Experts needed on Diamond Proportions.

[Rockdiamond]

This is a very important issue to many of us- I am sorry the discussion took a contentious turn.
I have nothing but respect for all the tradespeople who have posted in this thread.

In a strict business sense: Say all the high quality honest sellers here on PS were able to sell a broader range of diamonds.
This would lead to more satisfied buyers- for any of the popular sellers here on PS.
Illustrating the benefit of carefully selected, value priced, "second tier" cuts will not damage the image or sales of CBI, or ACA or other premier cuts- it will simply include more people in the discussion IMO.

Peace

 

[Dancing Fire]

Light performance= preference.
Period.
There's no such thing as "better light performance" other than a persons preference.
Even if ray tracing/aset/is can tell us which diamond returns more light in theory, there is no workable calibration to tell us which diamond returns more light in the real world- and even if there was, returning more light in and of itself does not make a diamond more desirable, or better cut. Mirrors return more light than diamonds..
In terms of the dirt aspect- it the size and placement of the facets on the pavilion that causes a different light performance- not better, different.
This has to do with physics and changes how a diamond looks when there's gunk on the pavilion.
Changing from EX to VG will have ZERO affect on how the diamond looks when dirty for that reason alone.

Really David??...who would spent thousands of $$$ on a DUD?..

 

[KobiD]

Really David??...who would spent thousands of $$$ on a DUD?..

Define dud?

Just watched a comparison video by GOG "Comparing two GIA Ex/AGS Ideal diamonds to a GIA very good". There are visible differences between them indeed, but to call the VG a dud is a bit of a long shot.

Who would spend thousand of dollars on a rock?

Whats the problem with offering 2nd tier, decent performing stones, if the price relfects it? I think most vendors do just this, but most buyers who end up here either decide themselves that they want the Ideal spec stones, or get lead to believe that their specific choice will be a dud if its not the cream of the crop.

 

[Rockdiamond]

Kobi- you ask a good question - what's the problem with carrying VG cut grade stones?
Actually a few:
1) almost no sellers actually "carry" diamonds- they sell off lists.
2) consider Internet sales. Increasingly people come to PS if they're shopping online.
If you read this thread you quickly learn VG cut is frowned upon here. IMO it's an issue of how the subject is discussed. I'm attacked for having this opinion- which makes it hard to have an objective discussion.
But the bottom line is that no one is suggesting considering VG cut grades making them more difficult to sell overall. This reduces the price making them even more attractive.
I honestly feel that the industry and consumers alike will benefit from more diversity in this area.

 

[Texas Leaguer]

Consumers do not need the internet or pricescope to find mediocrity in the cut quality of diamonds. It is all around them in the traditional jewelry world. In fact, the philosophy that diamonds should be cut for less than their full beauty potential is why there is such 'diversity' in the market with regard to this most important characteristic. The real question is why that should even be the case.

Cutting a diamond for weight is like selling an SUV body with a small engine. You end up with what looks like other SUVs on the surface but it has insufficient power. Better that the same engine be put in a sports car, then you have the performance that you want.

I encourage all tradespeople and even diamond enthusiasts to read Al Gilbertson's excellent book "American Cut - the first 100 years" for background on how we came to be where we are today. There were a few voices strongly advocating the philosophy that diamonds should be cut for beauty. But the market continued to be drawn in another direction. For a hundred freaking years!

Fortunately, the advocates of the old philosophy are finally starting to be supplanted by a new generation of consumers who want better. But that does not keep those still rooted in the past from relentlessly banging their fist on the table to try to preserve outdated notions.

 

[Paul-Antwerp]

Rockdiamond,

With all due respect, you seem to be inventing a non-reality. In the world-market, internet-sales are still a small portion of sales, and in the area of internet-sales, PS only has a minor impact on the total. Compared to the world-market of diamonds, you are grossly exaggerating the impact of this forum and its contributors.

Still, in that world-market of diamonds, we see the majority of GIA-graded stones nowadays carrying an EX cut-grade. Not PS, not the Internet, but the world-market of diamonds is frowning upon VG cut-quality.

