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Gia Excellent Cut


AverageJoe
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Hi,

 

I've recently had a debate with a friend with regard to the GIA cut grades, specifically the 'excellent' cut grade. My point that it is too wide a range with regard to angles etc... for it to be really be a useful classification system. He countered that the GIA inspect diamonds for visual beauty with their eyes too; not just measure it with protacters and a slide-rules. He also countered the GIA represent a number of different tastes that appeal in different locales and to different age groups. He said I need to drop my parochial school view of diamonds and broaden my horizons to a wider global picture of diamond beauty. This quite naturally insensed me. He likened it to some people like dressing in loud bright clothes others prefer more conservative sober apparel. He went on further that light performance whilst important, has to be examined with reference to the way our eyes see preceive light. He said diamond needs to display contrast i.e. lighter and darker areas otherwise we'd all buy light bulbs. He went further and said only a very small minority of diamonds certified by The GIA receive the 'Excellent' rating whilst the majority receive 'Good'. He said that 'Excellent Cut' meant excellent but that the person viewing the diamond should decide if that is the 'look' of diamond they prefer. He said it's like painting some like impressionists and others expressionist. He said diamond cutting is an art not a science. As he said appealing to once senses and heart not one's brain with numbers...What's your take on it?

 

Auberry

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The GIA cut grade is strictly based on measurements although they do use some petty clever tools to get the measurements. There are no protractors or slide rules involved. The only human judgment that goes into it are the finish grades for polish and symmetry.

 

GIA doesn’t release the statistics on how many of the stones they grade are ‘excellent’ but anecdotal evidence and personal observation suggests that it’s huge. There was a discussion about this topic in this thread.

 

http://www.diamond.info/forum/index.php?sh...c=4152&st=0

 

I do agree that there’s a huge element of taste to diamonds and that it’s important as part of the shopping process. There is no ‘best’ cut and what one person likes the most will not be the same as what the next person likes.

 

Neil

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Good point Neil- But I do believe alot of human observation was incorprated into determining which measurements are included in the top cut grade.

 

I'm confident in my answer. Human observations were used in determining the formula but they are not part of the lab grading process. What the grader 'likes' plays no part (and it shouldn't). Even things like the rules regarding brillianteering are spelled out in the lab although they only appear on the report if they are used to downgrade a stone. It is not a function of a graders judgment.

 

Neil

Edited by denverappraiser
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I agree with most of what he says. Although some excellent cut grades look better than others and we can verify it with light performance analysis as well. Same goes with the AGS ideal cut grading system. Each stone is individual. They do make it kind of broad on the grades or there wouldn't be many ideal or excellent cut grade stones out there to purchase.

I feel if I'm going to pay a premium for a stone like that, I would want additional info on the individual stone to make sure I'm getting my money's worth.

 

That is where these technologies come in:

www.gemex.com

www.isee2.com

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Hi,

 

It's an interesting debate. Science versus art. I don't recommend people buy on just paper cut grades or proportions but actually view a range of diamonds to make a choice. I also admit I like the reassurance offered by science as it appeals to my rational side, my brain has something to compute to say yes it's good. My eyes say yes it good purely on an emotional level. With both sides sated, it's happy days. The visual emotional input people used to make seems to be on the wane with the move to online diamond purchases. I have nothing against purchasing a diamond online but I would always advise people to buy three (even if they have to use a credit card) and then keep the one they most like and return the others.

