All AGS 000 and GIA "Excellent" are not created equal

[oldminer]

We have had the opportunity to see quite a few GIA Excellent and AGS 000 cuts and have found a fairly broad range of light performance quality differences within these "top of the market" stones. We have seen AGS 0 princess cuts which scored Excellent+ down to Good on the ImaGem device.

All of these diamonds are very beautiful and possibly the lowest scoring one might please someone best as individual tastes differ. However, we feel that there is a large body of consumers hunting the market for the highest performance stones and that they are willing to pay a premium for a truly top performer. This does not diminish any stone within the top range, but only enhances the value of those near or at the very top of light performance.

Sightholders today don''t feel this premium market is worth their time because they say "no one has asked us for it, and until they do, we won''t look into it." My thought is that informed consumers can drive the market and increase the availability of the most well cut diamonds just by asking for them. The diamond market is extremely sensitive to demand. Diamond cutters have been told by DeBeers to make the most out of the rough material and to promote it, not just cut and wait.

If consumers want the best performing diamonds, there is technology out here today to identify it. Just make your voices heard. The discrimination of placement within the upper grades of GIA and AGS is a relatively easy task for technology. This does not mean that a lesser performing diamond might not make you totally pleased, but for performance nuts, only the most and best is right.

 

[kenny]

Personally I only buy AGS 0 stones (the ones that also are in the GIA EX bullseye).

I tell everyone I know about this too.

I am already thinking about the AGS 0 Asscher I will buy when AGS releases their Asscher cut grades.

I suspect there are many customers like me out there who depend on AGS's 0 cut grade to filter out all but the best cuts instead of learning tons and tons of technical stuff.

I have high standards, and money, but I'm lazy.

God Bless AGS.

 

[Regular Guy]

Date: 8/16/2006 2:24:14 PM
Author: kenny
Personally I only buy AGS 0 stones (the ones that also are in the GIA EX bullseye).

I tell everyone I know about this too.

I am already thinking about the AGS 0 Asscher I will buy when AGS releases their Asscher cut grades.

I suspect there are many customers like me out there who depend on AGS''s 0 cut grade to filter out all but the best cuts instead of learning tons and tons of technical stuff.

I have high standards, and money, but I''m lazy.

God Bless AGS.

Kenny,

You are not taking Oldminer''s bait. He motivated your comment, but you did not respond to it. He says: "We have seen AGS 0 princess cuts which scored Excellent+ down to Good on the ImaGem device." So, Dave says you will not really be protected as well as you''d like, at least in the case of princesses, if you just go with AGS.

Dave''s input is valued on this.

Does he say the same for rounds?

 

[belle]

Date: 8/16/2006 2:36:05 PM
Author: Regular Guy

Date: 8/16/2006 2:24:14 PM
Author: kenny
Personally I only buy AGS 0 stones (the ones that also are in the GIA EX bullseye).

I tell everyone I know about this too.

I am already thinking about the AGS 0 Asscher I will buy when AGS releases their Asscher cut grades.

I suspect there are many customers like me out there who depend on AGS's 0 cut grade to filter out all but the best cuts instead of learning tons and tons of technical stuff.

I have high standards, and money, but I'm lazy.

God Bless AGS.

Kenny,

You are not taking Oldminer's bait. He motivated your comment, but you did not respond to it. He says: 'We have seen AGS 0 princess cuts which scored Excellent+ down to Good on the ImaGem device.' So, Dave says you will not really be protected as well as you'd like, at least in the case of princesses, if you just go with AGS.

Dave's input is valued on this.

Does he say the same for rounds?

right. perhaps we need imagem to confirm our ags pick.

anyway...i do agree that the increase in awareness will increase the demand for top cuts. hopefully cutters will see the demand and subsequently start increasing production. in the meantime, some cutters may have a heyday turning out carat saving steep deeps that can be called 'excellent' (hey! excellent is the best, right!?) diamonds to meet the needs of the consumer that wants the paper that says it's good AND the savings in material for the cutters.

hmph.

hey dave, have you found any gia 'ex's that don't perform well on imagem?

 

[Regular Guy]

Date: 8/16/2006 2:40:43 PM
Author: belle
right. perhaps we need imagem to confirm our ags pick.