This has a number of effects.
- The world-market being content with the EX-grade as such leads to a majority of GIA-EX-stones cut to the higher weight-retention-area, lower performing area, within GIA-EX. Easily 80% of GIA-EX are near the bottom-level, very close to GIA-VG.
- With GIA-theory just being theory, there probably is no difference between many GIA-VG and that 80% of GIA-EX, with regards to performance.

I constantly see dozens of 'diamond professionals' like yourself, so entrenched in that basic market of 'low GIA-EX', often selling entire businesses of hundreds of such stones purely on paper without ever looking at a stone, not at all understanding what light performance is about, wondering why on earth one would reject or prefer one GIA-EX over another, definitely not accepting any of the science often discussed about on PS. In that sense, you are not alone. But knowledge is not decided by a democratic vote, I fear.

Live long,

 

[Rockdiamond]

HI Paul,
As I mentioned earlier- this is a rather hot button topic, and I would hope we can discuss it without hostility.

Re PS, and the internet's affect on the world diamond market as a whole:
I don't believe there's an accurate relevant method to determine exactly the effects of the last 10 years of internet diamond sales has had on brick and mortar retail diamond sales. Are we speaking of number of carats, number of stones, dollars sold?
My position, here in NYC gives me a different perspective than yours in Antwerp.

Based on my experience, the American retail diamond market has been completely upended due to internet sales.
My job used to be on the road sales- the number of strong retail diamond outlets is not half of what it was in 1998.
I have not studied the major players ( Zales, Kays etc) - but it would seem a few have have been able to maintain market share to some extent. Based on what I've seen in the mall, these places do sell mediocre diamonds. Graded by IGI, or EGL- or no one. There's a lot of volume there- and I agree there's a lot of badly cut goods on the market.

Independent diamond retail sellers that used to sell high quality GIA or AGSL graded stones?
They still exist, but their numbers have been decimated.

How many people buy any $10000 item today and don't look online?

Now if we consider the internet as a whole, and PS effects on it: Maybe I live in a bubble- but it seems to me that many English speaking buyers of "boutique diamonds" will find PS. That includes super ideal diamonds, fancy colored diamonds, etc
So- it may not affect the entire world market, but I do believe that PS has had an effect on US diamond sales of costly stones- say, over $3000.


My experience is that diamonds sell, in large part, based on their physical attributes.
Not their "performance" - but their beauty.
Of course I understand you see this aspect differently- it's a big world and everyone may have their opinion.

About the "diamond professionals" you're speaking of.
I know quite a few professionals in my field.
I don't speak to any that sell hundreds of GIA graded stones and never look at them.
Years ago, maybe.
In any event, I've never sold a diamond I have not personally inspected.

I understand the science behind "performance" ( my turn for quotes).
My goal is beauty.
That is really what I strive for in the diamonds we buy, and pieces we make.
I agree that there's buyers who want the scientific data you speak of- and I completely understand why. In some cases it due to the beauty of a well performing stone using your definiton- in other cases it's because they read that's what they need.

As before
Peace

 

[Dancing Fire]

My experience is that diamonds sell, in large part, based on their physical attributes.
Not their "performance" - but their beauty.
Of course I understand you see this aspect differently- it's a big world and everyone may have their opinion.

David
How can a diamond be beautiful w/o performance?..

 

[Rockdiamond]

OK- try it this way DF
Performance = beauty

Define each.
now you know what kind of a stone performs for you.

I've never seen it personally, but based on the others I've seen, I have no doubt your Octavia is awesome- regardless if we're talking about performance or beauty. I'm a step cut lover, and the Octavia's I've seen blew me away.
I loved them.
But you have to realize that there's other people who love other types of diamonds, that will not agree.

Neither is wrong.
No matter how well a stone performs the recipient needs to love the way it looks.

 

[Dancing Fire]

No matter how well a stone performs the recipient needs to love the way it looks.

