth helps cutters to maximize weight- and they're really going overboard. I wasn't aware before today how prevalent it's become.
But back to our main discussion- I just did a bit of research.
Using widest possible parameters on Rapnet
no color, or clarity selected. Size .10ct-30cts
Round brilliant XXX GIA
Table 57-57.5
Depth 61.5-62
about 24,000 results.
Change to
Table 59.5-60
Depth 59-60
A bit less than 10,000 results.
60/60s are realtively rare.

Add one parameter- the weight of exactly one carat. On the smaller tables, we get an average of about 6.4mm. The largest stone is 6.48 the smallest is 6.34
The 60% group, the average is about 6.5mm. Largest stone 6.57mm smallest 6.44

We can discuss the different balance of fire scintillation and contrast we prefer- but there's no argument that some people will love the extra size when comparing two diamonds.
About your concerns around cut quality on the 60/60 stones. Considering their rarity, I could easily make the case the by going for 60/60 you're more likely to get a stone where the cutter cared, more than the 62% depth cutters, unless we're comparing to super ideal cuts.
Given that I don't look at nearly as many rounds as fancy shapes, and my experience today, thanks again to you, of a new outlook on the broader market- take this for what you may....but when I've seen 60/60's over the past few years, they were well cut.

About that balance of light performance properties- I believe there's too much weight placed on fire, and not enough on scintillation in discussions here. The super ideals strive for max fire and contrast.
About AGS- because it relates to this discussion- they're an outstanding organization. I could not respect them more.
GIA is just far more widely known, therefore more widely respected.
You're 100% correct, both have their merits.
I feel AGSL also places too much emphasis on contrast and fire.
GIA ( obviously) allows too many bad combos.
But it also places a higher degree of importance in scintillation, less on fire, optical symmetry in the cut grade. Which allows not only those deep monsters, but some really cool, nicely spreading high scintillating 60/60's. Of course, AGSL will 000 a 60/60 as well- but that's not what people are going for if that's where they are submitting likely.
And that's at the heart of the discussion too.
GIA includes diamonds that are more "sparkly"- because they lack the patterning of H&A.
My preference personally is to place a higher importance in scintillation and spread.
In the "real world" showing actual people diamonds, I've found many share my preference.

Thanks Rockdiamond for your response. Interesting statistics! What would be interesting but not easy to do with a quick search is if there is a variance in price per carat for these 1carat stones. Does rapnet allow you to search by diameter or did you just have to look through individually?

As you say AGSL have predefined set of variables as you say which is up for debate as to whether they actually contribute to more beautiful stones in a majority of people. I think it's main merit is that it cannot be abused by cutting to the edge of the tolerability of what is acceptable (or to a much lesser degree). However whether it unfairly knocks perfectly beautiful stones to AGS1s and 2s for things that a majority people wouldn't care (or even prefer) next to an AGS 0 I am yet to see any studies or references regarding this.

Saying all this looking at the proportion tables as you say https://www.americangemsociety.org/Content/uploads/85481435071929.pdf AGSL0 allows for a large range of proportions at 59% an 60% that allow for 60% depths with reasonable girdle thickness.

So is AGSL really the problem or just that it has become associated with a must for superideal cuts and as such a skew in what stones are cut aiming for AGS 000. I'm sure GIA didn't set out to lay a variety of proportions that could be used to maximise rough as is being used today but unfortunately that is what has happened.

I'd be interested in hearing from yourself regarding the nice collection of 60:60 stones that you have seen (GIA graded) whether any would not have been eligible for AGS 0 based on those proportions table.

Looking again at JA, 0.05 to 30ct, wide as possible there are 699 AGS 0 & 1s (cannot separate excellent from ideal cut on JA)..
-Limiting table to 59+ and depth from 59 to 61, there are 39 hits (5.1%)
-Limiting table to 54-57, depth from 61 - 62 there are 370 hits (52.9%) hits. There are AGS 000 ideal right up to 62.8

What I mean is many proportions that AGS000 allows (and HCA), people here would not recommend. So really is there a problem with AGS000 being too restrictive, or the ideal proportion culture here on pricescope and on popular tutorials and blogs?

