Diamond Buying by the Numbers - Perspective.

[diagem]

Date: 4/21/2010 3:13:21 PM
Author: Karl_K

Date: 4/21/2010 1:36:32 PM
Author: oldminer
Thanks for the advisory. Seems interesting, at least to me, that the symmetry we can measure objectively may have a noticeable range before the symmetry grade is lowered to the Very Good step. As a follow-up,. Are there a range of crown angles from high to low which would lower always the Symmetry grade from Ex to VG? Such grade setting points always are of interest although not the way anyone would suggest to select a diamond.

At some point it becomes physically impossible to line them up at the ex level that varies by facet, is there a downgrade before that point?

From my rather short experience in this cutting arena I dont think there is a clear border that differentiate between X & VG.

its a combination of numerous factors...

For example, take Todd Gray''s comment above

"what if the flow of the facets went something like 34.5 | 34.9 | 34.8 | 34.7 | 34.9 | 34.8 | 34.7 | 34.9 | it might be something you would want to take into consideration?"

And then combining the following Pav angles in correlation: "40.4 | 40.7 | 40.8 | 40.9 | 40.8 | 40.7 | 40.9 | 41.0 |"


I didnt test it..., but in such case (I believe) due to the nature of the overall precision cut other parameters would move out of sync of the overall excellent symmetry level required, like culet/table (tilt) off-center or a wide range of girdle thickness that would automatically display the "above mentioned "border".

Many more examples are available depending on facet designs.

On a side note to all involved in this discusion..., please take into consideration that scan error stands at 3-4 tenths of a degree (AND NOT ALWAYS AT THE SAME POSITION

).

 

[ChunkyCushionLover]

It is commonly and correctly

Only with with the appropriate pavillion angle.

See here and check the fire maps from Sasian et al.

"The fire matrices show that the old diamond-cutting industry
rule of increasing the crown angle to achieve more
fire is not necessarily true. It only significantly applies to
stones at or near the main cutter’s line or about lines passing
by other regions such as the left-bottom and top-right
corners."

I am not in a knowledgeable enough position to question the fundamental validity of this statement but it is a correct conclusion based on the observation of the fire(dispersion) matrices.

 

[Paul-Antwerp]

Date: 4/21/2010 12:56:16 PM
Author: Regular Guy

Date: 4/21/2010 6:26:31 AM
Author: Paul-Antwerp
The AGS Fire-metric is a part of their cut-grade, I do not know for how much it counts.

The metric measures potential fire of a stone, just like the ASET-system does for potential brightness. The metric itself is a complicated combination of reverse and forward ray-tracing.

I must say that I already saw the fire-metric explained two years ago, but only in last week''s AGS-presentation did I understand it. I am still struggling with all the consequences, but it seems to prove a lot of views that I already held intuitively.

Live long,

I suppose two data points of particular interest, from these comments, are both first & second hand from your observations.

Truly, it would be good to hear as first hand as possible how AGS measures fire.

However, as both our reporter in the field, and the person now bringing forward these observations/reflections, I (and maybe we?) would be interested in your personal thoughts on this, Paul.

For example, you HAVE been singularly (well, Rhino has been broadly critical, too, without providing the more detailed comments you have done) critical of the HCA''s intent to say anything purposive about fire and scintillation. Clearly, you here are supportive of AGS''s analysis.

I just went to Garry''s HCA site to see more of what he says about fire in particular. Octonus seems to be implicated...and although the material at this site (from Garry) is dated, and Octonus is in motion, I don''t know the extent to which any fundamentals on fire have been recalculated by Octonus or not. Consistent with Garry''s comments at his site, and with the HCA, are the idea that both crown height, and table size bring significant effects. It would be interesting to know what variance there is between these two analyses, at least from your point of view, if not from AGS.

I copy below what seems to be the pertinent info from Garry''s HCA site:

----------

It is commonly and correctly believed that diamonds with steeper crown angles and smaller tables have enhanced fire. Believing this makes objective observation based study of the nature undertaken here was somewhat difficult. However the discovery that shallow crown angled diamonds display enhanced fire challenged the preconditioning notion.

I acknowledge that fire is the most subjective and least reproducible of the four factors presented here. Never the less we have made many loosely structured comparisons with actual diamonds in various lighting conditions and a variety of observers.