Others will hopefully beat me to it, but he would not be the first to criticize the warrantee on light performance for AGS0 Princesses.

I think this is more than reasonable. And...if we will seek an appraiser for more than a document we can give to an insurer, I personally value any appraiser making a measured, supported, case for their business.

 

[oldminer]

We know the situation withprincess cuts for sure. Because round diamonds are a far more standard item, we have not seen so great a range as five levels, but I suspect there will be at least 3 and likely 4 levels of discrimination on AGS 0 rounds. More levels on GIA Excellent.

 

[aljdewey]

Date: 8/16/2006 2:48:26 PM
Author: Regular Guy

Others will hopefully beat me to it, but he would not be the first to criticize the warrantee on light performance for AGS0 Princesses.

I''ve never thought anyone considered AGS0 a "warranty" for anything.

In fact, it''s been said many times during my tenure on PS that reliance on numbers alone isn''t prudent because it''s possible for an AGS0 to be a dud (uncommon, but possible and examples have been posted in the past).

For me, AGS0 grading report acts somewhat like the HCA. It''s helpful in narrowing the pool of candidates, and it increases the possibility of a great find, but the ultimate decider is one''s eyes.

 

[Regular Guy]

Date: 8/16/2006 10:23:09 PM
Author: aljdewey

Date: 8/16/2006 2:48:26 PM
Author: Regular Guy

Others will hopefully beat me to it, but he would not be the first to criticize the warrantee on light performance for AGS0 Princesses.

I''ve never thought anyone considered AGS0 a ''warranty'' for anything.

In fact, it''s been said many times during my tenure on PS that reliance on numbers alone isn''t prudent because it''s possible for an AGS0 to be a dud (uncommon, but possible and examples have been posted in the past).

For me, AGS0 grading report acts somewhat like the HCA. It''s helpful in narrowing the pool of candidates, and it increases the possibility of a great find, but the ultimate decider is one''s eyes.

Possibly we agree more than disagree, Al. Your point is specifically that the buyer''s eyes should decide.

The point, I suppose, with AGS0, is that with it, you''re not relying on "numbers" at all, but rather, probably several expert''s eyes specifically looking at that diamond, with at least a concern specifically about light performance, and evaluating that specific parameter. That being the case, possibly, one could say an appraiser is at best a second opinion, which is Belle''s point.

If one wants to look at the veracity of the first opinion (AGS''s basis for AGS0 for light performance), the suspicion is that their system is relatively open, and pretty well specified for those that know how to read such things. In the alternative, taking a second swing at evaluating light performance, as a system like Imagem would do, if it comes up with a different evaluation...it''s not as clear the basis for the result, as it appears to be less of an open system.

To be conservative, it''s easy enough to spend more money and go with a choice that all opinions agree is tops. But, it can be expensive to be conservative. Hopefully, over time, alternate opinions can be proof checked well enough for their value to prove out.

 

[Garry H (Cut Nut)]

Dave have you eyeballed the princess cuts and can you easily decide that the AGS 0 ''s that rate "good" on Imagem really are easy to pick out from the better stones?

5 grades should be pretty easy for even a GIA clerk to pick?

 

[oldminer]

I did not personally see these princess cuts with the wide range. So far, I think we can visually distinguish a 2 grade separation by eye, but it takes some practice and it remain a subjective opinion without a measuring machine. For sure, the stone that was AGS 0 with an ImaGem "good" light behavior score would look visually different to anyone than another AGS 0 that scored Excellent with ImaGem. That captured beauty shot images are quite revealing and should be part of my powerpoint presentation that will be along with me in San Diego.

 

[Serg]

re:We have seen AGS 0 princess cuts which scored Excellent+ down to Good on the ImaGem device.

Dave, Please publish any real information about such Princess.

For example

1) AGS Report
2) 3D model( Sarin or Helium)

BTW.
1)What is "Good" on the Imagem device?
2) Measurement accuracy choices???? A poll
Do you have plane to publish explanations?

 

[oldminer]

Serg: We have an NDA on those stones, but surely you would be seeing similar things if Helium is on the job. You, in fact, may have more data than I do and certainly have more more than I can release at this time.

