David Atlas advocates a simple direct approach to diamond grading

[pricescope]

New article by David Atlas: Making the case for Imagem diamond grading.

 

[Garry H (Cut Nut)]

reading over coffee

 

[oldminer]

Thanks to those who have gone to the Pricescope Journal for a look. It is a message that I believe will become more widely known and discussed in the months to come.

I''m told that often a small company with a new technology surpasses the offerings of the blue chip firms that have been in control of a market. With large size comes bureaucracy, hesitancy to rock the boat, and once committed to a course a large entity is like a freight filled ship which moves onward, right into the iceberg, no matter how hard the crew try to steer it otherwise.

We are continuing to look for normally cut diamonds which would cast any doubt on the rather simple measures of Light Behavior we suggest. To date, none have been found or offered to us for examination that would put these measures in doubt.

 

[Garry H (Cut Nut)]

Thanks Dave,

I have taken (roughly) some extracts and will add comments and questions in blue.


Making the case for ImaGem grading
When one looks for solutions to problems it is best to look for the simplest possible one.

There can be problems with simplification if the problem is not one to be simplfied. This problem is complex and because we have labs with complexity constraints we end up with a market that is 2/3rds round and princess cuts - that is bad for consumer choice and business creativity and excitement. The biggest issue I have with direct assessment is they can not be used to develop new cuts.

one would always use a scale to obtain the exact weight of a diamond in preference to measuring the length, width, and depth and then using the GIA formula for the particular shape to estimate the weight. We use weight for historic reasons - but today we could just as easily use Volume - or as is the case with many goods - millimeters - eg who would ever buy Swarovski crystals by weight?

...the AGA Cut Class system ….for the best cut round and fancy shaped diamonds …..based on parametric measures of the diamond and grounded in the Tolkowsky-like model that jewelers had grown to accept as the basis for best cut.
Unfortunately the interpretation of Tolkowsky as a single target rather than a sloping range has led to a huge loss of diversification of round diamond appearances that many people would have found very attractive - but it will take another 5 years or so for most of you to understand this because of jewelers had grown to accept as the basis for best cut.

Brilliance: is arrived at by computing the mean gray-scale value of all pixels within the girdle portion of a diamond.
Sparkle:. This measure is arrived at by measuring the standard deviation in the gray-scale value of the light return within the girdle image.
Intensity: a measure of the number and strength of contrasting light-dark areas

Dave you have agreed to contribute to the small Master Stone Study that will be a start to providing some answeres to putting a human scale onto some of these terms. I hope that ImaGem will take the opportunity to gain knowledge from this survey - and perhaps become a major contributor in the future to the additional studies that are required - read on:
The greater the stone''s symmetry the higher its intensity will be. How do we know? This might be true for a .30ct but not true for a 5ct round for example - we do not know of a machine or system that can make these assessments yet with any degree of accuracy.

The next extracts concern ImaGem''s system - but to make a thorough assessment we have many questions - the box is still a black box - yet it is protected by patents just as Brilliancscope is - yet they allow people to check the lighting and angular positions etc.

This measure is arrived at by calculating a ratio of bright pixels to the total number of pixels within the girdle.
our data shows that agreement on color grading among experts is only 65% under the best conditions in proper laboratory environments. This is why labs differ in their grading of color and nothing but an advancement of technology stands to cure the human inability to color grade to a higher degree of consistency.
The brilliance reading is the AVERAGE of all the pixels within the face-up view of the girdle outline, Better diamonds do return more light, but a diamond hat returned enough light o show only white pixels would have no beauty or merit. It would be very bright, but not sparkly or show contrast. The best round diamonds show 200 to 150 gray scale average values. The best princess cuts show 200 to 130 gray scale average values.
Star patterns etc?
What ImaGem does is calculate the brightest range of pixels and reports it as a percentage of the total number of pixels. When you see an ImaGem Intensity grade of 200, all you do is move the decimal 1 space to the left and you have 20% as the percentage reading of the brightest pixels compared to the total. It is a measure of contrast.
The three measures tend to rise as diamonds become higher in light return,
Take contrast for example - there can be many variants on this idea - eg GIA looked at proportion sets that create large enough to see dark zones (but the dark zone in a .30ct diamond might not be visiible because they mainly used bigger stones - but they never used 5ct stones - so the dark ugly zones in large stones mean GIA''s system cant work there. Does ImaGem solve this problem - or would a .3ct and 5ct otherwise identical stone get the same grade?
There are many such examples - too many to ask.