The first of these two sets of charts show a selection of crown and pavilion proportion combinations with the virtual fire tool from the MSU / Octonus website www.cutstudy.com/cut/english/comp/scint1.htm. The second chart has had a head shadow effect subtracted.

Because HCA is concerned with the face up view, removal of the central section of the image effectively reproduces the potential for fire should a ray of light fall on the diamond from the same direction as one of these areas of a firey flash. Many people find this concept rather difficult to understand, and it is very difficult to explain. It may help to imagine that we are considering the ray of light to be going in the opposite direction. Therefore the more firey flashes on the imaginary screen, the more potential fire could be displayed. However we must always remember that excessive brilliance will drown out potential fire.

Ira,

I still need to digest the Fire-information more in detail, before I can try to explain it. Iiro gave it a preliminary shot in this thread, but it got snowed under by pre-conceptions and gradually went off-topic.

Thank you for identifying me however as being critical about the HCA-assessment of fire and scintillation. I indeed find it difficult to accept that the HCA bases a fire-scintillation on a pre-conception of the industry (based upon one single aspect of proportions), while the basis of the HCA itself in its assessment of brightness is undermining the old preconceptions of the industry. In other words, if the HCA is built upon the fact that all proportions need to work together to achieve a result, how can it rely mainly on one proportion when judging fire?

Let us agree that the HCA is a great rejection-tool, assessing potential brightness.

Live long,

 

[Paul-Antwerp]

Date: 4/21/2010 4:51:25 PM
Author: ChunkyCushionLover

Great thread Todd, got me thinking a bit about rounds and interpreting images again.

Couple of points:

1) The methodology used for grading disperion(there is no fire metric) in the AGS/PGS system and its foundations are found in this paper I didn''t purchase the PGS software or its supporting documentation so I don''t have the specific grading information. I would be interested to know specifically a lot of the fine details of the calculation for dispersion from those fire maps. Specifically for all the light performance categories I am interested to know how they weight each of the images. I read some time ago faceup was most heavily weighted then -5 degrees on each side is worth less, -10 on each side even less. I hope someone wouldn''t mind posting some of this for a lot of the catergories of PGS grading like Brightness and Dispersion or a link to it if its available somewhere.

2) I think what is lost in some threads is the nuances that are seen (in IS, ASET AND HA viewer) are being overlooked. They can tell us a lot about the stone without having to take a sarin and compare deviations in crown and pavillion angles.

i) ''hotspots'' showing areas of increased fire and scintillation
ii) what I call ''rabbit ears'' on the edge of the stone and their relaitve sizes showing variations in girdle thickness and painting and digging http://journal.pricescope.com/Articles/45/1/Visible-Effects-of-Painting--Digging-on-Superideal-Diamonds.aspx (images taken from here)
iii) different lengths of arrows showing assymetry and tilt from various factors in idealscope images
iv) hearts images (one heart differnt heart size, variation in heart brightness, size of heart cleft, seperation of heart from the arrows) and their implications of proper interpretation of imperfectly formed hearts, clefts , uneven brightness in the two halves of a heart etc. http://journal.pricescope.com/Articles/65/1/Hearts-and-Arrows-Diamonds-and-The-Basics-of-Diamond-Cutting.aspx
v) arrows images (arrow does not meet the girdle, variation in the lengths and thickness of the arrows etc.)

I am sure there are others nuances I may have missed and would welcome mention of these as well.

But there is also a problem if we are too critical and don''t realize how suttle some of these nuances are and how ''near perfect'' numbers or images also correlate to excellent performers in real life observation.
If we add enhanced layers of testing for things that may not even be seen by the average consumer, caution also needs to be taken that these critiques are put into proper context and that near top performing stones aren''t rejected for ''mind clean'' issues.

CCL,

I like that you are trying to consider and read the nuances of various pictures, but what you call ''hotspots'' still needs to be proven to be connected to increased fire and scintillation. From what I understand, it does not really impact scintillation and there might be a secondary or tertiary minimally beneficial effect on observed fire in such an obstruction-area.

Live long,

 

[rak4me]

Some opposing viewpoints on the comparison of a real-image ASET vs. the computer-generated one on the AGS report:

Karl_K wrote: The image on the report is a computer generated face up image from a scan that often has serious problems.
A properly taken real image ASET is much more accurate.