The definitions of the overall grading terms are based on fixed combinations of Brilliancy, Sparkle and Intensity measures. The method for this overall cut grade is in a chart on:

http://www.gemappraisers.com/lbidfs.htm

 

[Cehrabehra]

Date: 8/16/2006 2:03:20 PM
Author:oldminer
We have had the opportunity to see quite a few GIA Excellent and AGS 000 cuts and have found a fairly broad range of light performance quality differences within these ''top of the market'' stones. We have seen AGS 0 princess cuts which scored Excellent+ down to Good on the ImaGem device.

All of these diamonds are very beautiful and possibly the lowest scoring one might please someone best as individual tastes differ. However, we feel that there is a large body of consumers hunting the market for the highest performance stones and that they are willing to pay a premium for a truly top performer. This does not diminish any stone within the top range, but only enhances the value of those near or at the very top of light performance.

Sightholders today don''t feel this premium market is worth their time because they say ''no one has asked us for it, and until they do, we won''t look into it.'' My thought is that informed consumers can drive the market and increase the availability of the most well cut diamonds just by asking for them. The diamond market is extremely sensitive to demand. Diamond cutters have been told by DeBeers to make the most out of the rough material and to promote it, not just cut and wait.

If consumers want the best performing diamonds, there is technology out here today to identify it. Just make your voices heard. The discrimination of placement within the upper grades of GIA and AGS is a relatively easy task for technology. This does not mean that a lesser performing diamond might not make you totally pleased, but for performance nuts, only the most and best is right.

I''m not sure I follow 100% with the idea that top-only rated light performance should be the end all of value. Stones viewed at angles often give what is in my opinion a better response. Sure, if what you''re looking for is strictly top-up *brilliance* then all of these tools will accurately judge that... but realistically even when looking at a diamond face up on a finger, how static is that view? Not very. I''m not saying the tools are not useful, I find them particularly useful for judging symmetry... but I don''t think expecting light return to only go in one direction and cutting diamonds exclusively tailored toward that goal is the ONLY way to have a high performing diamond. JMHO.

 

[RockDoc]

Dave

The IMAGEM measures proportions, grades clarity and measures light return performance. What and how does it measure them?

Are you inferring that it is as accurate or more accurate than OGI/ Sarin or Helium.

I keep reading your posts about IMAGEM, and with all that you''re claiming it does, guess no one will need to get gemology education, as it appears that IMAGEM will just about perform any tests conceivable about diamonds.

It appears your claiming the IMAGEM is able to do more in separating ranges of the best, better than GIA and AGS has.
From your comments, seems like its a " little gemologist in a box". I see scales of measurement on your site, but no really discerable transparancy of how this is done and interpreted such as Gemex, GIA and AGS has done. The is no stated amount of variance or tolerance, or a statement that would indicate a percentage of how sure the results are.

200 Light Return Score is indicitive of the "best" or excelllent + . What does the 200 score represent? At the other end of the scale,I see a 0 score. Does that mean NO LIGHT RETURN FROM THE STONE, as that is what it seems to indicate?
I''ve seen some pretty poorly performing diamonds, but in those that are colorless ( rather than black ones or opaque type bort) they all seem to return some light, rather than none.

Where''s the beef?

Rockdoc

 

[oldminer]

Quote:.....but I don't think expecting light return to only go in one direction and cutting diamonds exclusively tailored toward that goal is the ONLY way to have a high performing diamond. JMHO.


The majority of consumers are both logical and flexible. They understand that the top category of cut in diamonds covers a fairly wide range of appearances. Up to a point, you can rely on grades and numbers for screening diamonds, but to select the one which pleases your own eyes you must use your own eyes and mind. The majority of Internet shoppers don't use their eyes for making their choice, but rely on the grading on documents and from what vendors tell them. Sure, you see the one diamond sent to you on approval and likely as not it will look just fine. However, there may have been several others that you might have preferred, but never looked at them. The discrimination of light performance within a single grade of cut may prove beneficial to consumers as well as to retailers and even sightholders.

Again, there are a small number of people diligently shopping for a diamond that specifically PERFORMS at or near the very top. We call these good folks "engineer types". They love numbers and could buy a diamond in the dark if the numbers worked for them. Buying a diamond for these folks is a mathematical and analytic contest, not a romantic event. We need tools for these people that give them what they need.