Ok David ...let me ask you this Q.
Have you ever had a customer who rejected a stone b/c it sparkles too much?

 

[Rockdiamond]

Yes- if they wanted a step cut. Step cuts glitter.

 

[pfunk]

No matter how well a stone performs the recipient needs to love the way it looks.

Ok David ...let me ask you this Q.
Have you ever had a customer who rejected a stone b/c it sparkles too much?

I've been following this thread closely as it interests me to see members of the trade discussing these things. Let me ask a question similar to what DF is asking, but a little different.

David, do you ever line up stones of similar color, clarity, and size but different in cut and allow the consumer to simply choose which looks best to them? For example, a GIA excellent next to some GIA very good/good cuts. If this is done, how often does a consumer choose the one with the lower cut grade?

 

[WinkHPD]

Really David??...who would spent thousands of $$$ on a DUD?..

Define dud?

Just watched a comparison video by GOG "Comparing two GIA Ex/AGS Ideal diamonds to a GIA very good". There are visible differences between them indeed, but to call the VG a dud is a bit of a long shot.

Who would spend thousand of dollars on a rock?

Whats the problem with offering 2nd tier, decent performing stones, if the price relfects it? I think most vendors do just this, but most buyers who end up here either decide themselves that they want the Ideal spec stones, or get lead to believe that their specific choice will be a dud if its not the cream of the crop.

I tried this for a while with my Value Select line. It did not work at all for me and I finally blew most of them out the door but still have a few on my site. When, and if, they ever disappear, they will not be replaced. My clientele want only the best and people who are not my clientele are all looking elsewhere for the Value Select type stones.

I will stick with what I both know and am known for. It works well for me. I actually think part of the reason I did not do well with the Value Select is that I always felt I was not doing my best for a client when I let them buy a stone I would not want to own for myself. I confess, I am a cut aficionado, and I truly believe that the top cuts are better and the lesser cuts are lesser. Many, such as my friend Rockdiamond disagree, but fortunately, we can still be friends.

Wink

 

[Dancing Fire]

Really David??...who would spent thousands of $$$ on a DUD?..

Define dud?

For MRBs?
Big table with a low crown.
Spready pancake stones with a low crown.
Have never met a stone that I'd love with a low crown.

 

[Rockdiamond]

No matter how well a stone performs the recipient needs to love the way it looks.

Ok David ...let me ask you this Q.
Have you ever had a customer who rejected a stone b/c it sparkles too much?

I've been following this thread closely as it interests me to see members of the trade discussing these things. Let me ask a question similar to what DF is asking, but a little different.

David, do you ever line up stones of similar color, clarity, and size but different in cut and allow the consumer to simply choose which looks best to them? For example, a GIA excellent next to some GIA very good/good cuts. If this is done, how often does a consumer choose the one with the lower cut grade?

I've been following this thread closely as it interests me to see members of the trade discussing these things. Let me ask a question similar to what DF is asking, but a little different.

David, do you ever line up stones of similar color, clarity, and size but different in cut and allow the consumer to simply choose which looks best to them? For example, a GIA excellent next to some GIA very good/good cuts. If this is done, how often does a consumer choose the one with the lower cut grade?

I have to tell you, LOVE your handle pfunk!!

To answer the part in bold:
Generally not, but for a few main reasons
1) We do not carry many "regular" round diamonds. The last round we sold was last week, it was a Y-Z color.
The stone was amazing
And it was a VG cut grade. There was nothing at all "mediocre" about this diamond.

Since such stones are super rare, there was no possibility of a comparison.
2) The vast majority of our clients do not visit the office- rather buy online.

Of course I've done many side by side comparisons.
Just like there's different flavors of Fancy Shaped diamonds, there's different flavors of rounds- and people that love diamonds tend to have preferences.

