AGS introduces cut grading on DQR reports

[Serg]

Date: 11/4/2008 10:26:08 AM
Author: adamasgem

Date: 11/4/2008 9:06:57 AM
Author: Serg

Dark Black line is boundary PGS 0

What is misleading in your comparison is that you continually fail to mention that the Dark Black line is a boundary where there is a only a POSSIBILITY of getting a 0, in the real world, but not a GUARANTEE, because it is based entirely on PERFECT symmetry, which doesn't exist, and you don't know the gradients or probabilities of getting that ellusive 0.

In fact at the boundarys of the grade, you ought to look at the sensitivity of scanning errors (variances) by running PGS with multiple scans, and not only presenting the quantized results.. remember 0.49 is a 0 and 0.51 is a 1.0

You are not telling the complete picture Sergey.

If you analyse the stone completely, you may or may not get a better grade

And besides the criteria are different, and it would take 17 times as long to make all the runs to do the equivilant processing on the actual stone (PGS) , and no one in the TRADE wants to pay for that extra time.

'Cheaper, Faster, Better' is a Mantra of the TRADE (and maybe some of the buying public), as it was for ill fated NASA management. The trade seems to want decisions from the labs (or tools) that could mean 10's of thousands of dollars (typically thosands) made in little or no time, which results in work with less confidence in the work product.

Real stupid on the trades part, in my opinion.

How many times should I say it in this thread ????
How many ???



see for example

"P: 10/18/2008 3:21:04 AM

Serg

Ideal Rock
Total Posts: 1,190
Last Post: 11/4/2008
Member Since: 3/22/2002

Marty,



Symmetry is not issue at all.
I compare “ Absolute symmetry ” diamond with “ Absolute symmetry ” diamond ( apple with apple)

Of course PGS 0 result is not GARANTY for cutters, because symmetry , polish, and other issues could be not enough for ASG Platinum 0 grade . ( same for AGS gold grading system. Set of parameters is not enough for final grade)

Please do not start this argue again. We do not compare apple and orange.

Our point what if SAME REAL polished diamond could receive AGS GOLD VG grade and AGS Platinum 0 grade is very Misleading for market.

It is even more misleading than GIA excellent grade and AGS 4 grade for same real polished diamond( all we were agree early what such contradictory grade systems are not good for consumer confidence )
Now situation even worse, because contradictory grades could come from one Lab( papers are different of course , but both these papers have same Consumer BRAND)


Sergey Sivovolenko
CEO OctoNus

"

 

[Serg]

Marty,

re:
What is misleading in your comparison is that you continually fail to mention that the Dark Black line is a boundary where there is a only a POSSIBILITY of getting a 0, in the real world, but not a GUARANTEE, because it is based entirely on PERFECT symmetry, which doesn't exist, and you don't know the gradients or probabilities of getting that ellusive 0.

Do you know what ASG Gold is not GUARANTEE grade too.
Scanner can not do grade, due SAME symmetry issue

Do you know it??

 

[Serg]

Marty,

re:What is misleading in your comparison is that you continually fail to mention that the Dark Black line is a boundary where there is a only a POSSIBILITY of getting a 0

AGS GOLD Ideal zone on Charts is also ONLY a POSSIBILITY to receive Ideal grade.

I compare apple and apple.

Please stop publish misleading Information about my work. If you have not enough understanding it is not mean what I publish false information.

 

[Serg]

Marty,

Please try think about AGS motivation to give Ideal grade for diamonds with Ideal AND Excellent polish and symmetry

Excellent is not Top ASG grade for symmetry at all.

It COULD BE more difficult to cut ASG GOLD IDEAL with Ideal polish and Symmetry than AGS Platinum 0.

It is Hypothesis only because I do not know ASG rules for Symmetry in digital( objective) format. I am afraid nobody know it .

At least I do not know any reason Why is more difficult to Cut AGS Platinum 0 than AGS GOLD Ideal with Ideal symmetry and polish grade. why??

