Differences in Sarin and AGS???

[angeline]

Hi esteemed knowledgable diamondphiles!

I have been looking at a diamond (a WF ACA) and noticed that the AGS report and the Sarin differ quite a bit. Can someone tell me which one is more accurate? Using the Sarin angles for example the diamond scores a 1.3 XXXVG on the HCA. Using the AGS angles etc it scores a 1.7 XVGVGVG. The Sarin also ists the weight as 1.530 and the AGS lists it as 1.538. That seems a bit of a difference!

Thanks for any help!

a

 

[oldminer]

AGS uses a Sarin. There is a problem of unknow importance with creating models to estimate light perfomance based on questionable measurements. Some will tall you the difference is negligible and others won''t be so bold to assume it has no meaning. Models are created to siulate reality. If reality and the simulation differ, how useful is the model?

 

[kenny]

No machine is perfect.
All test equipment is made to a certain level of precision, and to display a given number of significat figures.

I work in engineering.
We routinely ignore the last digit that any instrument reports.

If you measure the same thing on the same instrument on seven consecutive days you may get seven slightly different numbers.
Nothing is broken - except the expectation of perfection on the part of the person reviewing the data.
(The "truth" is likely near the average of those seven numbers.")

If the equipment was designed to give more digits and we saw two HCAs of the same stone that were 1.003 and 1.007 someone would worry about THAT discrepancy too.

 

[RockDoc]

Date: 8/13/2006 1:00:51 PM
Author:angeline
Hi esteemed knowledgable diamondphiles!

I have been looking at a diamond (a WF ACA) and noticed that the AGS report and the Sarin differ quite a bit. Can someone tell me which one is more accurate? Using the Sarin angles for example the diamond scores a 1.3 XXXVG on the HCA. Using the AGS angles etc it scores a 1.7 XVGVGVG. The Sarin also ists the weight as 1.530 and the AGS lists it as 1.538. That seems a bit of a difference!

Thanks for any help!

a

AGS uses the Sarin most commonly, but does have Helium machine too.

Which AGS report are you comparing it too?.... The DQD or the DQR ? New one or used one? ( I would assume that if the stone is an ACA - it has a DQD report). If you have a DQD with a cut grade on it, or better yet the newer one with light performance rating on it, I''d give that more weight than the HCA, as the HCA doesn''t take minor facets into consideration and assumes all the stones are symmetrical. Also check to make sure as you enter numbers that they remain the same, as if they are not "locked" they can "change" on the HCA and Diamond Calc.

Plus if the ACA stone you''re looking at has the new cut grade rating, it''s proportions and light return are measured, while in the HCA only proportional formulas are used to determine/estimate the cut quality.

See this thread too. https://www.pricescope.com/community/threads/is-your-stone-really-an-ags-000.49351/

As Kenny wrote, machines that measure, when measuring very small increments, are going to have an acceptable tolerance and variance.

As far as angles are concerned........ remember variance of a few tenth of a degree can really be minor, as a circle has 360 full degrees. So a couple tenths of ONE degree is darn small.


Rockdoc

 

[angeline]

Thanks everyone for your information and help, I really appreciate it. I wasn''t really worried about the HCA, it was more just the fact that I saw two different weights reported and I wondered which was more accurate. I know these are tiny differences in numbers but hey, that''s what everyone obsesses about on these boards isn''t it?

I''ll read that link Rockdoc, thanks!

a

 

[RockDoc]

Date: 8/13/2006 10:42:36 PM
Author: angeline
Thanks everyone for your information and help, I really appreciate it. I wasn''t really worried about the HCA, it was more just the fact that I saw two different weights reported and I wondered which was more accurate. I know these are tiny differences in numbers but hey, that''s what everyone obsesses about on these boards isn''t it?

I''ll read that link Rockdoc, thanks!

a

Hi Angeline.

I didn''t answer the "main" question about the differences in carat weight. So here goes.


When on of the proportion non-contact units states the weight ( such as OGI/ Megascope or Sarin) we do insert the reported carat weight based on weighing the stone, which is what the labs do.

In the OGI and Sarin software, the weight is a calculated weight. This is estimated by take the average length width )( or diameter measurement) times the depth measurement etc, which is a formula that estimates the carat weight by volume rather than actual weight. It is my belief this is done to prevent someone who weighs a CZ ( which weighs more than diamond) and reconciles the weight by formula, so that if there is a difference the person doing the analysis can take a better look to make sure he has a real diamond.

I also wonder why OGI and Sarin don''t report both weights ( and identify which is which) or at least state in their software that it is based on a formula calculation, rather than an actual weight in the form that they print out.

So as far as actual carat weight determined by accurate, and actual weighing of the stone on a carat scale, rely on the weight from the lab.