About 4 years ago I gave my wife a near colorless round diamond.
She picked a 60/60 EX cut grade- and she's seen many super ideal diamonds. The stone she picked would surely get panned here on PS.
She loved it- its since been traded in ( my wife has an unrestricted trade up privelidge )

 

[kb1gra]

For what it's worth, I had a lovely experience shopping in person with David and in fact did compare a number of stones together. The one I liked the best was one that also would I'm sure fail the PS test...a Daussi cushion.

We all have our niches in the business, be it superideals or cushion cuts or colored stones. One may be antithetical to the goals of another.

 

[Rockdiamond]

Really David??...who would spent thousands of $$$ on a DUD?..

Define dud?

Just watched a comparison video by GOG "Comparing two GIA Ex/AGS Ideal diamonds to a GIA very good". There are visible differences between them indeed, but to call the VG a dud is a bit of a long shot.

Who would spend thousand of dollars on a rock?

Whats the problem with offering 2nd tier, decent performing stones, if the price relfects it? I think most vendors do just this, but most buyers who end up here either decide themselves that they want the Ideal spec stones, or get lead to believe that their specific choice will be a dud if its not the cream of the crop.

I tried this for a while with my Value Select line. It did not work at all for me and I finally blew most of them out the door but still have a few on my site. When, and if, they ever disappear, they will not be replaced. My clientele want only the best and people who are not my clientele are all looking elsewhere for the Value Select type stones.

I will stick with what I both know and am known for. It works well for me. I actually think part of the reason I did not do well with the Value Select is that I always felt I was not doing my best for a client when I let them buy a stone I would not want to own for myself. I confess, I am a cut aficionado, and I truly believe that the top cuts are better and the lesser cuts are lesser. Many, such as my friend Rockdiamond disagree, but fortunately, we can still be friends.

Wink

A most valuable asset- a friend.
We agree on that part 100%

Your post shows why you're successful.
We both share a 40 year old passion for the stones.
We were both weaned on a different type of cut ( 60/60's of yore)
We were both around when Lazaare Kaplan started cutting "Ideal Cut" diamonds.
When I fist started looking at LK Ideal Cuts, I thought the 57% tables looked way too small.
I grew to love that type of stone as well.
I think part of our different outlook is my continued love of the slightly spreadier stone.
And thankfully we can share this difference in opinion the way we have.

I stand by my statement that I respect every tradesperson who's posted here.
Every company represented here by these tradespeople is an outstanding example in our business.
I regret any sort of negativity this has caused- yet it's an important discussion, and worth having.

About a second tier value line.
If a comparison was to be made, maybe it should be what their money buys.
Instead of lining up 2 stones of similar color, clarity and weight but different cut qualities, what if we compare stones of the same cost, with different sizes due to differences in cut.
If there was a 20% difference between a VG and an EX, compare the 1.20ct VG to a 1.00ct EX

I am not arguing against the 1.00 EX as the better choice.
I know many people will take that route- and it's a great choice.
I AM saying that comparison that ignores size- or the possibility that a given buyer prefers a stone that "does not perform to 100%" according to AGSL scientific standards is not a benefit to the buyers in a broad online discussion.
If we're going to educate, context is extremely important

I'm not advocating mediocre anything.

 

[Paul-Antwerp]

HI Paul,
As I mentioned earlier- this is a rather hot button topic, and I would hope we can discuss it without hostility.

My position, here in NYC gives me a different perspective than yours in Antwerp.

As before
Peace

Hi David,

No hostility at all, and while I must admit that the NY-experience in most fields and in general has more value than the small-town-experience of Antwerp, you must agree that in diamonds, the NY-perspective is close to meaningless compared to the Antwerp-perspective.

Live long,

 

[blackprophet]

HI Paul,
As I mentioned earlier- this is a rather hot button topic, and I would hope we can discuss it without hostility.

My position, here in NYC gives me a different perspective than yours in Antwerp.

As before
Peace

Hi David,

No hostility at all, and while I must admit that the NY-experience in most fields and in general has more value than the small-town-experience of Antwerp, you must agree that in diamonds, the NY-perspective is close to meaningless compared to the Antwerp-perspective.