Could anybody give me detail explanation?

 

[adamasgem]

Date: 11/4/2008 10:57:43 AM
Author: Serg

Marty,

re:What is misleading in your comparison is that you continually fail to mention that the Dark Black line is a boundary where there is a only a POSSIBILITY of getting a 0

AGS GOLD Ideal zone on Charts is also ONLY a POSSIBILITY to receive Ideal grade.

I compare apple and apple.

Please stop publish misleading Information about my work. If you have not enough understanding it is not mean what I publish false information.

Seregy, with all due respect, you are comparing a much less than 100% Probability event (Platinum Boundaries) with a 100% Probability event (Gold). The Perfect symmetry case may be a 0% Probability event, in reality.

 

[Serg]

Date: 11/4/2008 11:30:28 AM
Author: adamasgem

Date: 11/4/2008 10:57:43 AM
Author: Serg



Marty,

re:What is misleading in your comparison is that you continually fail to mention that the Dark Black line is a boundary where there is a only a POSSIBILITY of getting a 0

AGS GOLD Ideal zone on Charts is also ONLY a POSSIBILITY to receive Ideal grade.

I compare apple and apple.

Please stop publish misleading Information about my work. If you have not enough understanding it is not mean what I publish false information.

Seregy, with all due respect, you are comparing a much less than 100% Probability event (Platinum Boundaries) with a 100% Probability event (Gold). The Perfect symmetry case may be a 0% Probability event, in reality.

re:The Perfect symmetry case may be a 0% Probability event, in reality.

Marty, it could be very surprised for you What PGS software is not very sensitive to symmetry deviations

please see example. this stone is far from perfect symmetry.

Will PGS downgrade this diamond???

I am very Sorry, But your are too far from real world

You do not know what :

1) PGS is not very sensitive to asymmetry( Btw it is not critic . LR is not sentsitive for symmetry deviations. it is just fact )
2) AGS GOLD Ideal zone on Charts is also ONLY a POSSIBILITY to receive Ideal grade.

please fix your map.
please account real facts about cut grading systems

 

[adamasgem]

Date: 11/4/2008 11:18:51 AM
Author: Serg

It is Hypothesis only because I do not know ASG rules for Symmetry in digital( objective) format. I am afraid nobody know it .

Could anybody give me detail explanation?

Sergey, As far as I know, there are NO established digital rules, and that I think might be forthcoming, it is a lot of work.

I have privately suggested some extensive data correlations, to see establish the distributionsal assymetry statistics of the factors (T,CA, PA etc) versus the graders somewhat subjective "calls" of "Ideal", "Ex", "VG" etc..

But, as you know, the statistics inthemselves don''t tell the complete story, for example you can (approximately) measure physical symmetry, but you have to visualize and/or compute optical symmetry (which is still subject to the statistics of the measurement errors), So you might want to look at the stats in opposing ways, as to importance, like the stats of the difference between the crown angle and the opposing pavillion main, might be more revealing as to establishing digital standards. Of course these digital (objective) standards should probably be with respect to the measurement uncertainty to establish statistcal significance.

I''ve looked at that aspect, and it can be "very" important at the boundaries, by "very" , it can tilt the "call" a grade, like 0.49 vs 0.50 boundary (0 or 1), the same problem all numeric systems have.

I have lobbyed for some estimate of the grade uncertainty be included in the reports I believe that the computed unrounded values be are available on the reports, like it is in the PGS software.

 

[Serg]

Date: 11/4/2008 11:53:50 AM
Author: adamasgem

Date: 11/4/2008 11:18:51 AM
Author: Serg

It is Hypothesis only because I do not know ASG rules for Symmetry in digital( objective) format. I am afraid nobody know it .

Could anybody give me detail explanation?

Sergey, As far as I know, there are NO established digital rules, and that I think might be forthcoming, it is a lot of work.