Rockdoc

 

[angeline]

Aha!! That makes perfect sense now Rockdoc! I was thinking that there''s no point reporting that last decimal point if it has no accuracy. But if they are actually calulated in different ways then that makes perfect sense now to me. Thanks! Cool! I don''t like not knowing things

a

 

[Garry H (Cut Nut)]

Date: 8/13/2006 11:42:44 PM
Author: angeline
Aha!! That makes perfect sense now Rockdoc! I was thinking that there''s no point reporting that last decimal point if it has no accuracy. But if they are actually calulated in different ways then that makes perfect sense now to me. Thanks! Cool! I don''t like not knowing things

a

Angeline 1.530 and 1.538 are both 1.53ct under international diamond standards.
1.539 = 1.54ct

We only round up when the third decimal is a 9.

I guess that is a hangover from days when scales were a bit less accurate.

AGS also are one of the only labs that have a helium from OctoNus - the most accurate scanner - although they also use Sarin

 

[JohnQuixote]

Good answers. I'd add that Sarin's reported error is .2 degrees angular and .02% linear.

GIA reports carat weight to 2 decimal places on their reports. Since AGS reports it to 3 we choose to include the thousandth-of-a-ct in our local scan.

Keeping such a difference in perspective, an international ounce = 28.35 grams.
A ct = 0.20 of a gram...So 0.001 ct = 0.0002 of a gram, or 0.000007 of an ounce.

On that level many things can influence such measure. Whether Helium, Sarin, Ogi or Imagem - these non-contact scanning devices are extraordinary to have the consistency they do have (and the guys who used to have to do all this by hand are quick to remind us of that!).

I hope this is all helpful Angeline.

 

[Rhino]

Interesting thread and demonstrates the reason why GIA has used the little bit of rounding they have on their reports. No 2 Sarin''s are always identical.

Peace,

 

[Regular Guy]

Date: 8/14/2006 9:46:27 PM
Author: Rhino
Interesting thread and demonstrates the reason why GIA has used the little bit of rounding they have on their reports. No 2 Sarin's are always identical.

Peace,

Jonathan,

I'm not following this line of thought, would you care to explain?

P.S. I think it's frequently helpful to get a fresh view on things. For those of us not keen on researching, and who allow google to do our work for us, you might try, as I did, to put together: "measurement error" and rounding. The second item seemed substantive, and is here. Example #1 is I think on point. But...you may have another point of view on this.

 

[JohnQuixote]

I'd prefer another round to another rounding discussion

but it's safe to say some are comfortable with GIA's reporting and others feel the lab should give as much precision as possible.

For those who didn't get it the first several times,

GIA rounds the numbers on their grading reports to the nearest .2 CA, .5 PA and 5% stars & lower halves, rather than reporting the actual Sarin numbers.

I hope Aljdewey doesn't mind if I borrow her counterpoint from a few days ago. I thought it well-stated... If she does mind, I'm in serious trouble.

Date: 8/8/2006 6:08:37 PM
Author: aljdewey

I get it.......since everyone's machine varies a little, why sweat the small stuff? But they aren't looking at the aggregate effect.

Going to your example.....Bill's Sarin isn't identical to GIA's Sarin. So, Bill's Sarin reports a 40.7 crown angle and GIA reflects a 40.9. However, since GIA doesn't like even numbers, now they round that up to 41. They further amplified the difference by rounding.

Then, on the same diamond, Bill's Sarin shows a 34.6 crown. GIA shows 34.7, but they round it up to 35. There's another amplified difference.

By the time you get done amplifying the already inherent differences times all the things they round, the data becomes meaningless.

Their approach is akin to saying 'since all devices measure with a degree of error anyway, it's not important to be exact at all.' I disagree with this line of thinking. The fact that nothing can be 100% perfect all the time isn't a valid reason to get sloppy and lenient on the standards.

We can acknowledge that perfection isn't achievable, but the act of at least striving for it produces better results than throwing hands in the air and saying 'ah - close enough.'

Original thread: https://www.pricescope.com/community/threads/stone-with-hca-score-under-1-0-tends-to-have-very-poor-performance-is-this-true.49102/

 

[RockDoc]

If one looks at the GIA graphic where the proportions are reported there is a notation.

That caption has the word "ACTUAL" stated.

If they are rounded up - how are they ACTUAL?????

I guess the question is how much variance or tolerance would you consider when using the term ACTUAL.

AGS does not say actual.

I''m not sure that this is the proper way to express results, and I think many of your would agree.

Would it be so bad to more factually express the results ( if you HAVE to put that CAPTION there ) with terminology that is accurate? "SUCH AS - PROPORTION MEASUREMENTS CAN VARY, AND ARE EXPRESSED AS AN AVERAGE FOR EACH FACET GROUP,AND THE MEASUREMENTS REPORTED ARE ROUNDED UP"

Being a stickler for detail, they should also state what numbers they rounded UP or DOWN "TO" and how much each facet group the rounding up is.

I think AGS has done this better, but even with in their reports they need to say the angles/ %''s reported are averages.