Live long,

And to build on this (and a point Wink made which you glossed over): Could you (RD) give a step by step process to find a VG stone that is beautiful totally online without coming into your shop? If you are advocating that people on PS should suggest VG stones, a process to do that needs to be laid out. Because finding those stones seem to be hard without seeing them in person. The prosumers here are working remotely with people looking for stones in inventories they don't have access to, so they are suggesting stones that have the best chance of being beautiful. From the discussion and from what I've seen, its not upselling. Its ensuring buyers get quality for their money.

If you can give them a way to find those VGs in that circumstance, I think the board would be better for it, and you would give to potential buyers more choice. I'm sure not everyone would add it to their repetoir, but some would.

 

[Rockdiamond]

HI Paul,
As I mentioned earlier- this is a rather hot button topic, and I would hope we can discuss it without hostility.

My position, here in NYC gives me a different perspective than yours in Antwerp.

As before
Peace

Hi David,

No hostility at all, and while I must admit that the NY-experience in most fields and in general has more value than the small-town-experience of Antwerp, you must agree that in diamonds, the NY-perspective is close to meaningless compared to the Antwerp-perspective.

Live long,

Thank you very much Paul- this post means a lot to me.
I can say without hesitation that I've never seen stone cut better than the ones you do- and any of our clients that own a CBi have been over the moon ecstatic with their purchase.

Your point about the different markets, and how it affects our outlook is spot on as well.
I've only been to Antwerp once buying diamonds, but as compared to the New York experience, it could not have been more different.
I loved your town- it's an amazing place.
NY is far less reserved which is both positive and a drawback. Like everything else.

 

[Rockdiamond]

HI Paul,
As I mentioned earlier- this is a rather hot button topic, and I would hope we can discuss it without hostility.

My position, here in NYC gives me a different perspective than yours in Antwerp.

As before
Peace

Hi David,

No hostility at all, and while I must admit that the NY-experience in most fields and in general has more value than the small-town-experience of Antwerp, you must agree that in diamonds, the NY-perspective is close to meaningless compared to the Antwerp-perspective.

Live long,

And to build on this (and a point Wink made which you glossed over): Could you (RD) give a step by step process to find a VG stone that is beautiful totally online without coming into your shop? If you are advocating that people on PS should suggest VG stones, a process to do that needs to be laid out. Because finding those stones seem to be hard without seeing them in person. The prosumers here are working remotely with people looking for stones in inventories they don't have access to, so they are suggesting stones that have the best chance of being beautiful. From the discussion and from what I've seen, its not upselling. Its ensuring buyers get quality for their money.

If you can give them a way to find those VGs in that circumstance, I think the board would be better for it, and you would give to potential buyers more choice. I'm sure not everyone would add it to their repetoir, but some would.

Excellent direction to take BP. That is exactly the type of goal that would allow a greater diversity of advice.
I will need to give it a bit of thought over the weekend.

 

[Rockdiamond]

For what it's worth, I had a lovely experience shopping in person with David and in fact did compare a number of stones together. The one I liked the best was one that also would I'm sure fail the PS test...a Daussi cushion.

We all have our niches in the business, be it superideals or cushion cuts or colored stones. One may be antithetical to the goals of another.

Hi kb,
Thank you very much for coming!

The Daussi stones are a great example of the type of cut that is slightly polarizing- and to me that's a good thing.
Some people love them and some people hate them- and with equal intensity!

 

[Garry H (Cut Nut)]

People are eager to compare the two labs and routinely ask which one is better.

This is a false dilemma. Although there's a fair amount of overlap in the top grades, they aren't answering the same questions.