Few, if any, fancy shaped diamonds can outperform or match the Light Behavior scores of round diamonds, yet many people prefer them. Sergey believes better than Tolkowsky round is possible - but we must provide the tools (he must) to make this possible - Imagem and other direct systems could maybe measure this

The Durability measure looks at culet size, crown angle, and girdle thickness. The Finish measure looks to symmetry and polish. Finally the Size measure looks at the relationship of spread, diameter, to depth.
In the spirit of AGS who have openly shared their rules for such matters - could we have them listed for discussion and possible helpful suggestions please Dave?
eg on HCA I have a warning that says a Medium girdle is dangerous at say a 30 degree crown angle - but a Very Thin girdle is OK with a 36 degree crown angle. A thick girdle on a 28 degree crown angle is fine from a durability point of view.

ImaGem’s VeriGem equipment will be available for hands on, private sessions at the upcoming 2006 NAJA Summer conference and at the San Diego 2006 GIA Symposium.
Looking forward to it Dave

Not to mention breaking bread washed down with vino

 

[oldminer]

I can reply in a meaningful way to some of the questions, but not all. Certainly, there are several unknown potentials left in all of this. Logic does not always hold true.

Take contrast for example - there can be many variants on this idea - eg GIA looked at proportion sets that create large enough to see dark zones (but the dark zone in a .30ct diamond might not be visiible because they mainly used bigger stones - but they never used 5ct stones - so the dark ugly zones in large stones mean GIA''s system cant work there. Does ImaGem solve this problem - or would a .3ct and 5ct otherwise identical stone get the same grade?
There are many such examples - too many to ask.

Remember that I said that diamonds are to be cut in the normal way. I am certain we can get higher ranges of performance in larger diamonds by adding properly placed facets. As a lab, I leave the design work to cutters and their predictive devices. Come up with better diamonds, and we are prepared to grade them. ImaGem does not need to solve the problem of how to cut a diamond. It solves the problem of how to grade already cut diamonds. ImaGem will be offering lab services to cutters to improve and recut existing diamonds to higher performance levels. We will garner this information from diamonds that have been examined and it will be factual, not predictive.

There can be problems with simplification if the problem is not one to be simplfied. This problem is complex and because we have labs with complexity constraints we end up with a market that is 2/3rds round and princess cuts - that is bad for consumer choice and business creativity and excitement. The biggest issue I have with direct assessment is they can not be used to develop new cuts.
We think the problem of measuring performance has been solved. It was a bad choice to go down the predicive direction because of the obvious complexity, and inherent innaccuracy. ImaGem is not stuck with only being able to grade two or three shapes. Cutters are really smart and have developed all sorts of pretty diamonds without any predictive tools. They will continue to do this. Laboratories don''t necessarily have to take a lead role in product development. That is another business entirely. Predictive tools will be great help creativity and cutters, but I think the situation we are in today is partially from a false belief in what technology should be doing. You can''t take predictive devices into a lab environment and make them into grading tools. It is, indeed, too complex a problem for them as the trade must begin to see.

one would always use a scale to obtain the exact weight of a diamond in preference to measuring the length, width, and depth and then using the GIA formula for the particular shape to estimate the weight. We use weight for historic reasons - but today we could just as easily use Volume - or as is the case with many goods - millimeters - eg who would ever buy Swarovski crystals by weight?

Of course, we could use volume or millimeters. These are also directly measured amounts. You can''t give me an example of anything we grade via predictive measure where we can directly measure it. Can you? Can anyone find this proverbial needle in a haystack? We use weight with diamonds, but could use milimeters or volume. We would measure those things directly, still. Can you make a case for predicting milimeters or volume and using that instead as a "standard"?

...the AGA Cut Class system ….for the best cut round and fancy shaped diamonds …..based on parametric measures of the diamond and grounded in the Tolkowsky-like model that jewelers had grown to accept as the basis for best cut.
Unfortunately the interpretation of Tolkowsky as a single target rather than a sloping range has led to a huge loss of diversification of round diamond appearances that many people would have found very attractive - but it will take another 5 years or so for most of you to understand this because of jewelers had grown to accept as the basis for best cut.

This may be very true. No reason here to believe otherwise. We will absolutely have more different cuts over the coming years than in the past 100 years. My Tolkowsky belief was based on what I had been taught. I was making a business choice in the AGA Cut Class grades and was waiting for the business to evolve to another level all along.


The Durability measure looks at culet size, crown angle, and girdle thickness. The Finish measure looks to symmetry and polish. Finally the Size measure looks at the relationship of spread, diameter, to depth.
In the spirit of AGS who have openly shared their rules for such matters - could we have them listed for discussion and possible helpful suggestions please Dave?
eg on HCA I have a warning that says a Medium girdle is dangerous at say a 30 degree crown angle - but a Very Thin girdle is OK with a 36 degree crown angle. A thick girdle on a 28 degree crown angle is fine from a durability point of view.

http://www.gemappraisers.com/lbidfs.htm This is an OPEN matter and has been on my website for several months. There has never been any secrecy involved. We always look for meaningful input and fair criticism. Your example of a 28 degree crown angle on a thick girdle makes good sense. We might downgrade the diamond for the thick girdle and/or the shallow crown angle. You can''t defend such a diamond as a finely crafted stone. It may be a great looking diamond, but not among the best cut ones. We lower the grade on DFS for faults of durability, finish and size (spread).