Rockdoc

 

[angeline]

I appreciate everyone''s replies which are more detailed than I ever hoped for! However as we''re getting into this topic, I have a thought or two... Coming from an experimental physics background, machines used for measurement (and we''re talking MUCH smaller than 1/1000''s of a mm, think nanometers) have a stated accuracy. So if measurements are taken to say 2 decimal places, that last digit is accurate to within +/- .5 of the third decimal place if you get what I mean. eg a measurment of .27mm means .27mm +/- .005mm, or the measurement could be anywhere within .265 to .275.

What I don''t get is
1: why rounding down in weight meas. occurs until the value is >.9
2: if a machine can''t reproduce a measurement consistently to a certain decimal place then that decimal place isn''t accurate and should be rounded according to normal scientific convention as in my small example above. These Sarin machines should have a certain stated accuracy that is reproducible to THAT decimal place. Any further decimal places are meaningless.

just my .02

a

 

[He Scores]

Date: 8/13/2006 1:17:22 PM
Author: kenny
No machine is perfect.
All test equipment is made to a tolerance.

I work in engineering.
We routinely ignore the last digit that any instrument reports.

If you measure the same thing on the same instrument on seven consecutive days you may get seven slightly different numbers.
Nothing is broken - except the expectation of perfection on the part of the person reviewing the data.
(The ''truth'' is likely near the average of those seven numbers.'')

If the equipment was designed to give more digits and we saw two HCAs of the same stone that were 1.003 and 1.007 someone would worry about THAT discrepancy too.

Kenny...I like that..."nothing is broken except the expectation of perfection on the part of the person reviewing the data."



Bill Bray
Diamond Cutter

 

[Rhino]

Date: 8/15/2006 3:17:45 AM
Author: RockDoc

If one looks at the GIA graphic where the proportions are reported there is a notation.

That caption has the word ''ACTUAL'' stated.

If they are rounded up - how are they ACTUAL?????

I guess the question is how much variance or tolerance would you consider when using the term ACTUAL.

AGS does not say actual.

I''m not sure that this is the proper way to express results, and I think many of your would agree.

Would it be so bad to more factually express the results ( if you HAVE to put that CAPTION there ) with terminology that is accurate? ''SUCH AS - PROPORTION MEASUREMENTS CAN VARY, AND ARE EXPRESSED AS AN AVERAGE FOR EACH FACET GROUP,AND THE MEASUREMENTS REPORTED ARE ROUNDED UP''

Being a stickler for detail, they should also state what numbers they rounded UP or DOWN ''TO'' and how much each facet group the rounding up is.

I think AGS has done this better, but even with in their reports they need to say the angles/ %''s reported are averages.


Rockdoc

Good input Rocky.

 

[Rhino]

Hi Ira,

I think it best for me to answer via Alj''s response since it appears I missed it in the other thread. My comments will be in bold.

Date: 8/15/2006 2:03:18 AM
Author: JohnQuixote
I''d prefer another round to another rounding discussion

but it''s safe to say some are comfortable with GIA''s reporting and others feel the lab should give as much precision as possible.

For those who didn''t get it the first several times,

GIA rounds the numbers on their grading reports to the nearest .2 CA, .5 PA and 5% stars & lower halves, rather than reporting the actual Sarin numbers.

Hey John... I think you mean .2 on the PA and .5 on the CA.

I hope Aljdewey doesn''t mind if I borrow her counterpoint from a few days ago. I thought it well-stated... If she does mind, I''m in serious trouble.

Date: 8/8/2006 6:08:37 PM
Author: aljdewey

I get it.......since everyone''s machine varies a little, why sweat the small stuff? But they aren''t looking at the aggregate effect.

Going to your example.....Bill''s Sarin isn''t identical to GIA''s Sarin. So, Bill''s Sarin reports a 40.7 crown angle and GIA reflects a 40.9. However, since GIA doesn''t like even numbers, now they round that up to 41. They further amplified the difference by rounding.

Then, on the same diamond, Bill''s Sarin shows a 34.6 crown. GIA shows 34.7, but they round it up to 35. There''s another amplified difference.

Actually both of those would be rounded to 34.5 but I see where you''re headed with this reasoning.

By the time you get done amplifying the already inherent differences times all the things they round, the data becomes meaningless.

Not really if you take the time to understand the reasoning behind the cut grading system as a whole which I''ll expound upon below moreso.

Their approach is akin to saying ''since all devices measure with a degree of error anyway, it''s not important to be exact at all.'' I disagree with this line of thinking. The fact that nothing can be 100% perfect all the time isn''t a valid reason to get sloppy and lenient on the standards.

Sloppy and lenient according to whom?

We can acknowledge that perfection isn''t achievable, but the act of at least striving for it produces better results than throwing hands in the air and saying ''ah - close enough.''

Original thread: https://www.pricescope.com/community/threads/stone-with-hca-score-under-1-0-tends-to-have-very-poor-performance-is-this-true.49102/

You see, here''s the deal. We live in a world here on PS that is perhaps more anal than the rest of the world.