I'm more of a physics sort of guy and I definitely like the AGS strategy but GIA does have a point. One of the assumptions in the AGS model is that the viewing environment is with one eye from directly over head with the light source also coming from directly overhead. This is not a 'real world' condition. Neil I think AGS's model is more complex and better than your simple explanation, but the fact that it is based on a single eye perspective is a flaw. e.g. I have bought and sold amazing emerald cuts where the head obstruction from one eye at a common viewing distances results in a bright facet (virtual facet) from the other eye. The worst grade on beuatiful emerald cuts (IMHO) is AGS7. On that basis alone, I call it aflawed system for anything other than a round diamond. (of course I am also well on the record that thier obstruction model is too harsh, again because of human stereoscopic vision) GIA doesn't get a free pass either. Their study was fundamentally measuring popularity, not performance. These are not synonyms. Popularity is of enormous interest to dealers who want to invest their money in things that are likely to sell quickly for them, but it's far more problematic for consumers trying to decide which one is 'best'.

GIA do not have a cut grading system, they have the equivalent of HCA as a rejection system, but they made a mess of their model too because of the limitations of their light box used with a flawed sample of 'popular observers' i.e. dealers. But GIA's system can never ever be rolled out for anything other than round cuts. so it is a rejection system, not anything like a beauty or performance system

 

[Garry H (Cut Nut)]

For what it's worth, I had a lovely experience shopping in person with David and in fact did compare a number of stones together. The one I liked the best was one that also would I'm sure fail the PS test...a Daussi cushion.

We all have our niches in the business, be it superideals or cushion cuts or colored stones. One may be antithetical to the goals of another.

Was the very large spread for its weight of that cut a big factor in your preference?

 

[Garry H (Cut Nut)]

This is a very important issue to many of us- I am sorry the discussion took a contentious turn.
I have nothing but respect for all the tradespeople who have posted in this thread.

In a strict business sense: Say all the high quality honest sellers here on PS were able to sell a broader range of diamonds.
This would lead to more satisfied buyers- for any of the popular sellers here on PS.
Illustrating the benefit of carefully selected, value priced, "second tier" cuts will not damage the image or sales of CBI, or ACA or other premier cuts- it will simply include more people in the discussion IMO.

Peace

Since my business is an oldfasioned B&M David, the most important thing I need to do is buy consistently magnificent diamonds at good value prices for my staff to sell. If they look at any diamond and think its a dud then i am stuck with a dog. Most of my rounds end up being H&A's simply because that is a default symmetry level for most of the manufacturers I work with. But its the realm of fancy shapes which my mettle is tested!

 

[Texas Leaguer]

People are eager to compare the two labs and routinely ask which one is better.

This is a false dilemma. Although there's a fair amount of overlap in the top grades, they aren't answering the same questions.

I'm more of a physics sort of guy and I definitely like the AGS strategy but GIA does have a point. One of the assumptions in the AGS model is that the viewing environment is with one eye from directly over head with the light source also coming from directly overhead. This is not a 'real world' condition. Neil I think AGS's model is more complex and better than your simple explanation, but the fact that it is based on a single eye perspective is a flaw. e.g. I have bought and sold amazing emerald cuts where the head obstruction from one eye at a common viewing distances results in a bright facet (virtual facet) from the other eye. The worst grade on beuatiful emerald cuts (IMHO) is AGS7. On that basis alone, I call it aflawed system for anything other than a round diamond. (of course I am also well on the record that thier obstruction model is too harsh, again because of human stereoscopic vision) GIA doesn't get a free pass either. Their study was fundamentally measuring popularity, not performance. These are not synonyms. Popularity is of enormous interest to dealers who want to invest their money in things that are likely to sell quickly for them, but it's far more problematic for consumers trying to decide which one is 'best'.

GIA do not have a cut grading system, they have the equivalent of HCA as a rejection system, but they made a mess of their model too because of the limitations of their light box used with a flawed sample of 'popular observers' i.e. dealers. But GIA's system can never ever be rolled out for anything other than round cuts. so it is a rejection system, not anything like a beauty or performance system

Hi Garry,
A few questions if I may. Could you expand your comments on the AGS obstruction model- how would you adjust it? Do you think the fact that AGS system does not account for stereo vision makes it generally more punitive or less? You call it a flawed system for fancies based upon your observations of emerald cuts - how would you characterize the system with regard to princess evaluation?

Love to hear your thoughts.