Todd Gray wrote: However the point which I am trying to make in my original post, is that I do not think that consumers should be making a decision to purchase a diamond based on how it looks in the photograph provided of the diamond as seen from a single top down vantage point through an ASET scope - because it is an incomplete analysis of the diamond in comparison to the Light Performance analysis conducted by the AGS Laboratory in their ASET platform which considers the diamond from literally hundreds of vantage points.

So what should the diamond shopper do? Perhaps the best thing is to understand the pros/cons of each image, and evaluate each image on its own merit with that in mind. The AGS scan is more comprehensive, but maybe it''s in that complexity that the serious problems lie? Karl_K, could you explain more about what the serious problems could be? The real-life ASET scope image shows the diamond in its best possible "pose" and has limited information--but hey, if that image looks good, that''s still a big positive, correct?

ChunkyCushionLover wrote: But there is also a problem if we are too critical and don''t realize how suttle some of these nuances are and how "near perfect" numbers or images also correlate to excellent performers in real life observation. If we add enhanced layers of testing for things that may not even be seen by the average consumer, caution also needs to be taken that these critiques are put into proper context and that near top performing stones aren''t rejected for "mind clean" issues.

I think this is an important idea to keep in mind, that there is always a point of diminishing returns after which you can keep spending $$$ but even the best eyes in the business would have to spend a few minutes scrutinizing your rock before they could find a nit to pick. To help everyone out there who posts IS and ASET images and holds their breath for responses from the community, can the experts chime in on how "poor" an IS or ASET would have to be before you can really notice a difference in performance? On a scale from 1-10 (10 being best), and if most images posted here average 7 or 8, at which point does it start to become noticeable? A tough question, but if a few people can take a shot at it and form some manner of consensus, a lot of people would be interested in the answers.

 

[Paul-Antwerp]

Date: 4/22/2010 11:16:01 PM
Author: rak4me

ChunkyCushionLover wrote: But there is also a problem if we are too critical and don''t realize how suttle some of these nuances are and how ''near perfect'' numbers or images also correlate to excellent performers in real life observation. If we add enhanced layers of testing for things that may not even be seen by the average consumer, caution also needs to be taken that these critiques are put into proper context and that near top performing stones aren''t rejected for ''mind clean'' issues.

I think this is an important idea to keep in mind, that there is always a point of diminishing returns after which you can keep spending $$$ but even the best eyes in the business would have to spend a few minutes scrutinizing your rock before they could find a nit to pick. To help everyone out there who posts IS and ASET images and holds their breath for responses from the community, can the experts chime in on how ''poor'' an IS or ASET would have to be before you can really notice a difference in performance? On a scale from 1-10 (10 being best), and if most images posted here average 7 or 8, at which point does it start to become noticeable? A tough question, but if a few people can take a shot at it and form some manner of consensus, a lot of people would be interested in the answers.

The few cases that I know of a consumer actually comparing in-real-life stones of which the IS and ASET looked great, they still experienced a big difference in performance.

As such, this should not be a surprise, because the IS and ASET are rejection-tools of brightness, and give no direct information on fire or scintillation.

Live long,

 

[ChunkyCushionLover]

Date: 4/22/2010 6:43:24 AM
Author: Paul-Antwerp

Date: 4/21/2010 4:51:25 PM
Author: ChunkyCushionLover


Great thread Todd, got me thinking a bit about rounds and interpreting images again.

Couple of points:

1) The methodology used for grading disperion(there is no fire metric) in the AGS/PGS system and its foundations are found in this paper I didn''t purchase the PGS software or its supporting documentation so I don''t have the specific grading information. I would be interested to know specifically a lot of the fine details of the calculation for dispersion from those fire maps. Specifically for all the light performance categories I am interested to know how they weight each of the images. I read some time ago faceup was most heavily weighted then -5 degrees on each side is worth less, -10 on each side even less. I hope someone wouldn''t mind posting some of this for a lot of the catergories of PGS grading like Brightness and Dispersion or a link to it if its available somewhere.