We are sticklers for detail and drool at the thought of perfection. When I find cherry stones with ideal slope and azimuth angles I LOVE IT.

Let me make one thing clear ... I am for as much detail as possible.

When you have a cut grading system based on observation testing and face up appearance and you''ve been in this trade for as long as I have you get to know that when it comes to face up appearance ... (and I''m talking on a practical level now), if you put a diamond with 34.68 crown angles next to a diamond with 34.3 crown angles you will not see a difference. If we take 2 diamonds and both have 41 degree pavilion angles, and I lay a stone with 34.8 or 35.2 crown angles side by side to it ... guess who''ll be able to see the difference? Answer: Nobody.

.1 variance in either direction on the pavilion is a rats hair and .25 degrees either way on the crown is equally so. Alj ... we can take the greatest expert eyes we know of and I can show them this comparison, guess who''ll be able to tell me what stones have what *precise* angle combos within that tolerance? Nobody on God''s green earth can because then it would depend on who''s Sarin was being used!

LOL

Seriously ... the hootin and hollaring about the infintessimal degree of rounding they are doing are not, by any means unreasonable.

Would I prefer it to be more exacting? Yes. Are they being unreasonable? Definitely not because nobody here would be able to visibly see the difference from this minutae in the rounding.

Now ... if there was a visible difference we all could note from a 34.8 to a 35.2 crown angle you''d have a case.

Hope that helps.

 

[Rhino]

Date: 8/15/2006 4:20:56 PM
Author: He Scores

Date: 8/13/2006 1:17:22 PM
Author: kenny
No machine is perfect.
All test equipment is made to a tolerance.

I work in engineering.
We routinely ignore the last digit that any instrument reports.

If you measure the same thing on the same instrument on seven consecutive days you may get seven slightly different numbers.
Nothing is broken - except the expectation of perfection on the part of the person reviewing the data.
(The ''truth'' is likely near the average of those seven numbers.'')

If the equipment was designed to give more digits and we saw two HCAs of the same stone that were 1.003 and 1.007 someone would worry about THAT discrepancy too.

Kenny...I like that...''nothing is broken except the expectation of perfection on the part of the person reviewing the data.''



Bill Bray
Diamond Cutter

Ditto that Bill and Kenny.

 

[Rhino]

Hi Angeline,

To answer your questions...

What I don''t get is
1: why rounding down in weight meas. occurs until the value is >.9

That IS a good question. Frankly if it were my system if it were .5 and higher in weight it should be rounded to the next. Either that or do like AGS and report down to 1/1000th of a point.

2: if a machine can''t reproduce a measurement consistently to a certain decimal place then that decimal place isn''t accurate and should be rounded according to normal scientific convention as in my small example above. These Sarin machines should have a certain stated accuracy that is reproducible to THAT decimal place. Any further decimal places are meaningless.

just my .02

a

good points angeline.

That''s the reason they''ve rounded as they have. All these scanners are only so accurate from one to the next. Some upkeep their calibrations while others don''t and that''s generally where the greatest discrepancies will reside. Hence the rounding issue.

Hope that helped.

Kind regards,

 

[He Scores]

From the For What it''s Worth Dept.


I took a raw data file for a diamond from the Sarin data needed to generate BrayScores and increased the angular measurements to the maximum error reported by Sarin which is +-.2degree. i.e. 40.7 became 40.9.

When this was done to all the crown and pav angles the score was lowered from a 712 to a 689. This represented a 4.4% difference.

The file was saved.

The file was then altered to reflect the linear error as reported by Sarin which is +-20 microns. This was factored into the gblz percentages, ghlv percentages and the gmins.
The file was then uploaded to the BrayScore web module and a new score was generated, 661. This represented a 7.1% difference.

This was a quick brief study and may have some errors...it certainly isn''t a study as worthwhile as Sniper would do.


Bill Bray
Diamond Cutter

 

[He Scores]

Also, when Rhino said: "if you put a diamond with 34.68 crown angles next to a diamond with 34.3 crown angles you will not see a difference" I have to agree with him when he says you. However, when it comes to diamondtaires, my research has shown that a 6% difference in a BrayScore in a top made (average nice ideal cut) stone, approx. half the experts will interchange the stones.

There has to be an established acceptable tolerence for these measuring devices, just like we settled on 10X for clarity grading.

Frankly, I think as a cutter and a cut anaylist Sarin provides sufficient ''accuracy'' and ''repeatability'' for the day to day business of selling and buying diamonds.


Bill Bray
Diamond Cutter

 

[tlow]

This may be a little off topic, but related. Sorry, if I am asking newbie questions...

Where does the GIA and/or AGS reports get the CA and PA numbers from. Meaning they come up with a single value, is that value the average, mean, median, mode, weighted average, etc.? depending on what statistical analysis one uses, more error creeps in, right?