There is no downside to information of the sort we are offering. A GIA Excellent or an AGS 0 is going to be a nice diamond and have a generally premium price with near certainty. However, I'd bet people will pay a higher premium for measured higher performance light behavior stones over the weaker ones within even one general cut grade.

As long as the process is honest, without a hidden agenda, and readily available, the free market will do as it pleases with information. Being so familiar with this market, I feel able to predict with reasonable certainty how it will react.

Many vendors here including GOG and Whiteflash sell higher performance diamonds right within the top cut grades of AGS and GIA already. Making these diamonds defined objectively will do no harm to the diamonds, consumers or the markets. My experience has been that informed consumers generally are the happier ones.

ImaGem claims their readings of Brilliance Sparkle and Intensity are repeatable to 2% at 2 Sigma of certainty, for those into numbers and grading. Here is a link to the definitions of Brilliance, Sparkle and Intensity: http://www.gemappraisers.com/definitions.htm

Here is the definition of Brilliance, since you asked what 200 meant:

Brilliance: a measure of a stone's overall strength of light return that represents its average light return in the face-up position. This measure is arrived at by computing the mean gray-scale value of all pixels within the girdle portion of a diamond.

200 means that the average of the pixels in the image of the diamond was 200 out of a possible 0 to 255 reading. 0 is total blackness and 255 is total whiteness.

I hope this helps you and everyone who is interested in making sense of what is being offered in this thread.

 

[oldminer]

Quote.....The IMAGEM measures proportions, grades clarity and measures light return performance. What and how does it measure them?

Are you inferring that it is as accurate or more accurate than OGI/ Sarin or Helium.

I keep reading your posts about IMAGEM, and with all that you're claiming it does, guess no one will need to get gemology education, as it appears that IMAGEM will just about perform any tests conceivable about diamonds.

It appears your claiming the IMAGEM is able to do more in separating ranges of the best, better than GIA and AGS has.

ImaGem can measure proportions, measure light return, color grade, fluorescence grade, register the identity of a diamond, and, to an extent, clarity grade. An ImaGem complete installation would offer a high degree of efficiency in a large lab environment and holds the promise of interoperability over vast distances where a diamond would grade the same in any lab, so equipped, while not subject to human grading limitations.

Basically, I am addressing the VeriGem tool which primarily is used to measure light behavior and to Register the identity of a diamond when required. I makes its measurements of physical features such as diameters, and angles by the same techniques employed by its competitors, but with a significant improvement in accuracy. All the competition declines in accuracy as stones get larger while the ImaGem system is very stable in accuracy range from 1/4 carat and larger. 5 micron repeatability at 2 Sigma.

The truth is that high accuracy in physical measurement does not mean a whole lot to ImaGem since we don't build a 3D model with which to compute light behavior. Since we read it directly from the diamond, the measurements are nice to have for re-identification, but hold little significance to performance judgment for us. Those who construct models from measurements need the most accurate measures possible. I have been critical about trusting models built with tools that do not measure as well as Helium or ImaGem. Helium has higher measurement repeatability range of up to 40 microns, per their literature on large diamonds and up to 20 microns on diamonds of the size ImaGem now can measure. So there are differences and therefore some issues and doubt. How much this difference will affect 3D models is what I have questioned. We know the claims on how well Helium handles round diamonds. While I have not tested it, others like Helium and I tend to believe it works as Sergey claims. I have much deeper doubts on how anyone's measuring tools will handle fancy shaped diamonds in order to create proper 3D models with all the nuances of shape that exist, and then how ray tracing or beam tracing programs will work to predict light behavior.

Gemology and gemology education will continue to have importance. Some of the routine lab work will become machine and technology oriented. We will spend more time on colored stone ID work, appraisal work for replacement values, and the less regular tasks of gem grading. The diamond grading business is becoming modernized at long last. ImaGem does claim to be able to separate ranges of the best, more completely and more clearly than GIA or AGS. The method is logical, direct and able to grade any shape.