I have privately suggested some extensive data correlations, to see establish the distributionsal assymetry statistics of the factors (T,CA, PA etc) versus the graders somewhat subjective ''calls'' of ''Ideal'', ''Ex'', ''VG'' etc..

But, as you know, the statistics inthemselves don''t tell the complete story, for example you can (approximately) measure physical symmetry, but you have to visualize and/or compute optical symmetry (which is still subject to the statistics of the measurement errors), So you might want to look at the stats in opposing ways, as to importance, like the stats of the difference between the crown angle and the opposing pavillion main, might be more revealing as to establishing digital standards. Of course these digital (objective) standards should probably be with respect to the measurement uncertainty to establish statistcal significance.

I''ve looked at that aspect, and it can be ''very'' important at the boundaries, by ''very'' , it can tilt the ''call'' a grade, like 0.49 vs 0.50 boundary (0 or 1), the same problem all numeric systems have.

I have lobbyed for some estimate of the grade uncertainty be included in the reports I believe that the computed unrounded values be are available on the reports, like it is in the PGS software.

Marty,
could you please confirm what YOU do not know any reason:

Why AGS Platinum 0 is more difficult to cut than AGS GOLD Ideal with Ideal symmetry and polish grade.
?

I think such reasons are absent.

 

[adamasgem]

Date: 11/4/2008 10:44:50 AM
Author: Serg

Marty,

re:
What is misleading in your comparison is that you continually fail to mention that the Dark Black line is a boundary where there is a only a POSSIBILITY of getting a 0, in the real world, but not a GUARANTEE, because it is based entirely on PERFECT symmetry, which doesn''t exist, and you don''t know the gradients or probabilities of getting that ellusive 0.

Do you know what ASG Gold is not GUARANTEE grade too.
Scanner can not do grade, due SAME symmetry issue


Do you know it??

I completely understand the issue between the correlation of the "subjective" symmetry grade and the "objective" measurement statistics, see my previous posts..

You as an equipment producer, can give repeatability statistics by using the same stone multiple times, and getting a limited set of observational data.

The Labs, through their extensive databases should eventually set up queries that look at the stats of "subjective grade" of whole values of particular angles or measurements, both as a quality control check, and to establish digital standards that are of most importance.

I think we are on the same page here.

 

[strmrdr]

Date: 11/4/2008 11:58:21 AM
Author: Serg
could you please confirm what YOU do not know any reason:


Why AGS Platinum 0 is more difficult to cut than AGS GOLD Ideal with Ideal symmetry and polish grade.

?


I think such reasons are absent.

1: averages can hide a lot of sins that the Plat catches.
One example would be what Todd used to call phony ideals which had wide ranging pavilion angles but the average was just good enough to get the grade on the steep end of the grade but the majority of the facets were over the grade limit.
So having to keep better control over the pavilion and less room to recover from mistakes is one.

 

[Serg]

Date: 11/4/2008 12:13:59 PM
Author: strmrdr

Date: 11/4/2008 11:58:21 AM
Author: Serg
could you please confirm what YOU do not know any reason:


Why AGS Platinum 0 is more difficult to cut than AGS GOLD Ideal with Ideal symmetry and polish grade.

?


I think such reasons are absent.

1: averages can hide a lot of sins that the Plat catches.
One example would be what Todd used to call phony ideals which had wide ranging pavilion angles but the average was just good enough to get the grade on the steep end of the grade but the majority of the facets were over the grade limit.

Karl,


Did you see my example? Do you think PGS LR results strongly depends from culet shift or even girdle deviation?
Labs downgrade such diamonds by Symmetry deviations!
Minor symmetry deviations will reduce grade , but minor symmetry deviations are not change PGS results( except case when diamond on boundary. This case in not important for other reasons).