 

[whatmeworry]

no there is actually less error in the average (mean) than in a single angle measurement (if the angle measurements are independent from each other). Say each pav angle is +/- 0.2 degrees, then the reported average of all 8 pav angles might be +/- 0.07

 

[aljdewey]

Date: 8/15/2006 5:03:13 PM
Author: Rhino
You see, here's the deal. We live in a world here on PS that is perhaps more anal than the rest of the world.

We are sticklers for detail and drool at the thought of perfection. When I find cherry stones with ideal slope and azimuth angles I LOVE IT.

Let me make one thing clear ... I am for as much detail as possible.

When you have a cut grading system based on observation testing and face up appearance and you've been in this trade for as long as I have you get to know that when it comes to face up appearance ... (and I'm talking on a practical level now), if you put a diamond with 34.68 crown angles next to a diamond with 34.3 crown angles you will not see a difference. If we take 2 diamonds and both have 41 degree pavilion angles, and I lay a stone with 34.8 or 35.2 crown angles side by side to it ... guess who'll be able to see the difference? Answer: Nobody.

.1 variance in either direction on the pavilion is a rats hair and .25 degrees either way on the crown is equally so. Alj ... we can take the greatest expert eyes we know of and I can show them this comparison, guess who'll be able to tell me what stones have what *precise* angle combos within that tolerance? Nobody on God's green earth can because then it would depend on who's Sarin was being used!

LOL

Seriously ... the hootin and hollaring about the infintessimal degree of rounding they are doing are not, by any means unreasonable.

Would I prefer it to be more exacting? Yes. Are they being unreasonable? Definitely not because nobody here would be able to visibly see the difference from this minutae in the rounding.

Now ... if there was a visible difference we all could note from a 34.8 to a 35.2 crown angle you'd have a case.

Hope that helps.

I hate to point this out.....but it's those anal people who drive the market for ideal stones in the first place.

If diamonds were Animal-farm-esque, there would be no reason to seek excellence, would there?

So, I guess your "new" position is 'a little bit here and a little bit there and a little bit over there, too isn't going to be appreciable to the eye.' Let me then ask, so will this be the new credo for stones that are very, very, very, very, very infintessimally painted, too? That when it's such a tiny amount, no big deal? Or will even the slightest little touch of painting continue to make you press the Defcon 1 button?

What seems to be missing in your position above is the consideration of the aggregate. One measurement being a little bit off isn't a huge deal, but multiple measurements being rounded does compound. Are they noticeable to the eye? Unless you're considering ALL the rounding and the aggregate effect of it, I don't see how anyone could assert that it wouldn't make a visible difference.

Honestly, the argument that "it's ok to round because no machine is perfect and every Sarin machine is different"......personally speaking, I feel that's a cop-out. GIA is not the only lab faced with the Sarin/OGI/whatever-the-device-of-the-moment-is variations or margins of error; any other lab is faced with the same conditions, so why is GIA the only one using it as an excuse to round?

Incidentally, since they still must use some measuring device as the starting point from which rounding then occurs, rounding does nothing to eliminate the "margin of error" issue. As long as they are still using Sarin/OGI/whatever to arrive at the 40.7 pavilion (which they will then round to 40.8 because they have suddenly developed some peculiar aversion to odd numbers), they don't solve the variation issue through rounding.....all they do is amplify it. The original measurement is subject to margin of error, and the adjusted figure compounds that margin of error.

Again, Bill's Sarin measures 34.6 crown, and since he doesn't round, it's reported as 34.6. Because of margin-of-error variation, GIA's machine measures 34.8.....but if it's 34.8, it gets rounded to 35. If your argument is "precision is impossible since everyone's machine isn't exactly calibrated/precise", my response is "yes, but a .2 crown variance is much less margin of error to me than a .4 variance due to rounding!" Rounding *doubles* that lack of precision......how is that helpful???????????

Devil's advocate for a moment, though. Assume for a moment that what you claim is so....that no one will see a difference from rounding. Million dollar question: then why do it? Why round at all? Your argument is that 34.7 is just as good as 34.9. If so, why not just report the 34.7 measured and leave it at that? What is the purpose of changing the number if it won't make any difference---improvement OR detraction, as you claim? It takes an extra step to measure something and THEN make an adjustment (which you claim makes no visual difference). Doing something--especially making an additional step---just for the sake of doing it makes no sense. If there weren't some advantage to SOMEONE, there would have been no reason to do it.

How does rounding potentially benefit the consumer? I can't think of a single way that consumers would benefit from the practice of rounding, other than false sense of thinking that their stones are more elite than they really are. (In the absolute best case scenario, there is no difference and they don't lose anything....but nor do they benefit.)

How does GIA potentially benefit from rounding? I can think of a few possibilities:

1) it makes it much harder for consumers to compare apples to apples when considering both GIA and AGS stones. That difficulty and confusion certainly would potentially benefit GIA since they are the more widely known lab. If a customer cannot definitively determine which side is more accurate, the default will always benefit the more widely known (GIA in this case).