In the works are Verigem variants for appraisers, gemologists and retailers. The basic tool will provide only Light Behavior grading. A more advanced tool will provide the same plus have the Registration feature. ImaGem will be pitching its offerings to the trade in many ways over the coming months and years. I'm pleased to be playing a role in the process of making the diamond trade a viable business for this relatively young 21st century.

 

[RockDoc]

Photo (c) Courtesy Wendy's
Rockdoc

 

[adamasgem]

Date: 8/17/2006 2:35:57 PM
Author: oldminer



ImaGem can measure proportions, measure light return, color grade, fluorescence grade, register the identity of a diamond, and, to an extent, clarity grade. An ImaGem complete installation would offer a high degree of efficiency in a large lab environment and holds the promise of interoperability over vast distances where a diamond would grade the same in any lab, so equipped, while not subject to human grading limitations.

The truth is that high accuracy in physical measurement does not mean a whole lot to ImaGem since we don''t build a 3D model with which to compute light behavior. Since we read it directly from the diamond, the measurements are nice to have for re-identification, but hold little significance to performance judgment for us. Those who construct models from measurements need the most accurate measures possible. I have been critical about trusting models built with tools that do not measure as well as Helium or ImaGem. Helium has higher measurement repeatability range of up to 40 microns, per their literature on large diamonds and up to 20 microns on diamonds of the size ImaGem now can measure. So there are differences and therefore some issues and doubt. How much this difference will affect 3D models is what I have questioned. We know the claims on how well Helium handles round diamonds. While I have not tested it, others like Helium and I tend to believe it works as Sergey claims. I have much deeper doubts on how anyone''s measuring tools will handle fancy shaped diamonds in order to create proper 3D models with all the nuances of shape that exist, and then how ray tracing or beam tracing programs will work to predict light behavior.

I just noticed on the Imagem newsletter, that you show a sample marguise report. If you took these measurements using Imagem technology, then I think you have a problem.

 

[adamasgem]

This was the sample report from the Imagem newsletter. WOW a marquise that measures 10 by 10 by 6.1. Great accuracy..

 

[Serg]

re:I makes its measurements of physical features such as diameters, and angles by the same techniques employed by its competitors, but with a significant improvement in accuracy.The truth is that high accuracy in physical measurement does not mean a whole lot to ImaGem since we don''t build a 3D model

1) Dave you did not explain HUGE errors in Imagem measurements yet( specially in Crown angle).
2) Imagem declared What task to building accuracy 3D model is more a less simple. Do it. It will show for you real Imagem accuracy and problems with measurements.

 

[RockDoc]

Here''s another image with the marquise as above with SAME REPORT NUMBER, same weight and same shape but now the diamond is vivid BLUE.

How did the white in the same lab report change from colorless to blue. Additionally is the blue stone natural, synthetic, treated or did just magically change color via Photoshop.

The report says diamond shouldn''t there be some disclosure about the above? THe ASSUMPTION IS THAT IT IS NATURAL !
Then you talk about accuracy and repeatability !

PLUS it is split clarity graded and split color graded.

Imagem has also claimed to be able to re-identify diamonds. With such varying conclusions on the reporthow would IMAGEM be able to do this, particularly at the level for evidence in criminal court?

Shocking...

 

[adamasgem]

Re Imagem newsletter and hyperbole. "In addition to the rotational resolution there is one more reason why a profile view may not accurately measure the minimum girdle diameter. All gauging systems on the market use a telecentric lens to capture the profile image of a stone. It is a property of a telecentric lens that it will miss an indented spot on the girdle when viewed in the profile position, and hence minimum girdle diameter measurement will be inaccurate."

Hello, I''d like to see a proof of that statement...

 

[Serg]

Re: The following table shows the repeatability of crown and pavilion angles and proportions for different size stones for a system which has a linear precision of plus or minus 20 microns (in the following calculations the average girdle diameter was kept constant to manage complexity of the impact of linear precision).