 

[Rockdiamond]

I love this discussion- thank you sincerely gm89uk
The issue that initially occurred to - many years ago here on PS - was that new technology was being used to document the way light moves through a diamond.
This was probably around 2003. A few years before GIA unveiled their cut grade.
Remember I was trained to grade diamonds at Harry Winston 1976-1979.
The House of Winston cut to 60/60. No one even looked at GIA reports back then. Nor were there Sarin machines. I don't k ow the specific CA/PA but I do know the LGF was around 80. No H&A. Less contrast more scintillation and spread.
Mr Winston loved the open look of a 60/60.
That's what was cut on 56th Street.
Back then a company called Lazar Kaplan specialized in "Ideal Cut" diamonds. They were gorgeous. The table (56%+-) looked tiny to me. But I could see the beauty in them. They also did not spread like the Winston 60/60

Fast Foward to my first PS membership. Before the old owners banned me.
Companies ( some still around) were promoting stones modeled after the LK Ideal cut and using reflectors to justify trashing stones like the ones I was reared on.
I just have to put this out there- people pay a premium for cut- there's a lot of money at stake for people selling Ideal cuts. Not for me- we don't carry all that many "traditional" RBC's.
But I still care about them- and the industry relations with the end user.
So my disposition was unique- and it still is among the trade. I'm pretty much the lone voice on this side- although the situation has gotten far less nasty.
I cut my teeth with old timers back then- long gone.
The newer thinking took hold on the web especially.
Fast Foward to today and I can see that I was fighting for a loosing cause.
Cutters LOVE deeper stones. Even AGSL graded stones. Not all of course but I guarantee you cutters can save more weight going for the small table 62 depth even in top rated stones compated to going for the type of stones Winston used to cut.
The spread tells that story in an objective manner. There's no opinion involved in how many mm a diamond spreads for the weight.
Yes I can search by diameter when I get back to work tomorrow.
Sorry for the long answer.

 

[Texas Leaguer]

GmUK89,
I am impressed by the level of your interest and your depth of understanding of diamond cut quality and light performance. And thank you for referencing my article on 60/60 diamonds.

I think you would very much enjoy reading Al Gilberson’s fascinating book on the history of diamond cutting (American Cut- The First 100 Years). It reveals the reasons that diamonds have been traditionally cut for weight rather than beauty. That trend stubbornly persists in the market today, despite technologies available to consistently deliver more beautiful diamonds to the market. Other reviews of Al's book are searchable here on pricescope, and my review can be found at: https://www.whiteflash.com/about-di...st-100-years-book-by-al-gilberson-gg-1539.htm

When GIA finally came out with their cut grading system in 2005, round diamond cutting started becoming a whole lot better. The GIA system provides some reasonable guidelines that help consumers narrow down diamonds for consideration, in a manner very similar to the HCA. Because of the global reach of GIA, this was a highly impactful and positive development that greatly benefits the consumer, and as such, the whole market.

However, the idea that the GIA cut grading system is ‘more respected’ than the system developed by AGSL is a complete mischaracterization, as you rightly pointed out. And I am happy to see that Rockdiamond subsequently qualified his choice of words.

The AGSL system is the only one based on ray tracing of the actual diamond. This allows for the evaluation of not only the proportions, but of the angles and slopes of all the facets giving a holistic and comprehensive view of how the diamond is handling light.

You would be hard pressed to find anyone in the industry, regardless of their particular niche in the diamond trade, who thinks the technologically sophisticated and peer reviewed light performance grading system of the AGSL is ‘less respected’ than the table-based GIA system.

 

[Rockdiamond]

What I said was the GIA is more "widely respected".
I don't think there's any debate there- GIA is known by exponentially more people, that in turn, respect it.
Actually, there are MANY people in the trade who feel AGSL is off base in their cut grading system.
The princess cut grade is a perfect example.
Cutters ran away from it in droves.
To illustrate this: there are 644 AGSL princess cuts on rapnet.
By contrast there are 57,591 princess cuts with GIA.
Popularity does not make GIA "better"- but the reasons why it's so much more popular are important in this discussion.
Sellers that offer AGSL are bound to be protective of it- and well they should.
I'll make TerxasLeaguers case here- the 644 princess cut diamonds on rapnet are likely far better cut than the average stone from the GIA group.
But they're all cut to a similar standard- and that's part of the issue. It's just too narrow.
There are some remarkable cut designs that just don't fit into the AGSL design mold.
Like a Radiant cut.
If a cutter wants to cut a princess with good spread, lower contast greater scintillation, AGSL won't be the place to grade it because they would downgrade the cut on factors not related to what people love about the appearance of the diamond.
This is not a knock on AGSL princess cuts- they're awesome- they just should not be held up as the "Standard"
Same for rounds.
For sure there are cutters who prefer a wider grade so they can take advantage- probably most cutters that want a wider grade.
But not all. I personally know cutters who's main interest is great cut who were never able to find the sweet spot in AGSL cut grading because it's based on principles that do not stand when broadly extrapolated- like a smaller table being better "mathmatecally".