2) I think what is lost in some threads is the nuances that are seen (in IS, ASET AND HA viewer) are being overlooked. They can tell us a lot about the stone without having to take a sarin and compare deviations in crown and pavillion angles.

i) ''hotspots'' showing areas of increased fire and scintillation
ii) what I call ''rabbit ears'' on the edge of the stone and their relaitve sizes showing variations in girdle thickness and painting and digging http://journal.pricescope.com/Articles/45/1/Visible-Effects-of-Painting--Digging-on-Superideal-Diamonds.aspx (images taken from here)
iii) different lengths of arrows showing assymetry and tilt from various factors in idealscope images
iv) hearts images (one heart differnt heart size, variation in heart brightness, size of heart cleft, seperation of heart from the arrows) and their implications of proper interpretation of imperfectly formed hearts, clefts , uneven brightness in the two halves of a heart etc. http://journal.pricescope.com/Articles/65/1/Hearts-and-Arrows-Diamonds-and-The-Basics-of-Diamond-Cutting.aspx
v) arrows images (arrow does not meet the girdle, variation in the lengths and thickness of the arrows etc.)

I am sure there are others nuances I may have missed and would welcome mention of these as well.

But there is also a problem if we are too critical and don''t realize how suttle some of these nuances are and how ''near perfect'' numbers or images also correlate to excellent performers in real life observation.
If we add enhanced layers of testing for things that may not even be seen by the average consumer, caution also needs to be taken that these critiques are put into proper context and that near top performing stones aren''t rejected for ''mind clean'' issues.

CCL,

I like that you are trying to consider and read the nuances of various pictures, but what you call ''hotspots'' still needs to be proven to be connected to increased fire and scintillation. From what I understand, it does not really impact scintillation and there might be a secondary or tertiary minimally beneficial effect on observed fire in such an obstruction-area.

Live long,

Any reference paper you could suggest to support that statement?

 

[ChunkyCushionLover]

Date: 4/19/2010 2:29:37 PM
Author:Todd Gray
This is a rant, I can already feel the flames of Haites licking upon my boot heels, but hopefully it will evolve into a discussion which will provide insight into the inner realm of diamond buying as seen from the perspective of the industry and my friends here on PS who take time out of their daily lives to provide advice to diamond buying consumers who are often looking for a quick fix to their diamond buying dilemma.

Hardly a day passes by where I do not see multiple threads on RT where consumers ask ''is this a good diamond?'' and offer only the information provided on the lab report, here I made this stone up:

Lab: GIA
Measurements: 6.47 - 6.50 x 3.99 mm
Weight: 1.02
Total depth: 61.4%
Table diameter: 55%
Crown angle: 34.5 degrees
Pavilion angle: 40.8 degrees
Girdle: thin to medium, faceted
Culet: none
Polish & Symmetry: Excellent

Everything looks good at first glance, so many people will likely tell the customer ''looks good!''

A few people will advise the customer to ask the seller for pictures of the diamond as seen through a Hearts & Arrows viewer, an Ideal Scope and an ASET... Then when the images are provided, if they look decent (''lots of red in the ASET, looks good!'') then the customer will probably again be told ''looks good'' and sometimes this advice is fine, but other times I have to say as an experienced diamond buyer that I''m looking at part of the image and screaming ''No, No, NO!'' at my monitor, but I''m prohibited from saying anything because I''m a vendor and quite often the name of the other vendor has been mentioned in the thread, or the identity of the vendor could easily be identified by simply running a search for the diamond within the PS search engine (don''t bother with my example, once again, I made the stone up).

I''m going to be so bold as to take the probable unpopular position that the ASET not be used to ''evaluate'' diamonds which have not been graded by the AGS Laboratory on the Platinum grading platform, and the reason I''m going to do so is because when the AGS uses the ASET to evaluate a diamond for brightness, they do NOT do so from the single static view that is commonly relied upon here on PS to determine whether a diamond ''looks good'' or not - when the AGSL uses the ASET to evaluate diamonds, they do so using ray tracing which considers the diamond as seen from hundreds of different perspectives and the Light Performance grade is conclusive of the results of all of the data - not the single static view, which happens to show the diamond from the best possible vantage point! The ASET evaluation is distinctly different than that provided by an Ideal Scope or Hearts & Arrows viewer which are designed to view the diamond from a single static vantage point.

~~~~~~~~~~~~
Proportions: even my own preferred range of 59 - 61.8%; 53 - 58%; 34.3 - 34.8; 40.6 - 40.9; etc. etc. is ONLY the beginning... So much more is waiting for you down the rabbit hole.
~~~~~~~~~~~~