Measures 0.25 carat size 0.50 carat size 1 carat size
Crown Angle +/- 0.92 degrees +/- 0.72 degrees +/- 0.58 degrees
Pavilion Angle +/- 0.32 degrees +/- 0.25 degrees +/- 0.2 degrees
Crown percentage +/- 0.49 % +/- 0.385 % +/- 0.31 %
Pavilion percentage +/- 0.49 % +/- 0.385 % +/- 0.31 %
Girdle Thickness +/- 0.49 % +/- 0.385 % +/- 0.31%
Total depth +/- 0.49 % +/- 0.385 % +/- 0.31%
Table size +/- 0.49 % +/- 0.385 % +/- 0.31%

It is looks Imagem researchers simply divided linear precision to diameter. It is wrong( or other words wrong calculations)
For example
Crown , 1 carat size.
20 microns/6400 microns*100=0,3125% In Imagem table is 0,31%
But should be 20 microns *( 1 + 0,15( crown height))/6400*100=0,359375% Much bigger
They need start study theory of errors. Usually They can study it on first course good Physics department

Dave,
All such Imagem suppositions about connection between Maximum linear and angle accuracy Sarin and Helium scanners are wrong.

 

[Serg]

One must consider whether a system allows a direct view of the outline of a stone and the image of a table. This is important since gauging obtained from processing images of direct views of the table and the girdle will have higher accuracy and repeatability than images from the profile view, other things being equal. For example, the following stone with a slightly flat or indented girdle was processed on a machine which viewed the stone from the profile only as well as on a system that had a direct view of the girdle. Readings from the two systems were as follows:

Profile view Direct view
Average girdle diameter 3.62mm 3.615mm
Minimum girdle diameter 3.55mm 3.513mm
Maximum girdle diameter 3.65mm 3.670mm


Due Imagem logic
For Princess with diameter 3.51mm Cut Helium accuracy( and repeatability. Result depends from start position cut in scanner) of diameter should be worse than 50 microns

(Tan( 1.8 degree/2) *3510microns/2)*2=55microns

Each owner Helium can easy check and confirm It is very far from real world.

Dave ,
May be Imagem researchers has not enough skills for conclusions about real accuaracy Sarin and Helium scanners?

 

[oldminer]

Well, a nice litle fire storm overnight built up overnight. This is the kind of entertainment people love to read and learn from. Of course, much of this is beyond my knowledge, but I will get a response from Dr. Aggarwal and report back. For the Pricescopers who are not receiving the ImaGem monthly newsletter, they may need to be informed that some of this now has been taken into this thread by those who do get the newsletter. It was a newsletter that has generated some controversy, so it seems.

Some of the postings are totally wrong for this thread, but what the heck? They get so hopped up can't start a fresh thread of their own. Its going to be okay anyway.

I will tell you all that the measures of the diamonds in the credit card sized program that has been copied here are not totally derived from ImaGem. Only the light behavior grades on these diamonds are ImaGem along with diameter readings. The depth was estimated as no side view was taken.

A second card with limiting conditions and explanations also goes with each product, so the copies are incomplete as shown. It has been a successful program. We think it is leading the way to a new diamond grading level.

 

[Serg]

http://www.imageminc.com/demos/consistencycalculator.html


It is the example of BUG in Imagem calculation becuase due 58.908=43.108+1.2+14.6 Girdle 1.2 has not common part with Crown height.

 

[adamasgem]

Date: 8/18/2006 6:50:47 AM
Author: Serg

Re: The following table shows the repeatability of crown and pavilion angles and proportions for different size stones for a system which has a linear precision of plus or minus 20 microns (in the following calculations the average girdle diameter was kept constant to manage complexity of the impact of linear precision).


Measures 0.25 carat size 0.50 carat size 1 carat size
Crown Angle +/- 0.92 degrees +/- 0.72 degrees +/- 0.58 degrees
Pavilion Angle +/- 0.32 degrees +/- 0.25 degrees +/- 0.2 degrees
Crown percentage +/- 0.49 % +/- 0.385 % +/- 0.31 %
Pavilion percentage +/- 0.49 % +/- 0.385 % +/- 0.31 %
Girdle Thickness +/- 0.49 % +/- 0.385 % +/- 0.31%
Total depth +/- 0.49 % +/- 0.385 % +/- 0.31%
Table size +/- 0.49 % +/- 0.385 % +/- 0.31%


It is looks Imagem researchers simply divided linear precision to diameter. It is wrong( or other words wrong calculations)

For example
Crown , 1 carat size.
20 microns/6400 microns*100=0,3125% In Imagem table is 0,31%
But should be 20 microns *( 1 + 0,15( crown height))/6400*100=0,359375% Much bigger
They need start study theory of errors. Usually They can study it on first course good Physics department


Dave,
All such Imagem suppositions about connection between Maximum linear and angle accuracy Sarin and Helium scanners are wrong.