We''ll have some fun in San Diego!!!!!!!!!!!!!

 

[strmrdr]

Interesting Dave.
Thanks to a certain person being a bit of a jerk(yea I admit it) the degree of openness by Imagem has improved over time. Id like to say thanks for opening up on it.

Now not trying to be a jerk I have a question.
First some background.
Anytime I come across a new tool I compare it to the tools im familiar with to get its position on my tool chain and get a handle on what it is telling me.
With that in mind and because the IS and the HCA are the most understood tools on PS would it be possible to get the imagem results compared to IS and HCA results for some diamonds in a future journal article?

 

[oldminer]

I''d be glad to compare results of ImaGem with any tool people are familiar with. Most of the tools we have don''t create discreet readings, but the HCA does. I have supported the use of the IS and the HCA for as long as I have known of them.

If anyone wants to have me run a stone for a test situation, it is no problem. Come prepared to the GIA Symposium with your best examples. We''ll do what we can there or at my Philadelphia lab.

 

[denverappraiser]

David,

Is Imagem now selling equipment to labs or is this service strictly available to US clients from you? Is Philly the only location where this can be done?

Neil Beaty
GG(GIA) ISA NAJA
Professional Appraisals in Denver

 

[oldminer]

ImaGem is in the process of negotiating placement of equipment in a couple of the larger international labs we are all familiar with here. I can't say who at the present. Other users will be coming visible shortly, but again, secrecy of their names has been requested.

We use the ImaGem equipment at AGA in Philadelphia, DGLA a lab I am a partner in outside Philly that does work for major chain retailers, at DGLA in Mumbai, India where we do this work right at the manufacturing facilities of major retailer clients, and in Surat, India where ImaGem opened its own beta-site lab operation.

The VeriGem is for sale, but the revenue model is based on a per stone basis with about a $19K upfront licensing cost. Needless to say, one must have a fairly substantial monthly usage to make it practical for ImaGem to give 24/7 support, and secure data recording facilities. We expect to offer lower cost smaller lab equipment in due course for both lab use and retailer use at the counter. It still may be usage based, but the out of pocket money would be a lot less.

 

[denverappraiser]

David,

Best of luck with your sales efforts! I know that you and Dr. Agarwal have been working on this for years and it sounds like it’s coming together. I certainly understand that the identity of potential clients is a sensitive piece of information. Keep us posted as it develops.

Gemprint as it has existed for the last decade or so has shut down operations and this may leave you an opening in the market for the Verigem service. Is that service currently available from anyone other than your labs?

Neil Beaty
GG(GIA) ISA NAJA
Professional Appraisals in Denver

 

[oldminer]

Gemprint continues to be offered along with GCAL lab reports, but from what I gather, the stand alone Gemprint operation is going or gone. VeriGem is able to do the work of a GemPrint at the same time it does the Light Behavior grading. We offer "Registration", basically the equivalent of a Gemprint right now. I think the fees for the public are on the ImaGem website. I feel pretty certain all our retail counter, small and large lab devices will provide a Gemprint-like capability. (faster and for a somewhat lower cost, too)

Behind the scenes of the devices ImaGem is producing, is a highly integrated Laboratory Information System software package which may be tailored to fit large lab operations where efficiency and throughput are crucial. Just think how many times during a diamond grading job you pick up the diamond, pick up the loupe, take another look in the microscope, pick up the pen for plotting, look again, plot more, measure once, then again, etc, etc. This lab system makes each operation a one time only affair. It makes a record at the end of the job and creates invoicing without further entry work if you want it to. These fellows know the throughput capability of each component workstation in a lab system. Knowing this means you can project how much equipment of each type and how many people are needed to operate it during the hours you choose to be open. When we recently graded many thousands of diamonds in a relatively short time frame, a projection of our capabilities and where we'd have bottlenecks was crucial in deploying sufficient equipment and people to get the job done on time. I have never seen anything like this in the jewelery business before. It was quite an eye opener for me to see how the technology and programming long used in big business has now begun to migrate into our own field.

 

[denverappraiser]

GCAL purchased Gemprint Corp. and is using some of the technology as part of some of their services but clients who don’t live in NYC, or who don’t want to ship their valuable property to NYC, have no way of either getting a stone scanned or of matching a stone to a previous scanning to see if it’s the same. The service that was offered by Gemprint Corp. is no longer available to 99% of the customers who might otherwise be interested in it. GCAL may put together some sort of program in the future to make an identification and matching service available but, so far, I’ve seen no indication that this is in the works. In the meantime, there is no service available and the value of the Gemprint brand for this sort of thing is evaporating through disuse. Their plans seem to be other services entirely. We’ll see what evolves with them. Their loss may be your gain. If yours has additional functionality, that’s even better. I can’t say I want to prepay for $19k but when you get the pricing structure worked out, give me a call. I may be interested.