Many people who are new to PS might not be aware that the measurements for Crown & Pavilion angle as stated on the lab reports reflect the average of eight measurements taken per section... For this reason, it is important to advise consumers to obtain the individual measurements which the average is based upon and preferably a diagram from the Sarin | OGI | Helium machine used to measure the diamond to study ''the flow'' of the facets to determine where the High / Low measurements occur / transition and to what degree the cutter adjusted the facets as the diamond was cut... In other words, when you look at the kite shaped Bezel facets on the top of the stone, say the average of 34.5 degrees is based on a spread of 34.2 - 34.8 degrees, most people would agree that this is a pretty minimal spread and without seeing ''the flow'' of the facets, they might tell you that the diamond is ''tight'' and you might purchase the diamond. But if you also looked at the facet-by-facet diagram for the diamond, it might tell a different story... Let''s say that you''re looking at the diagram of the Crown as if it were the face of a clock (from left to right) and the measurements start with 34.2 | 34.3 | 34.4 | 34.5 | 34.6 | 34.7 | 34.8 | 34.3

What additional insight would this provide? Well besides the fact that the diagram looks pretty cool (and the 3D Sarin file looks even cooler than that!) it would tell you that the table of the cutting wheel was tilted slightly, Doh! AND it would tell you that the cutter had to make an adjustment to even things out on the last Bezel facet! And if you looked at the same diagram structure for the facets which make up the Pavilion angle and determined that it was also cut at a tilt and the cutter had to make additional adjustments, you might realize that a particular ''ideal cut'' diamond is not as ''ideal'' as you might want it to be... Hmmm, I wonder what the stone would look like if the crown and the pavilion sections were tilted in opposite directions? What? You say that it could never happen? Well, you do realize that the majority of diamonds are cut ''piece-mail'' with different cutters cutting different sections of the diamonds as dictated by their station, thus each cutter sets their own wheel and makes adjustments to the stone to complete his or her section based upon what ''precision'' or ''problem'' they are handed by the cutter who cut the section which preceded them... So yea, it can happen.

And then there are the diamonds that have the ''right'' average measurements, such as 34.5 crown angle offset by a pavilion angle of 40.8 degrees, but the crown angle has a spread from 33.5 to 35.5 degrees and the pavilion angle has a spread of 39.8 - 41.8 degrees and the crown facets read like this: 33.5 | 35.5 | 33.5 | 35.5 | 33.5 | 35.5 | 33.5 | 35.5 and I''m telling you, I''ve seen it! In fact, I rejected 40 of 40 ''ideal cut'' diamonds like this from one particular cutter a few years ago right before the AGS Laboratory changed the way they determine whether a diamond is ''ideal cut'' or not - and it was this type of cutting that caused the AGS Laboratory to change how they graded diamond cut quality - don''t take my word for it, call the lab!

So P-L-E-A-S-E look past the average numbers on the lab reports and look past the basic data provided for the high and low measurements and look at the actual structure of the diamond! That''s what experienced diamond buyers do... This is the type of information that is probably only important to the 5-6% of consumers who find themselves on PS, but it drives me nuts that I keep seeing people rubber stamp diamond quality based on such limited information.

~~~~~~~~~~~~
Inclusions:
~~~~~~~~~~~~

Even if the diamond has been carefully evaluated by the seller, as I and many other professionals here on PS do with every diamond that we sell, I firmly believe that it is the best interest of the customer to have the diamond evaluated by an independent appraiser of their choosing, because as sellers we represent ourselves and the interests of the companies which we represent and the independent appraisers represent the client and the interests of the client.

Todd,

I''ve seen in another forum a regular poster from stating that a crown or pavillion deviation (max - min) over 0.5 degrees is considered too much for them. How accurate do you think making an interpretation based on these numbers which are available on abbreviated facetware reports is? A facetware report from sarin or helium will not tell you the "flow" or individual mesurements and even vendors who provide these abbreviated reports are few and far between.

How does an experienced buyer get the individual angles, there is only one website to my knowledge that provides complete enough helium reports for rounds and that is GOG. When you say experienced buyer I have no idea are you talking about tradesmembers? Do cutters provide you with full sarin reports before you call in the stones?

Please tell me what you see in images with examples of IS or ASET of near HA stones when there is significant deviation in "flow" of the pavillion mains or crown angles. I know you could tell this from a heats image or arrows image, but what about from IS? As we often do not get to look at ha images on near HA stones.