Sergey.. I had looked at the table also and noted that they stated that they held the Diameter constant, i.e. their approximation had the uncertainty in the diameter as 0.0 microns.

Their example would be a dumbed down MINIMUM uncertainty level.

In reality, each percentage in the table would have a different uncertainty level, based on the numerator used (crown height, depth, girdle thickness, etc..

To first order you can expand the ratio equation

(X + ERROR_X)/(D + ERROR_D) approximately = (X/D + ERROR_X/D)*(1 - ERROR_D/D)

where ERROR_D is assumed
As to their uncertainties in the angles, I wonder how they arrived at the numbers, as there are a multitude of ways to process the profile information, and given that the planes are "overdefined" ( > 3 points used to define the plane) with the data, I believe that angle accuracy between two planes can be less than stated.

My guess is that they just looked at linear error uncertainties and the trig relationships, and did not consider the "overdefined" plane processing.

 

[adamasgem]

Date: 8/18/2006 8:20:24 AM
Author: oldminer
Well, a nice litle fire storm overnight built up overnight.

This is the kind of entertainment people love to read and learn from.

Of course, much of this is beyond my knowledge

, but I will get a response from Dr. Aggarwal and report back.

For the Pricescopers who are not receiving the ImaGem monthly newsletter, they may need to be informed that some of this now has been taken into this thread by those who do get the newsletter. It was a newsletter that has generated some controversy, so it seems.
It is also the hyperbole regarding light metrics using an undefined envirionment. The widest "Discrimination" is easily done with high angle lighting, but it doesn''t necessarily equate to best overall performance, only performance in THAT UNKNOWN ENVIRIONMENT.

Some of the postings are totally wrong for this thread, but what the heck? They get so hopped up can''t start a fresh thread of their own. Its going to be okay anyway.

I will tell you all that the measures of the diamonds in the credit card sized program that has been copied here are not totally derived from ImaGem. Well, since they were on an Imagem Newsletter, shouldn''t one expect they were.? Only the light behavior grades on these diamonds are ImaGem along with diameter readings. The depth was estimated as no side view was taken.

A second card with limiting conditions and explanations also goes with each product, so the copies are incomplete as shown. It has been a successful program. We think it is leading the way to a new diamond grading level. I guess it is whatever "sells".

But the examples shown surely didn''t ring my chimes, I didn''t get a warm and fuzzy feeling. Someone should sanity check the newsletters more closely.

After I saw the newsletter, I decided to write up a covariance analysis simulation of the possible uncertainty levels attainable based on profile information, if the processing is done optimally. You can define a plane with three or more points or using two or more non congruent lines. The more data used, the better the estimates tend to be.

 

[littleroman]

I agree with this topic. I am definitley a newbie but had my diamond appraised by a true professional and one of the most repected gemologists in the NYC area. I was totally surprised at what she had to say. She told me she loved the cut of my stone. I was surprised by this because I posted the numbers here and everyone told me this was wrong that was wrong and it was a decent at best. She then went on to explain that you can have the best numbers in the world and still have a "dead" diamond. She told me she had an AGS 0 in the other day, and that she would much rather have my stone because the cut fit the stone and it was emitting fire and brilliance that she rarely sees. I was completely surprised and of course happy !

 

[oldminer]

Dr. Aggarwal has been watching this thread and its now radical distance from the original subject. It still makes good reading and will be useful for learning.

The reason one uses a Telecentric lens is gain constant magnification within the depth of field and the elimination of perspective error. These features are not found in a conventional lens. One can find a very nice example and explanation on page 211 of the Edmund Optic catalog.

Using only a side view, one would only catch the correct diameter of a round diamond that had a flat spot or an indented girdle by accident, even using 800 scans (every 0.45 degrees). You'd be way less likely to catch the right spot using 0.9 degrees or 1.8 degree scans.

The table that was copied previously shows the difference in a ROUND diamond using a side view versus a top view showing the exact and entire girdle image.