Neil Beaty
GG(GIA) ISA NAJA
Professional Appraisals in Denver

 

[Garry H (Cut Nut)]

Thanks for your responses above Dave.
Only one remaining issue:

Date: 7/7/2006 8:48:27 AM
Author: oldminer

http://www.gemappraisers.com/lbidfs.htm This is an OPEN matter and has been on my website for several months. There has never been any secrecy involved. We always look for meaningful input and fair criticism. Your example of a 28 degree crown angle on a thick girdle makes good sense. We might downgrade the diamond for the thick girdle and/or the shallow crown angle. You can''t defend such a diamond as a finely crafted stone. It may be a great looking diamond, but not among the best cut ones. We lower the grade on DFS for faults of durability, finish and size (spread).

We''ll have some fun in San Diego!!!!!!!!!!!!! We will

Dave the attached Gem Adviser File has a thick GIA girdle and 28 crown. This would be a highly desirable stone if shown to anyone who did not know its proportions. It has a 28 degree crown angle, 55% table and 60.3% total depth (pavilion angle is 41.55). It would be very difficult to chip this girdle as I am sure you would agree. (If you dug the upper girdle facets a little you could even improve this stone further).
This stone has a spread that is 2.5% better than Tolkowsky.

Thanks for pointing me to your standards.
I would be happier to see you using the approach we developed for DiamCalc that AGS subsequently used - one that relates spread to Tolkowsky or some such standard.

For example it is possible to make a diamond that has 63% depth and at 6.48mm (a nice 1ct size) the stone would weigh in at 1.17ct.

 

[oldminer]

Those examples of round cut that contradict the DFS and AGA Cut Class ranges are indeed interesting exceptions to the norms. There are always strange exceptions, but one would wish to include them if they truly qualify. I wonder if rough comes in a way that any cutter would ever cut such stones? I don''t think I have ever seen any cut that way and cutters are very creative. Predictive tools may give you a suggestion that cutting in such a manner would be pretty, but we are interested in the 98 or 99 percent of diamonds that can be graded with standard tools in an efficient manner, not a couple weird exceptions that would always need the input of a chief gemologist in a lab. Whenever we create standards there will be a small percentage of exceptions, but we should not refuse technology because it can do certain limited tasks when it can do nearly everything else better.

Dr. Aggarwal uses the analogy of the early 1900''s when folks said cars are a novelty. They said, """What will you do when you come to a fence?" "Only a horse can jump over a fence." Well, cars still can''t jump over fences, but you see where the horse is today. All they do is jump fences. When it comes to transportation, cars have done a superb job.

The other thing about diamonds that might be cut in unexpected ways. They may look very nice and receive a rather high performance grade, yet be downgraded for their cut by the DFS. We report these results as separate grade, so there is no negative result in the "pretty" aspect of performance. People do tend to follow the herd when it comes to what they choose. Giving a lower DFS grade would announce that the stone has a problem. The problem on such a diamond is its strange configuration. I would bet a dollar or two that such a diamond would sell for a large discount from a regular cut even with a great spread. It would be hit hard in liquidation, too. People looking to buy a non-controversial stone would avoid such a strange one.

It might even be called a disservice to give such a diamond a high overall grade since most dealers would find such a cut objectionable. Maybe, in time, they would overcome their years of experience and prejudice, but I don''t believe it would be anytime soon. My way of thinking suggests that your example highlights a striking weakness in predictive tools which fail to address the standard appearance people expect when they blindly agree to buy a diamond from an expert. All the real facts are in the hands of the experts. If the paperwork the consumer gets fails to report that a particular diamond is cut in some unusual manner which will have an adverse effect on its saleability and value, then somehow the consumer is being duped.

The DFS subtly addresses the issue of standard cutting in a quiet and consistent manner. No one is left in doubt. Performance is reported as one grade and DFS is reported in another. The customer may choose what they consider beautiful with sufficient knowledge of the market facts. Those who are the lookout for beauty alone and don''t care about configuration may well choose a spready, thick girdle diamond. These may be a great stone for earrings or a pendant if anyone ever cuts a pair.

 

[Garry H (Cut Nut)]

Wow Dave - we are getting somewhere!

Because the trade got fixated on a single target (tolk) anything too far from it was considered bad.

Rough has a number of ways it would like to be cut.

Octahedral ( http://images.google.com/images?svnum=10&hl=en&rls=IBMA,IBMA:2006-14,IBMA:en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=octahedral+diamond&spell=1 pyramid on a pyramid) Sawn just above the center will be the usual most economic way. In this case near Tolkowsky with a slightly deeper pavilion is a good solution.