 

[Karl_K]

Date: 4/22/2010 11:16:01 PM
Author: rak4me
Some opposing viewpoints on the comparison of a real-image ASET vs. the computer-generated one on the AGS report:



Karl_K wrote: The image on the report is a computer generated face up image from a scan that often has serious problems.

A properly taken real image ASET is much more accurate.



Todd Gray wrote: However the point which I am trying to make in my original post, is that I do not think that consumers should be making a decision to purchase a diamond based on how it looks in the photograph provided of the diamond as seen from a single top down vantage point through an ASET scope - because it is an incomplete analysis of the diamond in comparison to the Light Performance analysis conducted by the AGS Laboratory in their ASET platform which considers the diamond from literally hundreds of vantage points.



So what should the diamond shopper do? Perhaps the best thing is to understand the pros/cons of each image, and evaluate each image on its own merit with that in mind. The AGS scan is more comprehensive, but maybe it's in that complexity that the serious problems lie? Karl_K, could you explain more about what the serious problems could be? The real-life ASET scope image shows the diamond in its best possible 'pose' and has limited information--but hey, if that image looks good, that's still a big positive, correct?

The biggest problem with scan based images is garbage in garbage out.
Even for rounds if you go through the reports and compare them to real aset images you will find errors in the report images at times.
Most of the time it isn't that bad for rounds but for fancies it is a much bigger issue.
Then there are some issues with ASET itself.
What should a consumer do? get multiple data points and deal with a vendor who is picky and knowledgeable about what they sell and get some help on PS to evaluate the information provided if they don't want to learn it themselves.

 

[ChunkyCushionLover]

Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?
This is a "Near HA" round.

 

[Serg]

Date: 4/23/2010 3:05:17 PM
Author: ChunkyCushionLover
Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?

This is a ''Near HA'' round.

CCL,

nobody could give transparent correlation neither between level of asymmetry ASET/IS images and diamond performance nor between deviation in scann report and diamond performance . I do not know any scientific research in such field. ( I am not speaking about interconnection between optical asymmetry and Leakage . I am speaking about connection between asymmetry and performance. These are two quite different issues ( even if most "PS consumers and prosumers" do not see difference between these two issues)

of course asymmetry changes performance , but in same time asymmetry could decrease and increase different parts of Diamond Performance ( for example reduce Fire and increase Scintillation )

 

[WinkHPD]

Date: 4/23/2010 3:05:17 PM
Author: ChunkyCushionLover

Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?
This is a ''Near HA'' round.

You may not see any deviation from the ideal in the sarin. Ideal has nothing to do with H&A and everything to do with optical symmetry. The two are NOT related or co dependant in any way. It is entirely possible to have ideal cut diamonds without H&A and also to have H&A with diamonds well outside the ideal range.

As for what is causing the broken arrows, I will leave that for someone like Paul to answer.

Wink

 

[WinkHPD]

See what happens when you answer the phone when posting, someone else comes along and says it.

Wink

 

[ChunkyCushionLover]

Date: 4/23/2010 3:19:04 PM
Author: Serg

Date: 4/23/2010 3:05:17 PM
Author: ChunkyCushionLover

Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?

This is a ''Near HA'' round.

CCL,

nobody could give transparent correlation neither between level of asymmetry ASET/IS images and diamond performance nor between deviation in scann report and diamond performance . I do not know any scientific research in such field. ( I am not speaking about interconnection between optical asymmetry and Leakage . I am speaking about connection between asymmetry and performance. These are two quite different issues ( even if most ''PS consumers and prosumers'' do not see difference between these two issues)

of course asymmetry changes performance , but in same time asymmetry could decrease and increase different parts of Diamond Performance ( for example reduce Fire and increase Scintillation )

Serg,

Respectfully please don''t sidetrack the question with a debate about how or if ASET/IS correlates to diamond performance or anything other than brightness.
My question is how optical symmetry or lack thereof as seen in ASET/IS correlates to facet assymetry and if it can be used as a predictor for localized physical facet deviation.

For example, painting and digging can be observed in ASET and IS and Peter Yantzer did make correlations. http://journal.pricescope.com/Articles/15/8/The-Effects-of-Indexed-Upper-Half-Facets.aspx.

 

[ChunkyCushionLover]

Date: 4/23/2010 3:27:04 PM
Author: Wink

Date: 4/23/2010 3:05:17 PM
Author: ChunkyCushionLover


Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?
This is a ''Near HA'' round.