2) I suspect that rounding means that stones that would otherwise miss the "GIA ex" mark would then qualify. With this as an incentive to dealers, it certainly makes dealers want to put more marginal stones through GIA because there is greater chance of getting the EX grading and the associated $$ premium.

Why do they choose to round? What does it accomplish that measured data doesn't? I've yet to hear any reasonable explanation for it. I fail to see one possible advantage to the customer by adopting this practice.....

I'm really hoping that other experts who support the GIA rounding position will chime in to offer some insights on this.

 

[RockDoc]

2) I suspect that rounding means that stones that would otherwise miss the "GIA ex" mark would then qualify. With this as an incentive to dealers, it certainly makes dealers want to put more marginal stones through GIA because there is greater chance of getting the EX grading and the associated $$ premium.

ALJ


BINGO!

Very GOOD ALJ!

Rockdoc

 

[angeline]

alj...

 

[Rhino]

Date: 8/15/2006 9:17:35 PM
Author: He Scores

Also, when Rhino said: ''if you put a diamond with 34.68 crown angles next to a diamond with 34.3 crown angles you will not see a difference'' I have to agree with him when he says you. However, when it comes to diamondtaires, my research has shown that a 6% difference in a BrayScore in a top made (average nice ideal cut) stone, approx. half the experts will interchange the stones.

There has to be an established acceptable tolerence for these measuring devices, just like we settled on 10X for clarity grading.

Frankly, I think as a cutter and a cut anaylist Sarin provides sufficient ''accuracy'' and ''repeatability'' for the day to day business of selling and buying diamonds.


Bill Bray
Diamond Cutter

Definetely Bill. As pointed out in this thread no technology is *perfect*. Is it sufficient for the job? Absolutely.

Peace,

 

[Rhino]

Hi Alj,

Now where''s my dancing shoes?

Date: 8/16/2006 12:23:31 AM
Author: aljdewey

I hate to point this out.....but it''s those anal people who drive the market for ideal stones in the first place.

If diamonds were Animal-farm-esque, there would be no reason to seek excellence, would there?

A person doesn''t necessarily have to be anal to enjoy and appreciate top make stones. Just those folks who are looking for the best looking diamonds. The reason "cut" never took off for as long as it has is because people weren''t educated on the subject. If we want to get as anal as you are suggesting then lets take your theory to its logical conclusion. Anything other than a Helium Report should be disregarded.

So, I guess your ''new'' position is ''a little bit here and a little bit there and a little bit over there, too isn''t going to be appreciable to the eye.'' Let me then ask, so will this be the new credo for stones that are very, very, very, very, very infintessimally painted, too? That when it''s such a tiny amount, no big deal? Or will even the slightest little touch of painting continue to make you press the Defcon 1 button?

Apparently you haven''t read a word I''ve said on this subject. I have said, in fact in a response to you in this thread, that not all painting is bad or should be categorized the same. I even linked you to the GIA chart showing what degrees of painting and digging are getting dinged. You are the one who is putting these words in my mouth. Words I have never uttered. Page 2 on this thread is specifically where I answered you. Interestingly enough, regardless of my rather clear words, later in that thread it is again said that GIA is mass grading all painting. I hope this is the last time I have to correct this. No sky is falling. No Defcon 1 button. You are amplifying the issue and regardless of what I''ve clearly and repeatedly stated, my perspective and words are still being skewed. PLEASE read my words in that thread again so you are no longer confused about my position.

What seems to be missing in your position above is the consideration of the aggregate. One measurement being a little bit off isn''t a huge deal, but multiple measurements being rounded does compound. Are they noticeable to the eye? Unless you''re considering ALL the rounding and the aggregate effect of it, I don''t see how anyone could assert that it wouldn''t make a visible difference.

I find this arguement amusing because you are generally arguing for *practicality* ... (ie you argue for SI''s over VS''s ... why? becuase in SI they''re not visible to the eye, yet in a critical review of clarity VS clearly wins ... etc. I understand and appreciate both arguements) Interestingly the shoe is on the other foot. Again ... if we take your above arguement to its logical conclusion then anyone offering a Sarin that disagrees with an AGS Report or even more precise, a Helium scan should be disregarded because Sarin''s are not identical from machine to machine. However even with the slight differences found in Sarin''s .1 or .2 variance etc. I still maintain that nobody on this planet would be able to detect the differences with their eyes. LOL... and this coming from the SI queen!

Do you just like to argue with me Alj?

Honestly, the argument that ''it''s ok to round because no machine is perfect and every Sarin machine is different''......personally speaking, I feel that''s a cop-out. GIA is not the only lab faced with the Sarin/OGI/whatever-the-device-of-the-moment-is variations or margins of error; any other lab is faced with the same conditions, so why is GIA the only one using it as an excuse to round?