 

To throw another spanner in to the works what about the end-user. For example I appreciate a gourmet chief has extremely sensitive taste buds to pick out the flavours inherent in a gourmet dish, like person who create's fine perfumes has an extremely sensitive nose able to pick out the subtleties of the perfume. On most people these would be wasted as they don't have the sensitivity to really appreciate it. Like a rich man who buys a Monet just because it's a Monet and it satisfies his ego. If laid out 10 AGS 0 'Ideal' cut, 10 class 1 cut and 10 class 2 cut diamonds with identical inclusions, carat weight and colour could the man on the street actually sort them out in to the three cut categories with just his eyes? May their money would be better spent on increasing the carat weight or the colour of diamond and keeping the cut rating at AGS 2. I wonder whether the push for the end customer to get 'Ideal' cut diamonds is not making the best use of their money? Is the average man in the street being duped into buying something that only a diamond conniseur will truly appreciate? Has the law of diminishing returns kicked in at AGS cut 2. I wonder whether the GIA have taken the best path with getting a cross-section of people with varying sensitivities to diamond beauty to help sculpt their cut grading system. Did AGS get caught taking too much of a numbers/scientific approach with involving peoples visual perception of diamonds?

 

Jan if we have to use a Gemex or other machine to point out the difference in quality of diamond then does the difference really matter? I'm not being critical as I too like to have the reassurance that science can provide to my brain? Or is this just a way of saying mines better than yours? Is this science just to a way to pander to our egos? I'm just wondering whether we are beginning to lose sight of what it's all about, the visual, emotional, visceral perception of beauty? When you see a beautiful diamond in front you just flash it's charms.

 

Auberry

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If laid out 10 AGS 0 'Ideal' cut, 10 class 1 cut and 10 class 2 cut diamonds with identical inclusions, carat weight and colour could the man on the street actually sort them out in to the three cut categories with just his eyes?

 

This is remarkably close to what the GIA study in 2006 consisted of. They took a bunch of stones that were similar in size, color and clarity and that they otherwise knew quite a bit about (70 stones I think), showed them to observers in lots ranging from 2 to 5 stones and asked them to force rank them in order of preference. They would then show a different set of stones and repeat the test with both the same and different users under a variety of lighting conditions. They kept careful notes and repeated this over the span of several months using hundreds of observers, some making hundred of observations each. Overall they collected and cataloged hundreds of thousands of observations. Some of the people were employees and presumably experts and some were just folks they came across. A bit of number crunching later they found that certain stones were consistently more popular than others and they identified some sets of attributes that seem to do well. This may seem obvious but it’s worth noting that there were no stones that everybody loved and none that everybody hated. That’s where the taste issues come in. ‘Most popular’ is not the same as ‘best’ and it's not possible to rank the stones from 1-70 in a way that everyone would agree with. The solution was to divide them into 5 general categories and named them excellent, very good, good, fair and poor and made a range of computer models to describe each. Stones that are most similar to something the study called excellent will be graded as excellent, stones that are similar to ones that hardly anyone liked are poor etc. The dividing lines between the categories is, by definition, arbitrary arguable but it makes sense to only have 4 such lines instead of 69.

 

This is very different from the 2004-5 work by AGS. They did exhaustive raytracing on computer models of stones trying to get the theoretically optimum optical effect, including light return and the contrast issues that your friend mentioned. They then cut actual stones and studied them to decide if they were getting the results they wanted. From here they did a similar system of creating 11 grades and a set of parameters to define each one. Here the objective really was to define which one was 'best' and consequently which ones were almost as good or far away from their 'ideal'. They too discovered that there was no one answer to their question but rather different combinations of parameters that came to the same results.

 

They are completely different approaches and neither one addresses the question of what will be most beautiful to YOU or your beloved. That's because this is an impossible task. Critics of GIA object that it's overly broad and so inclusive as to be meaningless as a selection tool. Critics of AGS object that it's overly specific and that it misses the entire point ... beauty is in the eye of the beholder, not in a computer model. Both sides have valid points and, in the end, it's up to the consumer to decide which one, if either, they want to give more weight.

 

Neil

Edited by denverappraiser
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If laid out 10 AGS 0 'Ideal' cut, 10 class 1 cut and 10 class 2 cut diamonds with identical inclusions, carat weight and colour could the man on the street actually sort them out in to the three cut categories with just his eyes?