You overestimate possibility of PGS. Unfortunately LR metrics can not be sensitive to symmetry deviations at least for RBC

 

[strmrdr]

Date: 11/4/2008 12:29:05 PM
Author: Serg

Minor symmetry deviations will reduce grade , but minor symmetry deviations are not change PGS results( except case when diamond on boundary. This case in not important for other reasons).

That is exactly the stones I''m talking about those on the edges.
These stones got id/id sym/polish.
Why isn''t boundary cases important?
Cutters try and push the steep/deep end of cut grades all the time.

 

[Serg]

Date: 11/4/2008 12:35:26 PM
Author: strmrdr

Date: 11/4/2008 12:29:05 PM
Author: Serg


Minor symmetry deviations will reduce grade , but minor symmetry deviations are not change PGS results( except case when diamond on boundary. This case in not important for other reasons).

That is exactly the stones I''m talking about those on the edges.
These stones got id/id sym/polish.
Why isn''t boundary cases important?
Cutters try and push the steep/deep end of cut grades all the time.

Please send link to this stone

 

[strmrdr]

I used to have a few sarin files for them.
I will see if I can find them they are on a CD around here someplace.

I would be interested in the PGS grade of this one that ranges to the shallow side and should get Gold Ideal.

 

[Serg]

Date: 11/4/2008 12:54:23 PM
Author: strmrdr
I used to have a few sarin files for them.
I will see if I can find them they are on a CD around here someplace.

I would be interested in the PGS grade of this one that ranges to the shallow side and should get Gold Ideal.

I can not download . Please check.

re:These stones got id/id sym/polish.

did this stone get ASG patinum id/id sym/polish.?? Please clarify

 

[strmrdr]

Date: 11/4/2008 12:59:06 PM
Author: Serg

Date: 11/4/2008 12:54:23 PM

Author: strmrdr

I used to have a few sarin files for them.

I will see if I can find them they are on a CD around here someplace.


I would be interested in the PGS grade of this one that ranges to the shallow side and should get Gold Ideal.

I can not download . Please check.


re:These stones got id/id sym/polish.



did this stone get ASG patinum id/id sym/polish.?? Please clarify

Not sure if this particular one did.
retrying upload...

.srn file download is broke for some reason am notifying Andrey.

 

[strmrdr]

trying dmc

ok dmc worked.
I will look for the others once I get some sleep.

 

[Serg]

Date: 11/4/2008 1:02:00 PM
Author: strmrdr

Date: 11/4/2008 12:59:06 PM
Author: Serg

Date: 11/4/2008 12:54:23 PM

Author: strmrdr

I used to have a few sarin files for them.

I will see if I can find them they are on a CD around here someplace.


I would be interested in the PGS grade of this one that ranges to the shallow side and should get Gold Ideal.

I can not download . Please check.


re:These stones got id/id sym/polish.



did this stone get ASG patinum id/id sym/polish.?? Please clarify

Not sure if this particular one did.
retrying upload...

.srn file download is broke for some reason am notifying Andrey.

Karl,

I will spend my time only if diamond has

1) ASG platinum grade ( AGS PGS 1 or worse)
2) ASG ideal symmetry
3) Average proportions suitable for ASG0

And you have good 3d model

 

[strmrdr]

Serg, fair enough I will see what I can find.

 

[Regular Guy]

me me me me...

ahem (clearing throat)...

three points...(or maybe just one)...


1) have I been understanding this conversation to morph into a deepening exploration of the meaning of Measurement Error?

2) Relatedly...at least...with gold...you are including less points being measured. Right? Presuming if so...we are still...if only by redefining that this is being what is being talked about...still asking the same question, but in a different way. Right? Which is how much more off can gold be from platinum, in terms of understanding with sufficient confidence what you have, in terms of how well it performs.

3) Thanks for the caffeine burst gentlemen. I''m taking lunch. If you want to amplify it further...when you vote, you can get a free cup from Starbucks...or so I''ve heard on SNL, I think. Apologies if my earlier post got this unpinned. This is a free board, right?