What I''m about to say is not the "official GIA answer" but common sense tells me they are thinking of the industry as a whole and all the Sarin/OGI machines out there on the market. If we take your argument to its logical conclusion and considering the anally retentive, then if any Sarin/OGI machine disagreed with GIA''s unrounded measurements (should they choose to change their mind and provide that, which btw I would not object to) then if a consumer ... as the one who started this thread may view any Sarin that disagrees with GIA''s as being not reliable. Perhaps not this poster perse, but it would open up a pandora''s box of issues much greater than we are discussing here. As someone who owns non contact scanners from each of the companies manufacturing these, I can tell you (as Bill Bray has expressed) the varying Sarin''s on the market report the results with sufficient accuracy. So if Bill Lieberum''s Sarin says 34.3 crown angles and mine says 34.6 they will both agree with GIA''s rounded 34.5. Is there a visible difference from 34.3 to 34.6? Absolutely not. The sky is certainly not falling ... again.

Incidentally, since they still must use some measuring device as the starting point from which rounding then occurs, rounding does nothing to eliminate the ''margin of error'' issue. As long as they are still using Sarin/OGI/whatever to arrive at the 34.7 pavilion (which they will then round to 34.8 because they have suddenly developed some peculiar aversion to odd numbers), they don''t solve the variation issue through rounding.....all they do is amplify it. The original measurement is subject to margin of error, and the adjusted figure compounds that margin of error.

Question: Enough to make a visible difference to the eye?

Again, Bill''s Sarin measures 34.6, and since he doesn''t round, it''s reported as 34.6. Because of margin-of-error variation, GIA''s machine measures 34.8.....but if it''s 34.8, it gets rounded to 35. If your argument is ''precision is impossible since everyone''s machine isn''t exactly calibrated/precise'', my response is ''yes, but a .2 crown variance is much less margin of error to me than a .4 variance due to rounding!'' Rounding *doubles* that lack of precision......how is that helpful???????????

If there is a discrepancy that would cause a stone to to fall from an Ex grade to a VG, to me that would be an issue and NOT helpful. If that is the case, then this is a good point. We do happen to check each and every stone we measure and compare those results to the rounding done in the FacetWare which we post with each stone. To date we have not found any discrepancies used in your hypothesis. GIA is starting on a premise that implies that all Sarin''s, (while not exact) are precise enough that the little bit of rounding that GIA is doing will all agree. So if Bill''s Sarin is getting a 34.6 crown angle, My Helium and Sarin shows a 34.3, GIA''s rounded Sarin of 34.5 is no issue. Believe you me Alj ... if I find diamonds rounded in such a way that ...

a. would cause a diamond to improperly fall out of of the Ex zone or
b. cause a diamond to suffer optically because of rounding

I will be the first one to report it and demonstrate it with the data. At this point however you are only using a hypothetical situation that has not been confirmed. BTW if any of my other peers have found such an instance, I''d be very interested to see.

Devil''s advocate for a moment, though. Assume for a moment that what you claim is so....that no one will see a difference from rounding. Million dollar question: then why do it? Why round at all? Your argument is that 34.7 is just as good as 34.9.

Actually 34.7 would be rounded to 34.5 (unless it''s =>34.75) and 34.9 would be rounded to 35. I understand ya though.

If so, why not just report the 34.7 measured and leave it at that? What is the purpose of changing the number if it won''t make any difference---improvement OR detraction, as you claim? It takes an extra step to measure something and THEN make an adjustment (which you claim makes no visual difference). Doing something--especially making an additional step---just for the sake of doing it makes no sense. If there weren''t some advantage to SOMEONE, there would have been no reason to do it.

I agree! In my prior post Alj, I specifically stated... "Let me make one thing clear ... I am for as much detail as possible." This is why I prefer the measurements given on the AGS Report. They are only rounded within 1/100th of a degree.

In fact I wrote to GIA and expressed my feelings that it was a mistake to not include upper girdle and lower girdle angles in the FacetWare. Since I''ve had the ability to measure each facet set I realize how a knowledge of all the facets (especially including upper/lower girdle angle facet measurements) impact performance (and also a cut grade!).

How does rounding potentially benefit the consumer? I can''t think of a single way that consumers would benefit from the practice of rounding, other than false sense of thinking that their stones are more elite than they really are. (In the absolute best case scenario, there is no difference and they don''t lose anything....but nor do they benefit.)

That all depends on how you want to define "elite" and who you are talking to. If you''re asking me, neither lab is really accounting for what I would classify as "elite". Elite to me is ideal slope and azimuth angles coupled with superior optical symmetry (on top of the rest of the characteristics the labs look at) which can be demonstrated both with optical results (DiamXray, Bscope, Isee2) combined with the numberes on a Helium scan for confirmation. Neither GIA or AGS look at azimuth angles (and how far they deviate from ideal), nor do they look at optical symmetry or the minutae of detail under a reflector that meets the definition of elite in my book.

The *key* here is understanding how each of these labs define what they consider to be elite. In GIA''s case, their elite are stones which consistently were selected by their observers as displaying the highest optical characteristics of brightness, fire and scintillation as well as the metrics of weight ratio, durability, polish and symmetry. Light performance grading with GIA is not based on any single technology except that of the human eyes and what the observers in their study found to be the most appealing.