 

This is remarkably close to what the GIA study in 2006 consisted of. They took a bunch of stones that were similar in size, color and clarity and that they otherwise knew quite a bit about (70 stones I think), showed them to observers in lots ranging from 2 to 5 stones and asked them to force rank them in order of preference. They would then show a different set of stones and repeat the test with both the same and different users under a variety of lighting conditions. They kept careful notes and repeated this over the span of several months using hundreds of observers, some making hundred of observations each. Overall they collected and cataloged hundreds of thousands of observations. Some of the people were employees and presumably experts and some were just folks they came across. A bit of number crunching later they found that certain stones were consistently more popular than others and they identified some sets of attributes that seem to do well. This may seem obvious but it’s worth noting that there were no stones that everybody loved and none that everybody hated. That’s where the taste issues come in. ‘Most popular’ is not the same as ‘best’ and it's not possible to rank the stones from 1-70 in a way that everyone would agree with. The solution was to divide them into 5 general categories and named them excellent, very good, good, fair and poor and made a range of computer models to describe each. Stones that are most similar to something the study called excellent will be graded as excellent, stones that are similar to ones that hardly anyone liked are poor etc. The dividing lines between the categories is, by definition, arbitrary arguable but it makes sense to only have 4 such lines instead of 69.

 

This is very different from the 2004-5 work by AGS. They did exhaustive raytracing on computer models of stones trying to get the theoretically optimum optical effect, including light return and the contrast issues that your friend mentioned. They then cut actual stones and studied them to decide if they were getting the results they wanted. From here they did a similar system of creating 11 grades and a set of parameters to define each one. Here the objective really was to define which one was 'best' and consequently which ones were almost as good or far away from their 'ideal'. They too discovered that there was no one answer to their question but rather different combinations of parameters that came to the same results.

 

They are completely different approaches and neither one addresses the question of what will be most beautiful to YOU or your beloved. That's because this is an impossible task. Critics of GIA object that it's overly broad and so inclusive as to be meaningless as a selection tool. Critics of AGS object that it's overly specific and that it misses the entire point ... beauty is in the eye of the beholder, not in a computer model. Both sides have valid points and, in the end, it's up to the consumer to decide which one, if either, they want to give more weight.

 

Neil

 

 

I feel AGS should have conducted a study to confirm that people IN THE MAIN prefer the AGS cut grade 0 to AGS cut grade 1 and so on. Pharmacutical manufacturers have to conduct clinical studies to prove their medicines work. They can not just make claims that a medicine works. AGS have to prove in the main that people AGS cut grade 0 diamonds to AGS cut grade 1. They have not done this! That's what I find very disturbing! It's like the cosmetic industry claiming the next greatest cream will banish all wrinkles and leave you looking like you're 21! They don't have to back up there claim with a clinical study, we all know where that has led...

 

Auberry

Edited by AverageJoe
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But GIA has done this type of comparative study and found that the visual nuances between different (external number levels) of Cut Quality can not be neatly quantified or pigeon holed. Visual perception differs between individuals and brilliance, dispersion, and scintillation is perceived differently by different people. preferences are subjective and also critically depend on the lighting environment in which the diamond is viewed in.

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I really don't have to use machines to tell me which stone is pretty and many of my in store clients don't either because they are actually looking at the diamonds and comparing side by side. However many people today buy in the blind online only using a couple of numbers on a piece of paper to tell them how beautiful a diamond is. Then there are other sites online that use a numbers system to put a cut grade on a diamond such as premium, ideal very good etc. All without even seeing a single stone. At least with light performance technology, it isn't us just saying it is a pretty stone. It actually provides proof that the stone has something very special going on when it gets very high readings. Many vendors can say the stone is pretty. Especially when they are selling it, but do they offer any proof that it is a gorgeous diamond?

 

 

In fact this technology can kill a sale just as fast as making a sale. For instance you get a stone that sounds really nice on paper. Then get the stone in, only to find out it's a dud.