You may not see any deviation from the ideal in the sarin. Ideal has nothing to do with H&A and everything to do with optical symmetry. The two are NOT related or co dependant in any way. It is entirely possible to have ideal cut diamonds without H&A and also to have H&A with diamonds well outside the ideal range.

As for what is causing the broken arrows, I will leave that for someone like Paul to answer.

Wink

I am using ideal to mean no deviation in angle not "ideal" light performance.

Yes they are co-dependant, would be a fluke to get perfect optical symmetry without physical facet symmetry.

 

[WinkHPD]

Date: 4/23/2010 6:25:47 PM
Author: ChunkyCushionLover

Date: 4/23/2010 3:27:04 PM
Author: Wink

Date: 4/23/2010 3:05:17 PM
Author: ChunkyCushionLover



Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?
This is a ''Near HA'' round.

You may not see any deviation from the ideal in the sarin. Ideal has nothing to do with H&A and everything to do with optical symmetry. The two are NOT related or co dependant in any way. It is entirely possible to have ideal cut diamonds without H&A and also to have H&A with diamonds well outside the ideal range.

As for what is causing the broken arrows, I will leave that for someone like Paul to answer.

Wink

I am using ideal to mean no deviation in angle not ''ideal'' light performance.

Yes they are co-dependant, would be a fluke to get perfect optical symmetry without physical facet symmetry.

Actually not. EightStar often got less than Excellent Symmetry from GIA as they cut their diamonds for optical symmetry and did not care if some of the facet junctions did not perfectly line up. While I will agree that you have to have a plan to get it other than accidentally, you can have fair to good physical symmetry while having a perfect H&A pattern.

I was however talking about ideal light performance and H&A, as many Ideal cut diamonds do not display H&A.

Wink

 

[Dancing Fire]

Date: 4/21/2010 12:19:31 PM
Author: Todd Gray

Dancing Fire, oh I do like the minimal range of variance that you''ve specified
The lower the amount of deviation (the official gemological term) between the high and low measurements, the better the potential for light return... In the real world, a deviation of 0.0 - 0.5 is probably realistic and as I recall, I''ve only seen 0.0 - 0.1 a few times and I think I hesitated to sell the stone.

why Todd?

too perfect?

 

[Garry H (Cut Nut)]

Date: 4/23/2010 7:03:23 PM
Author: Wink

Actually not. EightStar often got less than Excellent Symmetry from GIA as they cut their diamonds for optical symmetry and did not care if some of the facet junctions did not perfectly line up. While I will agree that you have to have a plan to get it other than accidentally, you can have fair to good physical symmetry while having a perfect H&A pattern.

I was however talking about ideal light performance and H&A, as many Ideal cut diamonds do not display H&A.

Wink

Hi Wink, I thought GIA symmetry downgrades for 8* were often from girdle variations because of the painting?
(no need to answer though - as it takes this thread off topic)

 

[WinkHPD]

Date: 4/23/2010 7:45:50 PM
Author: Garry H (Cut Nut)

Date: 4/23/2010 7:03:23 PM
Author: Wink

Actually not. EightStar often got less than Excellent Symmetry from GIA as they cut their diamonds for optical symmetry and did not care if some of the facet junctions did not perfectly line up. While I will agree that you have to have a plan to get it other than accidentally, you can have fair to good physical symmetry while having a perfect H&A pattern.

I was however talking about ideal light performance and H&A, as many Ideal cut diamonds do not display H&A.

Wink

Hi Wink, I thought GIA symmetry downgrades for 8* were often from girdle variations because of the painting?
(no need to answer though - as it takes this thread off topic)

Also for facet junctions not meeting perfectly. They cut for the pattern, nothing else mattered. I could be wrong, it has been several years since I was an EightStar dealer, but that is my memory of what we were told at the time.

Wink

P.S. I believe Todd is correct. The numbers and viewers are great rejection tools, but the final selection tool has to be the eye, and the taste, of the buyer.

 

[Garry H (Cut Nut)]

Date: 4/21/2010 4:52:41 PM
Author: DiaGem

Date: 4/21/2010 3:13:21 PM
Author: Karl_K

Date: 4/21/2010 1:36:32 PM
Author: oldminer
Thanks for the advisory. Seems interesting, at least to me, that the symmetry we can measure objectively may have a noticeable range before the symmetry grade is lowered to the Very Good step. As a follow-up,. Are there a range of crown angles from high to low which would lower always the Symmetry grade from Ex to VG? Such grade setting points always are of interest although not the way anyone would suggest to select a diamond.