How does GIA potentially benefit from rounding? I can think of a few possibilities:

1) it makes it much harder for consumers to compare apples to apples when considering both GIA and AGS stones. That difficulty and confusion certainly would potentially benefit GIA since they are the more widely known lab. If a customer cannot definitively determine which side is more accurate, the default will always benefit the more widely known (GIA in this case).

While I would certainly prefer the more detailed information, for those of us on the front lines here the data provided on the GIA Report is definitely sufficient to help determine an accurate *appearance* for those who know how to interpret numerical data to face up appearance. Even if you took the more exacting measurements on an AGS Report (or even better a Helium) and plugged them into say DiamCalc there is no world of difference that would benefit either lab. In fact, the educated consumer who prefers more exacting detail (even if its not visible) I would think would prefer the AGS stone and not the GIA stone (unless the GIA stone is perhaps accompanied with a more detailed Sarin/OGI/Helium Report). As a professional in this industry who works with these technologies on a daily basis I don''t see GIA or AGS benefitting either way. The consumer who is educated on these issues and takes the time to learn will realize that the minutae of rounding on a GIA Report will be no difference in optical performance than an AGS stone with reported 34.7 crown angles and 40.9 pavilion angles.

2) I suspect that rounding means that stones that would otherwise miss the ''GIA ex'' mark would then qualify. With this as an incentive to dealers, it certainly makes dealers want to put more marginal stones through GIA because there is greater chance of getting the EX grading and the associated $$ premium.

Again ... this is presuming that MOST cutters shooting for hte Ex grade will cut their stones on the cusp and I''m sure there is a large share of those out there (as there were with AGS prior system). This may in fact be true but I can''t speak for all those cutting houses as a whole because I know the cutters who I do biz with don''t do that. The question the consumer needs to ask themselves at that point is ... "If the GIA EX I am looking at falls on the cusp (and the nice people here will be certain to do so I am sure), does this diamond indeed *speak to them* as they view it alongside others? My consistent counsel to folks is to *look and see and compare* for themselves and pick what appeals most to their eyes. I''ve yet to see the stones that fall on the steep/deep cusp of GIA''s Ex grade so I will not comment. I am presuming it will have an appearance that I would not personally prefer but to make any statement for or against would be premature at this point in time. On point #2 I understand where you''re coming from and at this point, these stones on the cusp do concern me as well. Frankly I can''t wait to get one so I can perform my own tests and observations with it.

Why do they choose to round? What does it accomplish that measured data doesn''t? I''ve yet to hear any reasonable explanation for it. I fail to see one possible advantage to the customer by adopting this practice.....

I''m really hoping that other experts who support the GIA rounding position will chime in to offer some insights on this.

Me too. I''d like to see examples where ...

A. Sarin''s that don''t agree, cause a stone to get a VG grade instead of an Ex grade that should have fallen one way or the other.
B. The rounding impacts face up appearance to the point that would cause the diamond to decrease in brightness yet maintain a GIA Ex grade.

Overall ... I really enjoy the dialogue dear.

In case you''re wondering Alj, there is no chip on my shoulder either.

My stance on this is what you might consider balanced. At least I do. I am for more detail (more than what is currentlly provided on both GIA and AGS Reports) and in this case we are in agreement. Personally I''d like to see variances and upper girdle angles included.

At the same time, I don''t see this rounding as the issue that it is being blown up to be. If someone, anyone can provide real instances where the rounding impacts face up appearance in a negative manner, or in such a way as to cause a stone to receive the VG grade when it should have received Ex then the rounding can be viewed as being a very practical move on behalf of GIA as the minutae of rounding as far as I''ve been able to determine doesn''t impact performance one bit.

Kind regards,

 

[Garry H (Cut Nut)]

Date: 8/15/2006 5:03:13 PM
Author: Rhino
Hi Ira,

I think it best for me to answer via Alj''s response since it appears I missed it in the other thread. My comments will be in bold.


When you have a cut grading system based on observation testing and face up appearance and you''ve been in this trade for as long as I have you get to know that when it comes to face up appearance ... (and I''m talking on a practical level now), if you put a diamond with 34.68 crown angles next to a diamond with 34.3 crown angles you will not see a difference. If we take 2 diamonds and both have 41 degree pavilion angles, and I lay a stone with 34.8 or 35.2 crown angles side by side to it ... guess who''ll be able to see the difference? Answer: Nobody.

GIA Crown 35 pav 41
can be 35.24 -41.09
or 34.76 - 40.91

I know which I would prefer - and I think you would be able to tell the difference too Rhino.

Ira your example was very good

 

[aljdewey]

Date: 8/16/2006 5:14:00 PM
Author: Garry H (Cut Nut)

GIA Crown 35 pav 41
can be 35.24 -41.09
or 34.76 - 40.91

I know which I would prefer - and I think you would be able to tell the difference too Rhino.

Amazing.....I think so too, Garry.