But the sawn top is screaming to be cut with a +60% table,

But the Gem Adviser stone I posted above yeilds better than a Tolkowsky stone from this sawn top - or indeed any other flat piece of rough like a maccle or flat. maccle This is a BIC type stone - less fire but heaps of brightness.

With smaller octaheda - ones that would normally yeild a 6-6.4mm 1ct diameter stone, a better yeild can be obtained by cutting a steeper crown angle, and shallower pavilion with a tiny table - near 50% or under. An old cut (which I know you like) would also usually have a deep pavilion - but I know you have also so seen stones like this that had shallow pavilions - because they were cut from the other common type of rough - Dodecahedra or makeable - called a makeable because it does not need to be sawn / cleaved to produce 2 or more stones or any thing other than made into one single diamond.

This is a FIC - Firey Ideal cut

But because the market pulls cutters back to Tolkwsky we simply never (rarely) see these stones becauese they are penalized in the market.

They are beautiful. They produce a better yeild.
They may not produce as good a yeild as the crap that generally gets produced from these roughs - but that is such a shame because if the trade had not adopted "Tolkowsky-like model that jewelers had grown to accept as the basis for best cut"

then we could have had natural common sense that anyone can see by looking at the HCA charts here - the slope of nature that says that there is a 4:1 or 5:1 inverse crown / pavilion angle to create the best looking stones.

Bruce Harding discovered it, I discovered it with the ideal-scope, MSU discovered it, GIA and AGS discovered it. Many old cutters - pre lab grading and reporting knew and practiced it.
This is a natural law because the law describes what happens in nature.

Physics is the science of Nature in the broadest sense. www.wikipedia.org/wiki/Physics


So we have probably wasted and reduced the value and beauty of hundreds of billions of dollars worth of diamonds over the past near century and Tolkowsky and Morse would be the prime causes of this.


I am looking forward with some excitement to being part of the solution to arresting this huge wasteage. I hope many of you will come along for the ride. Sergey is the navigator and the engine. Leonid has helped by laying some tarmac. Many others have contributed because they can feel the energy and know instinctively that this will be a worthwhile journey.

 

[Garry H (Cut Nut)]

and Dave there will be a need for other methods to show that the beauty of the diamonds that come from these developmenets are indeed beautiful.

I forgot to post this chart

 

[oldminer]

It would be easy enough to alter the way DFS grades diamonds. If the market agrees that these presently strange diamonds are desirable, then I have no personal problem with making changes toward that direction. We are fixated on Tolkowsky being the center of our present universe. You and a few others are the exceptions and you may find market acceptance at some point. I'm flexible as I see many diamonds that look excellent that are not exactly traditional ideal cuts.

Standards are tools we use to structure or expalin the market. If the market changes, the standards may need to be adjusted. As always, I look to learn about these things. Knowing more is far superior to being in the dark. THANKS

 

[Garry H (Cut Nut)]

it is worth thinking about Dave - extra work - but it is how i would do it. Date: 7/8/2006 7:36:30 AM
Author: oldminer
It would be easy enough to alter the way DFS grades diamonds. it is worth thinking about Dave - extra work - but it is how i would do it. If the market agrees that these presently strange diamonds are desirable, then I have no personal problem with making changes toward that direction. We are fixated on Tolkowsky being the center of our present universe. You and a few others are the exceptions and you may find market acceptance at some point. I''m flexible as I see many diamonds that look excellent that are not exactly traditional ideal cuts.


Standards are tools we use to structure or expalin the market. If the market changes, the standards may need to be adjusted. As always, I look to learn about these things. Knowing more is far superior to being in the dark. THANKS

thanks for reading Dave

 

[He Scores]

Date: 7/7/2006 9:27:15 PM
Author: Garry H (Cut Nut)
Thanks for your responses above Dave.
Only one remaining issue:

Date: 7/7/2006 8:48:27 AM
Author: oldminer


http://www.gemappraisers.com/lbidfs.htm This is an OPEN matter and has been on my website for several months. There has never been any secrecy involved. We always look for meaningful input and fair criticism. Your example of a 28 degree crown angle on a thick girdle makes good sense. We might downgrade the diamond for the thick girdle and/or the shallow crown angle. You can''t defend such a diamond as a finely crafted stone. It may be a great looking diamond, but not among the best cut ones. We lower the grade on DFS for faults of durability, finish and size (spread).

We''ll have some fun in San Diego!!!!!!!!!!!!! We will

Dave the attached Gem Adviser File has a thick GIA girdle and 28 crown. This would be a highly desirable stone if shown to anyone who did not know its proportions. It has a 28 degree crown angle, 55% table and 60.3% total depth (pavilion angle is 41.55). It would be very difficult to chip this girdle as I am sure you would agree. (If you dug the upper girdle facets a little you could even improve this stone further).
This stone has a spread that is 2.5% better than Tolkowsky.