The long story I wrote above touches on this problem.
If a seller can convince people that the type of ideal cut diamonds they sell are demonstrably "better" they can get the higher prices.
If they can convince others on the forum to spread that "gospel" they don't even have to work at it anymore. If they can convince others to attack anyone who might disagree so much the better.

AS we're discussing this here we can see that 60/60 is NOT a culprit in cheating consumers out of yeild.
TexasLeager- the 60/60 page on your site that gm89uk linked to is totally misleading in that regard.

 

[Texas Leaguer]

Cutters did not run away from cutting ideal princess cuts. Most never were there to begin with! If GIA would ever come out with a cut grading system that would reward cutters for improving cut quality of princess, you would see the same kind of movement in a positive direction that we saw when GIA introduced cut grading for rounds.

The AGSL system is not designed to convince people of a particular style of cutting. It is designed to measure the output of different designs and executions. The methodology of the measurements has been peer reviewed by the scientific community. There is no doubt that the foundational concepts are sound. Just because princess have generally been cut flat and shallow since the princess was first introduced into the market in the 1960s, in no way proves it is the best way to cut them. AGSL demonstrated how you can get more of what makes a diamond beautiful by cutting a princess with a little more depth and a fuller crown.

Of course, it requires more time, more skill, and more rough to make an AGS Ideal. If the broad market is not demanding more, manufacturers will give less. And that market reality explains the current status quo. GIA is the big market mover. AGSL has limited ability to move the needle in a broad sense. AGSL has, however, been influential in shedding light on the importance of design and craftsmanship to the optical value factors that are ultimately of most importance to consumers. And the emergence of AGSL in the 1990’s with their reporting on cut quality and the interest in the consumer market that was created, represented a significant factor in the GIA coming out with their own cut grade system (albeit a long 10 years later). Competition is always good for the consumer!

 

[Rockdiamond]

If the AGSL Princess Cut had real advantages or was more attractive to more buyers, the disparity would not be nearly as great.
I agree that AGSL is not trying to "convince" people of anything. That's up to sellers. And here on PS, other people who buy into the theory.
The true issue is the promotion of AGSL here on PS rather than AGSL itself.
60/60 is fine by AGSL, but not apparently by the "Paul" who's "ideal proportions" are the basis of this discussion. Or by your company Texas Leaguer- based on your 60/60 page for example
The opposite of "widely respected" is "more narrowly respected"
That means no one ( at least not me) is saying AGLS does not have a well respected system.
The technology involved in the AGSL system of cut grading is indeed impressive- but it's not an "end all" that makes other methods of assessment invalid.
In my opinion- and many others in the trade I've spoken with- AGSL is just too restrictive.
Another thing coming from this thread is that for sure, there are cutters who are cutting deeper diamonds with greater yield and getting AGSL0- it's not just GIA that gets gamed.
Like Pauls system- eliminating diamonds more shallow than 61.5% benefits some cutter's yeilds

 

[Texas Leaguer]

David,
If you are going to say things like : "TexasLeager- the 60/60 page on your site that gm89uk linked to is totally misleading in that regard." please have the courtesy to support your position.

I don't feel there is anything misleading in that article,and if there is I would be keen to correct it.