Warm regards,

P.S If I am right....and me is much of what this conversation...at least recently has been about...is it clear that me is like most of what this is all about?

 

[Serg]

Date: 11/4/2008 2:13:12 PM
Author: Regular Guy
me me me me...

ahem (clearing throat)...

three points...(or maybe just one)...


1) have I been understanding this conversation to morph into a deepening exploration of the meaning of Measurement Error?

2) Relatedly...at least...with gold...you are including less points being measured. Right? Presuming if so...we are still...if only by redefining that this is being what is being talked about...still asking the same question, but in a different way. Right? Which is how much more off can gold be from platinum, in terms of understanding with sufficient confidence what you have, in terms of how well it performs.

3) Thanks for the caffeine burst gentlemen. I'm taking lunch. If you want to amplify it further...when you vote, you can get a free cup from Starbucks...or so I've heard on SNL, I think. Apologies if my earlier post got this unpinned. This is a free board, right?

Warm regards,

P.S If I am right....and me is much of what this conversation...at least recently has been about...is it clear that me is like most of what this is all about?

re:1) have I been understanding this conversation to morph into a deepening exploration of the meaning of Measurement Error?

No.
Measurement Errors are irrelevant for main discussion here because all agree( I hope) what Measurement Errors are relevant ( critical on same level) for all cut grading systems

 

[beryl]

Sergey:

Thanks for your comments.
This thread looks interesting but I must read and understand it before I can comment meaningfully.
I hope to be able to have some good discussions with you.

Garry:

You were touting the 5:1 ratio long before Moscow; people laughed at you because of it. Remember?
Although I showed in 1975 that historically ''best'' cuts for all gemstones are on the edge of the head obscuration zone, I didn''t know why. You came up with the answer in 2000. We did a good thing together.
In yardening, crisp borders are effective. People compliment my gardens even when there are no flowers, and perhaps they don''t know why. This is analogous to sharp edges on facets which make sharp contrast that is dited as appealing.

 

[Garry H (Cut Nut)]

Date: 11/4/2008 5:56:29 PM
Author: beryl
Sergey:

Thanks for your comments.
This thread looks interesting but I must read and understand it before I can comment meaningfully.
I hope to be able to have some good discussions with you.

Garry:

You were touting the 5:1 ratio long before Moscow; people laughed at you because of it. Remember?
Although I showed in 1975 that historically ''best'' cuts for all gemstones are on the edge of the head obscuration zone, I didn''t know why. You came up with the answer in 2000. We did a good thing together.
In yardening, crisp borders are effective. People compliment my gardens even when there are no flowers, and perhaps they don''t know why. This is analogous to sharp edges on facets which make sharp contrast that is dited as appealing. typo - diting = citing?

Sergey has on a seperate communication suggested that part of the widely held appeal of Hearts and Arrows stones could be simply that the equipment used is better at producing ultra flat facets. I think you might agree Beryl?

 

[michaelgem]

(To focus attention on some issues, which are quickly overshadowed, here are a couple with slight rewording as I read it)

It could be a very big surprise for many that PGS software is not very sensitive to symmetry deviations

1.) PGS is not very sensitive to asymmetry( Btw this is not a criticism. LR is not sensitive to symmetry deviations. It is just a fact )
2.) Same as in the AGS PLATINUM grading, AGS GOLD Ideal zone on Charts is also ONLY a POSSIBILITY to receive Ideal grade.
Do you know that ASG Platinum is not a GUARANTEE of the grade?
Do you know that ASG Gold is not a GUARANTEE of the grade too?
Also, scanners can not guarantee the grade, due to the SAME symmetry issue

Sergey Sivovolenko

(Near the borders, scanning errors can give incorrect grades as well as rounding errors. MDC)

Those that believe the H&A, optically symmetric, Tolkowsky Ideal (40.75, 34.5) is the “pinnacle of light performance” may equally disagree with either the Platinum or Gold Ideal, because both grading systems will give the same Ideal grade to a diamond without H&A symmetry. (Sergey''s 1.)