Thanks for pointing me to your standards.
I would be happier to see you using the approach we developed for DiamCalc that AGS subsequently used - one that relates spread to Tolkowsky or some such standard.

For example it is possible to make a diamond that has 63% depth and at 6.48mm (a nice 1ct size) the stone would weigh in at 1.17ct.

You gentlemen will pardon this Tolkowsky lover here for a moment won''t you?

Once again, I would like to say that diamonds are pieces of sculpture and not to be viewed ONLY in one position. Any system relying on this one particular view IMHO is weaker than Tolkowsky''s math or thin girdle on his model. You must remember that when Tolkowsky wrote about his model, the trade corroborated his findings by offering up their version of what they accepted to be high standards.

You don''t find this consensus today among the trade when it comes to these performing stones. Why? In short, because static face up view is not a worthwhile platform. Take the above stone for an example. First off, let''s just ASSUME that all the angles are 28 degrees. Which anyone knows they aren''t, won''t be, etc. but let''s say they are. This may or may not look good in the face up, but it would have such a lack of definition between all the facets on the crown that the stone would just "lay" there when looked at it from other angles.

To say that it would be a highly desirebable stone "if someone didn''t know the proportions" doesn''t seem applicable except to say that a lay person would say that stone is nice. That should not be the basis for any sort of standard, which by the way is what we should be striving for in the trade.

My reading of the pulse of the industry is that the trade does not want "broader" ranges for what is an excellent stone. This is tantamount to giving "softer" grades on color and clarity. You may think one would benefit by getting a better color (or read cut or clarity) on a report than the stone actually is, but that''s not the case. It leads to non-sales, returns of memo etc. Why? Because eventually someone who knows stones won''t accept it.

The trade wants, and is demanding, and eventually will get strict standards. You may poo poo Tolkowsky and his angles (which basically is all he gave us....the rest is simple basic math), but what he gave us is not sloppy. The Tolkowsky model is a model that is virtually unattainable to the the poor cutter at the wheel. The Tolkowsky model looks good from all viewing positions.

The face up look with the neked eye is not how this trade judges cut. I''ve done my own research on it. The face up look is just that. A face up look. Far too broad to ever be accepted as a standard for look, let alone cut.


Bill Bray
Diamond Cutter

 

[Garry H (Cut Nut)]

Date: 7/8/2006 9:06:53 AM
Author: He Scores


You gentlemen will pardon this Tolkowsky lover here for a moment won''t you?

Once again, I would like to say that diamonds are pieces of sculpture and not to be viewed ONLY in one position. Any system relying on this one particular view IMHO is weaker than Tolkowsky''s math or thin girdle on his model. You must remember that when Tolkowsky wrote about his model, the trade corroborated his findings by offering up their version of what they accepted to be high standards.

You don''t find this consensus today among the trade when it comes to these performing stones. Why? In short, because static face up view is not a worthwhile platform. Take the above stone for an example. First off, let''s just ASSUME that all the angles are 28 degrees. Which anyone knows they aren''t, won''t be, etc. but let''s say they are. This may or may not look good in the face up, but it would have such a lack of definition between all the facets on the crown that the stone would just ''lay'' there when looked at it from other angles.

To say that it would be a highly desirebable stone ''if someone didn''t know the proportions'' doesn''t seem applicable except to say that a lay person would say that stone is nice. That should not be the basis for any sort of standard, which by the way is what we should be striving for in the trade.

My reading of the pulse of the industry is that the trade does not want ''broader'' ranges for what is an excellent stone. This is tantamount to giving ''softer'' grades on color and clarity. You may think one would benefit by getting a better color (or read cut or clarity) on a report than the stone actually is, but that''s not the case. It leads to non-sales, returns of memo etc. Why? Because eventually someone who knows stones won''t accept it.

The trade wants, and is demanding, and eventually will get strict standards. You may poo poo Tolkowsky and his angles (which basically is all he gave us....the rest is simple basic math), but what he gave us is not sloppy. The Tolkowsky model is a model that is virtually unattainable to the the poor cutter at the wheel. The Tolkowsky model looks good from all viewing positions.

The face up look with the neked eye is not how this trade judges cut. I''ve done my own research on it. The face up look is just that. A face up look. Far too broad to ever be accepted as a standard for look, let alone cut.


Bill Bray
Diamond Cutter

Firstly Bill, look at the black line in the chart above - Tolkowsky would have approved of all those proportion combinations. He used his formulas based on one starting point - one mid way thru the range.
Jasper Paulsen and Bruce Harding have independantly reworked Tolkowsky''s math and found multiple proportion combinations that coincide with the laws of nature.
What the trade wants iand what they did with Tolkowsky''s book was the travesty - not what Tolkowsky did.