 

[Rockdiamond]

Thank you Bryan- I know that's the case.
Start with the picture labeled "Extreme examples of poorly proportioned 60/60 diamonds"
Can you honestly say you've ever seen a diamond cut like one of those?
There is an explanation further down explaining 60/60 can earn EX and 0. But not close enough to the CG diamonds.
Furthermore, as this thread highlights, today's 60/60 triple EX or AGSL0 cut grade diamonds are likely to have better spread- potentially lower yield than Tolk
Maybe- just maybe- we could have made a case 45 years ago that 60/60 was being abused by cutters to sell badly cut stones. But at the same time the stones cut by Winston- and others- were cutting amazing 60/60's. Those- and today's super well cut 60/60's clearly rival today's "Super Ideal"

If the point was- you can't just use table/depth to determine cut quality, then we're on the same page.
So why even bring 60/60 into it?

 

[Texas Leaguer]

Thank you Bryan- I know that's the case.
Start with the picture labeled "Extreme examples of poorly proportioned 60/60 diamonds"
Can you honestly say you've ever seen a diamond cut like one of those?
There is an explanation further down explaining 60/60 can earn EX and 0. But not close enough to the CG diamonds.
Furthermore, as this thread highlights, today's 60/60 triple EX or AGSL0 cut grade diamonds are likely to have better spread- potentially lower yield than Tolk
Maybe- just maybe- we could have made a case 45 years ago that 60/60 was being abused by cutters to sell badly cut stones. But at the same time the stones cut by Winston- and others- were cutting amazing 60/60's. Those- and today's super well cut 60/60's clearly rival today's "Super Ideal"

If the point was- you can't just use table/depth to determine cut quality, then we're on the same page.
So why even bring 60/60 into it?

The point of the first graphic is to illustrate the fallacy of the old assumption that 60/60 necessarily indicated a well cut diamond. You can arrive at that combination via some very unflattering routes. The graphic shows the extremes.

There is nothing in the article to refute your assertion that the stones cut by Winston were great 60/60's. They could even have potentially been AGS0.

But implicit in the narrow range of proportion sets with the potential to make a 60/60 Ideal is the fact that faceting precision would be critical. That is, the ray tracer evaluates the totality of the facets in three dimensions and can't be gamed like a chart-based grade assignment that pegs a grade based upon averaged and rounded measurements.

 

[Rockdiamond]

Bryan,
It's, of course, your right to present information as you see fit- and in fairness, there's a lot of details below the fold. It's clear you want to be informative.
We just see things differently.
For example, in my experience, the best cut goods in the '70's and '80's were 60/60- that's NOT a fallacy.
Badly made goods then, and now are generally NOT 60/60. Back then they were usually heavy Indian makes- 63+ depth. Flat stones as well- but not nearly as many as heavy stones.
The only other stones which were seen as competition were the LK Ideal stones.
In the '80's I was working for M Fabrikant, at the time one of the world's largest polished dealers- "Russian" makes were the best of the best at the time. They were 60/60's
Every bit as nice as any Ideal Cut.
Facet precision on stones designed like the Winston 60/60 was geared towards scintillation - less towards contrast and patterning ( H&A) So it's not going to look pretty in a reflector- but it was not designed to look pretty in a reflector, it was designed to look good in real life.

 

[Dancing Fire]

We need to see a side by side video of David's best 60/60 vs ACA...

This argument have had been going on for yrs...

 

[Rockdiamond]

Yes it has DF ( mr "fan the flames")

But truthfully, a lot has changed.
gm89uk has raised issues that caused me to look again at how the market has reacted- and the change over the past 10 years is dramatic.
DF- can we just agree that whatever that totally horrible diamond you had recut into a gem was NOT anything like the 60/60's cut at Harry Winston in the '70's?
I'm not saying there are no badly cut 60/60's just that many are very attractive.
And now, they are certainly a ....delicacy.
Bryan there's a statement on the page under discussion about Tolkowsky demonstrating mathematically the benefits of smaller tables. I am not familiar with the statement he made, and if it specifically regarded 60% as "large"
I love science- I worship science. But I don't see a way you could ever prove mathematically that 57% is better than 60%, for that reason alone.
You can certainly achieve sufficient crown height to achieve an AGSL 0 at 60% table- that aspect is mathematically provable using AGSL numbers.

The whole premise that "back in the old days" someone would take the effort to get to 60/60, yet still cut a bad looking diamond on purpose doesn't really hold water. They'd want to cut deeper to maintain weight.

 

[Garry H (Cut Nut)]

We need to see a side by side video of David's best 60/60 vs ACA...

This argument have had been going on for yrs...

David are you up for it?