 

[Karl_K]

A few questions if I may. Could you expand your comments on the AGS obstruction model- how would you adjust it?

I am not Garry but the biggest problems are it only takes into account very close viewing, its hard obstruction where in the real world its soft, it is a round disk where in the real world it is not and it is only one distance.
I would start by taking into account 3 distances, do a study and get the average for half arm length, full arm length and close up viewing and the different degrees of obstruction.
Then use both hard and soft obstruction. Soft obstruction would also have to be several models as an average would be like a one size fits all glove that really fits no one well. Start with say 3.
Then in the tilt grading calculate a grade based on how quickly a VF moves in and out of obstruction with tilt with a large penalty for large virtual facets that do not flash in say 5 degrees tilt under hard obstruction.
Then do the same for direct and diffused lighting.

Doing two eye viewing simulations is probably beyond what is possible today in a cut grading system but eventually it should be taken into account.

hard obstruction is a solid disk of fixed color.(blue in ASET black in IS)
soft obstruction would be the shape, varied color and reflection of a human head and body.

 

[Karl_K]

You call it a flawed system for fancies based upon your observations of emerald cuts - how would you characterize the system with regard to princess evaluation?

Again not Garry.
I think it worked ok for princes cuts and resulted in some superb princess cuts being cut.
They work similar to rounds so it was a reasonably good match.
I believe that more optimizations is possible in princess cuts than the current AGS0 system allows.
However in at least one case the numbers on the report looked weird which lead to marketing problems even with the current ags0 and further optimization would make that problem worse.
Highly optimized princess cuts have numbers the market considers weird.

As far as emerald and SE the AGS system can recognize great ones but it can also miss them and its possible for the grade to be misleading both bad and good.
There are a lot of thing that make for a great EC/SE that the ags system simply does not take into account.

 

[Garry H (Cut Nut)]

People are eager to compare the two labs and routinely ask which one is better.

This is a false dilemma. Although there's a fair amount of overlap in the top grades, they aren't answering the same questions.

I'm more of a physics sort of guy and I definitely like the AGS strategy but GIA does have a point. One of the assumptions in the AGS model is that the viewing environment is with one eye from directly over head with the light source also coming from directly overhead. This is not a 'real world' condition. Neil I think AGS's model is more complex and better than your simple explanation, but the fact that it is based on a single eye perspective is a flaw. e.g. I have bought and sold amazing emerald cuts where the head obstruction from one eye at a common viewing distances results in a bright facet (virtual facet) from the other eye. The worst grade on beuatiful emerald cuts (IMHO) is AGS7. On that basis alone, I call it aflawed system for anything other than a round diamond. (of course I am also well on the record that thier obstruction model is too harsh, again because of human stereoscopic vision) GIA doesn't get a free pass either. Their study was fundamentally measuring popularity, not performance. These are not synonyms. Popularity is of enormous interest to dealers who want to invest their money in things that are likely to sell quickly for them, but it's far more problematic for consumers trying to decide which one is 'best'.

GIA do not have a cut grading system, they have the equivalent of HCA as a rejection system, but they made a mess of their model too because of the limitations of their light box used with a flawed sample of 'popular observers' i.e. dealers. But GIA's system can never ever be rolled out for anything other than round cuts. so it is a rejection system, not anything like a beauty or performance system

Hi Garry,
A few questions if I may. Could you expand your comments on the AGS obstruction model- how would you adjust it? Do you think the fact that AGS system does not account for stereo vision makes it generally more punitive or less? You call it a flawed system for fancies based upon your observations of emerald cuts - how would you characterize the system with regard to princess evaluation?

Love to hear your thoughts.

Bryan I agree with Karl, on both obstruction and binocular vision. Interesting though is that Peter Yantzer explained to me that the leakage patch in the center of many princess cuts disappears with close up stereo vision. One eye sees a bright area and the other eye sees a bright area in the opposing sides - check it. But from further away many stones still show the leakage, so their overly close model does not work always!

 

[John P]

Edited. See next page.