You should expolre Jaspers site Bill.
http://folds.net/diamond/

Re the 28 crown stone - it is near or maybe over the limits, but I ran tests on that stone thru 30 degrees of tilt with DiamCalc for contrast and light return. It scores Vg and Excellent compared to Tolkowsky. It is rare to see such stones because they often are poorly finished - but that IS my point.

Some years back some detractors to HCA published info on a stone that they said proved numbers do not work. The stone had about a 25 degree crown angle and an accompanying deeper pavilion angle. They were blown away with it. It just happened to fit in a straight line with HCA had I extended past 28 degrees. (if anyone has a link to that thread i would love to find it again).

 

[oldminer]

Bill:

If anyone ever shows any of us a diamond that is not doing the best job face-up which could be defended as a "best cut" diamond, then I will eat my hat. (motorcycle helmet) I agree strongly with your concepts of a diamond as sculpture and that it seems that the general public and the trade appreciate the wide angles that beauty is visible in near Tolkowsky makes. I think you are right in that predicted, extreme examples of shallow crown, no matter how compensated with other features will not look as well in the overall, multi-view positions. We need standards that address the 98 or 99 percent of diamonds and can leave the oddities up to those who look for something different or unusual. A standard, such as proposed by ImaGem, addresses the face-up view as the CRITICAL view which MUST be met with high performance. The DFS lets consumers inside on some of the critical details of cut without ruining the game of salesmanship. Combining Light Behavior and some variation of DFS into only one reported grade seems a disservice to the trade and, more importantly, to the consumer. A score like the BrayScore reported along with an ImaGem grade would be an excellent set of descriptive standards. Much too detailed possibly, but excellent in terms of description.

Consumers want freedom of choice. The market needs different types of cuts with varying values. Creative cutters need the freedom to work on new designs, which you and I may have our doubts about at the present time. As I said, it will take many years for any acceptance to come of unusual and unexpected combinations. Standards reflect the current market. We can always adjust to the reality of a changed market should it occur. Throwing out "exceptions" as a way of saying, "You are wrong." is something toi be examined in a reasonable atmosphere among experts. If the exceptions are truly common and valid then there is a problem, but if the exceptions are quite rare, unusual, worst case scenarios, or pipe dreams, then we can just say that we have solved the problem to a useful extent and we will address the strange exceptions when and if they become more common, problematic or solvable.

Technology solves problems by attacking the vast majority components of a necessary task, not eliminating every and all exception. In time, the exceptions are reduced by improvements in the technology and then they become even less of a problem. The predictive model poses problems that hypothetically exist, and it does not pay to solve theoretical problems with millions of dollars of R&D. One uses money to solve real problems and work toward bettering the technology over time with the revenue stream it creates. That's where I'm coming from....

Thanks for the input.

 

[Garry H (Cut Nut)]

Date: 7/8/2006 12:23:50 PM
Author: oldminer
If the exceptions are truly common and valid then there is a problem, but if the exceptions are quite rare, unusual, worst case scenarios, or pipe dreams, then we can just say that we have solved the problem to a useful extent and we will address the strange exceptions when and if they become more common, problematic or solvable.

The exceptions will never be common because of the choice that tolkowsky made.

He could just as easily chosen 33 degrees as the crown angle to ''try'' and he would have then set that as the basis of his crown angle in the book that would have become the equivalent of 34.5 degrees.

Had he done that then the ideal pavilion angle would have been 41.1 degrees Dave.

Then we would have said that 35 or 36 was too steep and 30 would have been OK (with a slt thk girdle).

Chance has played a major role here.

I suggest everyone who has not spent 1/2 and hour on Jaspers site (link above) should do so.

 

[oldminer]

"The exceptions will never be common because of the choice that Tolkowsky made"


That being the case, then technology will be able to handle the problem even more easily. Those very unusual cuts which somehow get a deducton from the DFS must be carefully looked at by someone like Garry or Jasper who declare them to be superb. This is a function of a highly skilled, chief gemologist in a grading lab: A person with the discretion to overrule a device and a standard, when unusual circumstances dictate. Garry, you don''t need another job, do you?

 

[Garry H (Cut Nut)]

Dave I do not coubt that any well functioning direct assessment instrument willbe able to verify that these unusual stones do look good.

RE the parameters for crown angle / girdle thickness / durability - we can thrash that out with other appraisers here based on our collective experiance.

 

[JulieN]

Date: 7/8/2006 9:44:28 AM
Author: Garry H (Cut Nut)
Re the 28 crown stone - it is near or maybe over the limits, but I ran tests on that stone thru 30 degrees of tilt with DiamCalc for contrast and light return. It scores Vg and Excellent compared to Tolkowsky. It is rare to see such stones because they often are poorly finished - but that IS my point.