 

We have tested the machines with our in store clients and ourselves as well. They pick out the prettiest stone to their eye, and then we put it on the machine. So far 100 times out of a 100 they picked the one with the highest light performance. :)

 

Also have had one of our suppliers send us an AGS 10 cut grade at one time, and this stone was an experiement in cutting. It got one of the highest light performance grades on the machine. The stone was very bright and gorgeous, however not cut to the norm. Had it gone to the AGS lab it would have received a 10 based on numbers only.

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AGS have to prove in the main that people AGS cut grade 0 diamonds to AGS cut grade 1. They have not done this!

Auberry

AGS makes no such claim (although perhaps some of their members do). Even GIA hasn’t made a claim like this. AGS has declared a set of mathematical requirements for a stone to be called ‘0’ whilst ones that are close get ‘1’ etc. There is no discussion at all about what is likely to be popular with most people. There was certainly an attempt, successful in my opinion, to make AGS-0 describe stones that most people would call beautiful but this is NOT one of the requirements for the grade and they make no claim that AGS-10’s can’t also be beautiful.

 

Although the GIA approach is based on popularity, even they don’t make claims about the population in general. The people in their study, at the time of their study, seemed to prefer some specific combinations over others. A different study group or the same group at a different time or with minor changes in things like the sorts of lighting environments used or the size of the stones may very well have come to different conclusions.

 

Neil

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We have tested the machines with our in store clients and ourselves as well. They pick out the prettiest stone to their eye, and then we put it on the machine. So far 100 times out of a 100 they picked the one with the highest light performance.

 

Of course this would NOT include any shoppers looking for a fancy Shaped diamond- or heaven forbid, a fancy colored diamond.

Each of these would bounce back less light that a round- making them...less pretty????

 

Also- couldn't the suggestion, or the way you react when you tell them the results have something to do with it?

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Yes we do light performance on fancy shapes. They are measured against each other in the same shape.

 

As far as colored diamonds, I don't believe they have a cut grade. Also they are cut for color, not light performance.

Edited by jan
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From what I've read,AGS is a performance based system. An AGS stone with out-of-the-ordinary proportions could just as easily be rated an AGS-triple-0 as one with typical proportions. AGS provides some ranges as guidelines to those doing the cutting but the actual cut rating is performance based. Thus, a stone with atypical proportions and fantastic light performance would appear as such on paper: AGS-0 Ideal Cut with unusual proportions.

 

GIA on the other hand is based completely on proportions. Their system might be better, who knows. I'm not saying one system is better than the other; however, in buying a diamond I did choose to stick with AGS because I have information on both the proportions and light rating if I make some effort to understand them both.

 

I don't necessarily agree with this criticism of buying online. Going to a retail outfit you certainly have advantages: instantly compare multiple stones and have an expert guide you through your decision; however, you also have limited inventory and will pay a hefty premium. If you don't want to do any research for yourself that premium is probably worth it assuming you've found yourself a reputable jeweler. Make no mistake though: it's just as easy to be led astray in a jewelry store as it is on the internet. Not all jewelers (less than half of the ones I've dealt with) have shown me the best of intentions. If I felt I was being given a straight story and was getting truly expert advice, I would have dealt with that person over fishing for a diamond on the web any day of the week.

 

It's easy to overpay for a poor quality. That's true in a retail or an online setting. At the end of the day, you've got to educate yourself to make a smart purchase.

Edited by mmath
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From what I've read,AGS is a performance based system. An AGS stone with out-of-the-ordinary proportions could just as easily be rated an AGS-triple-0 as one with typical proportions. AGS provides some ranges as guidelines to those doing the cutting but the actual cut rating is performance based. Thus, a stone with atypical proportions and fantastic light performance would appear as such on paper: AGS-0 Ideal Cut with unusual proportions.