Those who have expressed the belief that 40.75 is the best pavilion angle, and there is a wall at 41 degrees, may also disagree with both systems equally. Both give the Ideal grade to diamonds cut to (41.5, 32), (which importantly gives a better weight yield from typical rough.)

Michael D. Cowing

 

[michaelgem]

Just a note from a quick look at Sergey''s charts.

The inverse slope or “Ideal axis” for the Platinum 0, that AGS reports as -5:1, appears to be closer to the approximate -4.5:1 that I reported in the Accordance article in the Journal . http://www.acagemlab.com/news/JoG07305.pdf

Also notice that the same cursory look puts the axis of the Gold Ideal between -4:1 and -4.5:1 and closer to -4:1.

Ahhhh Yes. That stirs up nostalgic memories of epic discussions of yesteryear.

Michael D. Cowing

 

[beryl]

Date: 11/4/2008 6:42:43 PM
Author: Garry H (Cut Nut)

Date: 11/4/2008 5:56:29 PM
Author: beryl
Sergey:

Thanks for your comments.
This thread looks interesting but I must read and understand it before I can comment meaningfully.
I hope to be able to have some good discussions with you.

Garry:

You were touting the 5:1 ratio long before Moscow; people laughed at you because of it. Remember?
Although I showed in 1975 that historically 'best' cuts for all gemstones are on the edge of the head obscuration zone, I didn't know why. You came up with the answer in 2000. We did a good thing together.
In yardening, crisp borders are effective. People compliment my gardens even when there are no flowers, and perhaps they don't know why. This is analogous to sharp edges on facets which make sharp contrast that is dited as appealing. typo - diting = citing?

Sergey has on a seperate communication suggested that part of the widely held appeal of Hearts and Arrows stones could be simply that the equipment used is better at producing ultra flat facets. I think you might agree Beryl?

Garry:
Sorry for typo: 'cited' is correct.
Flatness of facets is vital to snappy on-off reflections and sharpness of edges intensifies this. Convex facets and rounded edges are a major problem in colored-stone cutting, due to equipment & operator; I have not seen it in diamonds, but would expect it on fast-cut cheap diamonds.
On the present subject, recall my presentation in Moscow - that CUT grading should consist of 2 parts - one for PROPORTIONS, the other for MAKE (symmetry, polish, etc). This distinction seems missing in some discussions here. PROPORTION can be graded numerically, once a chart is established, but MAKE is subjective; therefore a combined grade is subjective, and so you will often get a different COMBINED grade from different appraisers. The two factors should be cited separately.
Pardon my ignorance: what is 'PGS software'? (Paul Slegers?)

 

[Serg]

Date: 11/5/2008 3:06:53 AM
Author: beryl

Date: 11/4/2008 6:42:43 PM
Author: Garry H (Cut Nut)

Date: 11/4/2008 5:56:29 PM
Author: beryl
Sergey:

Thanks for your comments.
This thread looks interesting but I must read and understand it before I can comment meaningfully.
I hope to be able to have some good discussions with you.

Garry:

You were touting the 5:1 ratio long before Moscow; people laughed at you because of it. Remember?
Although I showed in 1975 that historically ''best'' cuts for all gemstones are on the edge of the head obscuration zone, I didn''t know why. You came up with the answer in 2000. We did a good thing together.
In yardening, crisp borders are effective. People compliment my gardens even when there are no flowers, and perhaps they don''t know why. This is analogous to sharp edges on facets which make sharp contrast that is dited as appealing. typo - diting = citing?

Sergey has on a seperate communication suggested that part of the widely held appeal of Hearts and Arrows stones could be simply that the equipment used is better at producing ultra flat facets. I think you might agree Beryl?