Some years back some detractors to HCA published info on a stone that they said proved numbers do not work. The stone had about a 25 degree crown angle and an accompanying deeper pavilion angle. They were blown away with it. It just happened to fit in a straight line with HCA had I extended past 28 degrees. (if anyone has a link to that thread i would love to find it again).

Have only this: http://www.diamondtalk.com/forums/showthread.php?t=54913

 

[Garry H (Cut Nut)]

Date: 7/9/2006 7:04:57 AM
Author: JulieN
Have only this: http://www.diamondtalk.com/forums/showthread.php?t=54913

Thank you thank you, for finding this gem for me JulieN

Dave (and others) do you see that it is possible for diamonds to look good so long as the crown and pavilion angles are withing the laws of nature for peak performance?

(Dave this would be a durability issue as the stone has a thin to medium girdle. I would want such a stone to be at least on the thick end of Slightly Thick, unless a customer wanted to use it for a pendant or ear rings).

 

[oldminer]

I see a diamond with a 25 or 28 degree crown angle as not having such good light performance off the face-up view as a more accepted cut diamond. I could be totally wrong here, but shallow crown diamonds tend to look good face-up and lose more of their good looks within a narrow tilt versus a more standard crown height diamond.

The DFS hits thin and thick girdles with deductions. If a diamond has a "Durability" issue then it takes a discount in DFS. It might be a superb looking stone with a cutting fault. If it has a very thick girdle, then it becomes an issue of girdle thickness, versus better spread. It takes a "Size" deduction. None of this means the diamond might not make a pretty stone worthy of consideration at a "price" that was suitable, but it will take years to convince this traditional trade that such a stone is a premium cut worth the same as the already current large crop of super cut types. Cutters may learn to cut prettier, less costly diamonds and make better use of their precious rough material. This would be of benefit to the trade and the consumer. I believe the ImaGem grader will show these fine performing diamonds do exist if anyone gives us a physical example. I don't doubt the predictive accuracy of Sergey and Jasper's work. Maybe you have a few of these in your store since you seek out those diamonds which work with the Ideal-Scope regardless of how they are cut. I'd love to own a few of these examples for future R&D and for the simple knowledge itself.

 

[Garry H (Cut Nut)]

Date: 7/9/2006 6:46:56 PM
Author: oldminer
I see a diamond with a 25 or 28 degree crown angle as not having such good light performance off the face-up view as a more accepted cut diamond. I could be totally wrong here, but shallow crown diamonds tend to look good face-up and lose more of their good looks within a narrow tilt versus a more standard crown height diamond.
Across 30 degrees of rotation / tilting this stone has 15% less contrast than Tolkowsky, but 21% better light return face up and 6% better thru rotation.
this is anything but an ugly stone Dave

The DFS hits thin and thick girdles with deductions. If a diamond has a ''Durability'' issue then it takes a discount in DFS. It might be a superb looking stone with a cutting fault. If it has a very thick girdle, then it becomes an issue of girdle thickness, versus better spread. It takes a ''Size'' deduction. as is this stone has too thin a girdle - but if it were polished with 4.5% at the mains (Thick) then its 0% better than Tolkowsky spread would have dropped to 4% better than Tokowsky - so spread is not going to Ding it Dave, and it would be hard to break at 4.5% I am sure you would agree? None of this means the diamond might not make a pretty stone worthy of consideration at a ''price'' that was suitable, but it will take years to convince this traditional trade that such a stone is a premium cut worth the same as the already current large crop of super cut types. Not if they were buying and selling with Imagem optical results? Cutters may learn to cut prettier, less costly diamonds and make better use of their precious rough material. This would be of benefit to the trade and the consumer. I believe the ImaGem grader will show these fine performing diamonds do exist if anyone gives us a physical example. I don''t doubt the predictive accuracy of Sergey and Jasper''s work. Maybe you have a few of these in your store since you seek out those diamonds which work with the Ideal-Scope regardless of how they are cut. I''d love to own a few of these examples for future R&D and for the simple knowledge itself.

Cutting these stones is not on the small Master stone Study for the stones we have currently begun to cut Dave - but why dont you ask some of your participating manufacturers in India to do a few?

 

[Garry H (Cut Nut)]

Dave today it loks like as a trade - up we will be buying a .34ct L VS with a 30.6 crown, very good symmetry and very good proportions.
It is not as shallow as the stones we are discussing - and the lower grdles are a bit long - so contrast is down - but does it interest you?

 

[oldminer]

I really want the unusual ones, especially if they will score very high in performance. I feel there should be few of them and we will see what the DFS does to them. The one you are getting sounds much more within the range of spready, shallow top stones which we all see around. If such a diamond belongs in our cut study, then we have a budget for them I suppose.