AGS uses the term ‘performance based’ to describe their grading scale but I think it’s slightly deceptive. The term is used to differentiate the current system from the pre-2005 rules that they call 'proportion based'. Like GIA, AGS bases the cut grade strictly on measurements and mathematics where the only human perception that goes into it are the finish grades (polish and symmetry). They do not directly measure the optics of the stone, they measure the angle and azimuth of every facet on the stone and calculate the expected ‘performance’ mathematically using a computer model.

 

I like the AGS system, I prefer it to GIA’s and I’m proud to be a full AGS member and one of their most credentialed titleholders (I have every gemological and appraisal credential they offer and I’m one of only 14 ICGA’s in the world). It does include a variety of combinations that will result in a 0 grade and it’s a significant improvement over the pre-2005 approach where there were only 5 measurements used and each stood on it’s own for what was acceptable but it does not allow any room for surprises. With the current system the angles and measurements are viewed as a collective rather than each standing alone. That said, it does not include a judgment call by the lab grader for stones that they find lovely despite the proportion set being outside of the expected.

 

Neil

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Amazing credentials Neil!!

 

In terms of the "light return" machines- I feel the whole premise is faulty.

If a diamond bounces more light back from a laser, I don;t feel that makes it "better"

For example: if a round diamond bounces back more light in this machine- is it better than an emerald cut diamond?

 

As far as colored diamonds, I don't believe they have a cut grade. Also they are cut for color, not light performance.

Actually Jan, Neither Fancy Shaped OR Fancy Colored diamonds have an established GIA "Cut Grade"

But clearly, if a cutter wants to sell a fancy colored diamond it better be...well, shiny. The best cutters of Fancy Shaped diamonds certainy DO pay attention to the quality of cut.

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Amazing credentials Neil!!

 

In terms of the "light return" machines- I feel the whole premise is faulty.

If a diamond bounces more light back from a laser, I don;t feel that makes it "better"

For example: if a round diamond bounces back more light in this machine- is it better than an emerald cut diamond?

 

As far as colored diamonds, I don't believe they have a cut grade. Also they are cut for color, not light performance.

Actually Jan, Neither Fancy Shaped OR Fancy Colored diamonds have an established GIA "Cut Grade"

But clearly, if a cutter wants to sell a fancy colored diamond it better be...well, shiny. The best cutters of Fancy Shaped diamonds certainy DO pay attention to the quality of cut.

 

 

 

 

 

I agree with you whole-heartedly, otherwise why not fit a laser on to a ring. It would not only be larger and brighter than any diamond, with the added benefit of being able to vaporise any potential thiefs.

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First of all, colored diamonds are really quite rare.There are 10,000 white diamonds for every colored diamond. I"ve been selling them for quite a while and haven't seen the cutters following an ideal set of numbers for color diamonds. In some instances cutting them too good can wash the color intensity out of the diamond. That is why I find sometimes the stones are deeper and definitley not cut to ideal proportions that round diamonds are.

 

But then again, maybe your not familiar with the ideal cut standards.

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It's true Jan, Fancy Colored diamonds are quite rare-but we deal extensively in them. We have a lot of sources for extremely well cut Fancy Colored Diamonds.

True- they are not the same as "ideal" cut rounds- for each one is more unique.

 

Without question, it's a specialized skill ( the cutting of Natural Fancy Rough)- and without question, some cutters get it wrong.

 

In terms of depth, true, many of the deeper colored diamonds also have greater depth- but remember, most of the Fancy Colored Diamonds are NOT Round- Radiant, and Cushion, for example, could be considered well cut with depth ranges into the '70's

 

But there's also some really well cut Vivid Yellow Diamonds with more moderate depths- truly well cut diamonds by any standard.

We've got several Natural Fancy Vivid yellow Radiant Cuts in stock with great cuts- one is 1.20cts with a depth of 63.9- extremely well cut radiant, not deep by any means.

 

They are out there......

 

When you say "Ideal Cut Standards"- are you referring to AGSL standards?

Edited by diamondsbylauren
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