Average girdle diameter 3.62mm side view 3.5mm top view
Minimum girdle diameter 3.5mm side view 3.3mm top view
Maximum girdle diameter 3.5mm side view 3.MM top view

For whatever reason, Sergey jumped on that using a PRINCESS cut example, which is totally off the point. The diameter of a round diamond is quite a different animal than measuring the sides of a princess cut.

Imagem detects and measures the diameter of a ROUND diamond without regard to the angular orientation to the lens system because of using a top view. No feature of diameter is hidden to the lens as may happen in a side view. The chart above is an actual example for our records. This is why ImaGem does not exactly match Sarin, Ogi or Helium measures. It is a fact.

ImaGem further uses the face-down table view to then accurately orient the diamond, round, princess, or marquise into the exact angular relation ship with the lens to take correct side view measures to within about 0.1 degrees of orthogonal. This way, we combine the knowledge gained from the top to plant the diamond into the side view program in a repeatable manner. This method gives increased high repeatability/ consistency and accuracy.


Then we have the following quoted back to us by Sergey:

Re: The following table shows the repeatability of crown and pavilion angles and proportions for different size stones for a system which has a linear precision of plus or minus 20 microns (in the following calculations the average girdle diameter was kept constant to manage complexity of the impact of linear precision).


Measures 0.25 carat size 0.50 carat size 1 carat size
Crown Angle +/- 0.92 degrees +/- 0.72 degrees +/- 0.58 degrees
Pavilion Angle +/- 0.32 degrees +/- 0.25 degrees +/- 0.2 degrees
Crown percentage +/- 0.49 % +/- 0.385 % +/- 0.31 %
Pavilion percentage +/- 0.49 % +/- 0.385 % +/- 0.31 %
Girdle Thickness +/- 0.49 % +/- 0.385 % +/- 0.31%
Total depth +/- 0.49 % +/- 0.385 % +/- 0.31%
Table size +/- 0.49 % +/- 0.385 % +/- 0.31%


The part highlighted in sky blue is crucial to the situation. This was done not to hide anything, but to make the chart easy enough to comprehend and meaningful. Keeping one variable constant makes the results simpler. Of course, in the real world, the measure of diameter may vary within the tolerances that exist, but then we'd have many charts, not just one. We are aware of this and no one is hiding that this is a complex subject. Fear not, the bases are covered. There is no content to this argument. THIS is AN EXAMPLE not an entire set of possiblilities.

Quoting Marty Haske below:

".......but it doesn't necessarily equate to best overall performance, only performance in THAT UNKNOWN ENVIRONMENT."

We agree that the ImaGem environment is more or less UNKNOWN, but it is a "Normal Lighting Environment" in scientific terms. We get results that correspond to human perception and we find some very large labs and businesses interested in becoming users. These people are testing equipment, asking direct questions and we see some ready to adopt new technology. I will have the VeriGem with me in San Diego at NAJA and GIA Symposium. If you have a diamond that is off interest to you to see how it scores, please bring it to me for a scan.


Finally, the best and last part of the answer. It is rather humorous. The automatic consistency calculator is doing its job just as it should. It is the users who don't understand the point of the calculator. You can enter any nonsense you wish on the left. The crucial results are either the word YES or NO on the far right column. NOTE: the far right column on one example says "YES" meaning this situation is REALISTIC and POSSIBLE. The other example says "NO" meaning the situation is NOT CONSISTENT with reality and is an IMPOSSIBLE set of values.

It is a geeky laugh at best, but it is a failure to understand the calculator's use. We can't turn unreality into reality unless we dummy down the results. ImaGem does not dummy down results but many of us know that at least one major player is doing that....and this is not directed at any participating here, so Sergey you are not the target.

I hope everyone reading and participating here feels my responses were properly directed and to the points that have been raised. There is no agenda to hide anything other than trade secrets and intellectual property. These won't have an ill effect on how well a device works. It is up to the trade to adopt or not adopt a technology. I know some of the responses may seem like a personal attack on me, but I choose to view them as business and not personal. I hope that others consider their words before hitting "SUBMIT" as much as I generally do. Occasional failings aside, I generally make a good effort at being fair to those who take the time to read what I have posted.