Garry:
Sorry for typo: ''cited'' is correct.
Flatness of facets is vital to snappy on-off reflections and sharpness of edges intensifies this. Convex facets and rounded edges are a major problem in colored-stone cutting, due to equipment & operator; I have not seen it in diamonds, but would expect it on fast-cut cheap diamonds.
On the present subject, recall my presentation in Moscow - that CUT grading should consist of 2 parts - one for PROPORTIONS, the other for MAKE (symmetry, polish, etc). This distinction seems missing in some discussions here. PROPORTION can be graded numerically, once a chart is established, but MAKE is subjective; therefore a combined grade is subjective, and so you will often get a different COMBINED grade from different appraisers. The two factors should be cited separately.
Pardon my ignorance: what is ''PGS software''? (Paul Slegers?)

Beryl ,

If we speak about cut grade only :

I prefer systemize methodic according external goals :
1) Light performance grade
2) Cutter Craft

Because Flatness of facets is critical for brightness we need grade Flatness in “Light performance “ part. Even small convexity( 3 microns for 100-300 micron facets is more a less typical convexity for good diamond cut) produce big astigmatism , what significantly reduce brightness for flashes .

Fancy cuts need better facet flatness because a lot of ray reflections accumulate astigmatism .

Cutter Craft mainly is symmetry issue + may be smoothness

Milkyness( transparency ) is could be part Light performance grade ( cut is just one part light performance)

PGS – is ASG software for cut light performance grade( with weight deduction) based on 3D model

 

[adamasgem]

Date: 11/5/2008 4:39:10 AM
Author: Serg



Because Flatness of facets is critical for brightness we need grade Flatness in “Light performance “ part. Even small convexity( 3 microns for 100-300 micron facets is more a less typical convexity for good diamond cut) produce big astigmatism , what significantly reduce brightness for flashes .

Fancy cuts need better facet flatness because a lot of ray reflections accumulate astigmatism .

Cutter Craft mainly is symmetry issue + may be smoothness

Sergey. Are you talking Roughness (as in a matte finish versus polished) or Flatness (as in concave or convex) ?

 

[Serg]

Date: 11/5/2008 8:50:58 AM
Author: adamasgem

Date: 11/5/2008 4:39:10 AM
Author: Serg





Because Flatness of facets is critical for brightness we need grade Flatness in “Light performance “ part. Even small convexity( 3 microns for 100-300 micron facets is more a less typical convexity for good diamond cut) produce big astigmatism , what significantly reduce brightness for flashes .

Fancy cuts need better facet flatness because a lot of ray reflections accumulate astigmatism .

Cutter Craft mainly is symmetry issue + may be smoothness

Sergey. Are you talking Roughness (as in a matte finish versus polished) or Flatness (as in concave or convex) ?

Marty,
Both

smoothness or Roughness

AND

Flatness( convex). Flatness is more critical for Brightness.

Labs grade only smoothness( Roughness )

 

[diagem]

Date: 11/5/2008 8:57:55 AM
Author: Serg

Date: 11/5/2008 8:50:58 AM
Author: adamasgem

Date: 11/5/2008 4:39:10 AM
Author: Serg






Because Flatness of facets is critical for brightness we need grade Flatness in “Light performance “ part. Even small convexity( 3 microns for 100-300 micron facets is more a less typical convexity for good diamond cut) produce big astigmatism , what significantly reduce brightness for flashes .

Fancy cuts need better facet flatness because a lot of ray reflections accumulate astigmatism .

Cutter Craft mainly is symmetry issue + may be smoothness

Sergey. Are you talking Roughness (as in a matte finish versus polished) or Flatness (as in concave or convex) ?

Marty,
Both

smoothness or Roughness

AND

Flatness( convex). Flatness is more critical for Brightness.

Labs grade only smoothness( Roughness )

Serg..., do you know of any Dia scans that can detect convex facets?