At some point it becomes physically impossible to line them up at the ex level that varies by facet, is there a downgrade before that point?

From my rather short experience in this cutting arena I dont think there is a clear border that differentiate between X & VG.

its a combination of numerous factors...

For example, take Todd Gray''s comment above

''what if the flow of the facets went something like 34.5 | 34.9 | 34.8 | 34.7 | 34.9 | 34.8 | 34.7 | 34.9 | it might be something you would want to take into consideration?''

And then combining the following Pav angles in correlation: ''40.4 | 40.7 | 40.8 | 40.9 | 40.8 | 40.7 | 40.9 | 41.0 |''


I didnt test it..., but in such case (I believe) due to the nature of the overall precision cut other parameters would move out of sync of the overall excellent symmetry level required, like culet/table (tilt) off-center or a wide range of girdle thickness that would automatically display the ''above mentioned ''border''.

Many more examples are available depending on facet designs.

On a side note to all involved in this discusion..., please take into consideration that scan error stands at 3-4 tenths of a degree (AND NOT ALWAYS AT THE SAME POSITION

).

Deare Todd, Dave and Ira,
I again link you to this article which shows a coommon issue
http://www.gemology.ru/cut/english/symmetry/6.htm

The cause of such variations can be as simple as a little bit of grit under the table when the stope is plaed in the dop. The stone in this example had GIA Good symmetry, yet it was a fine looking stone that one of my clients is happily wearing.

 

[emeraldlover1]

Date: 4/20/2010 1:32:47 PM
Author: yssie
It''s the new members looking for the yea/nay on one diamond or another who don''t know this, and they''re the ones who are going to take those ''guides'' as gospel. The consumers who know better - well, know better.



Maybe a new policy - just don''t say a word until they''ve read the tutorial, every page of it! So everyone fully understands why Garry''s cut advisor, Lorelei''s cheat sheet, an IS image.. are very helpful tools that should be used judiciously, allowing for manoeuvring. Knowing the limitations of the tools you''re using is always good practice.

I think that is just a little unrealistic. Not everyone has the time so they come here hoping that maybe some pro consumers and industry folks can help out. Asking them to do extensive research on this forum before they ask a question isn''t very supportive. Even if they did do all of those things it may take longer to grasp the concepts and make sense of all the information. Some people just don''t care to over analyze or deeply analyze something. I think the beauty of this site is that there are members that are willing to help new people do that.

I would also hope that most people are intellegent enough to not take everything on one particular site as gospel. I would hope that we could give new or prospective participants of this forum a little credit.

 

[yssie]

Date: 4/23/2010 8:04:42 PM
Author: emeraldlover1

Date: 4/20/2010 1:32:47 PM
Author: yssie
It's the new members looking for the yea/nay on one diamond or another who don't know this, and they're the ones who are going to take those 'guides' as gospel. The consumers who know better - well, know better.



Maybe a new policy - just don't say a word until they've read the tutorial, every page of it! So everyone fully understands why Garry's cut advisor, Lorelei's cheat sheet, an IS image.. are very helpful tools that should be used judiciously, allowing for manoeuvring. Knowing the limitations of the tools you're using is always good practice.

I think that is just a little unrealistic. Not everyone has the time so they come here hoping that maybe some pro consumers and industry folks can help out. Asking them to do extensive research on this forum before they ask a question isn't very supportive. Even if they did do all of those things it may take longer to grasp the concepts and make sense of all the information. Some people just don't care to over analyze or deeply analyze something. I think the beauty of this site is that there are members that are willing to help new people do that.

I would also hope that most people are intellegent enough to not take everything on one particular site as gospel. I would hope that we could give new or prospective participants of this forum a little credit.

I know that when I first found PS a couple of years ago I certainly would have taken anything like a "cheat sheet" as gospel. If it was 34.0, great. 33.9 - nope! I'm neither unintelligent nor lazy, I simply would have assumed (correctly) that the poeple writing the cheat sheet knew far more than I did and (incorrectly) that it's better to be safe and adhere to their exact words than to take a risk and wind up with something dreadful. And so I would have missed out on a whole type of performance that I absolutely adore.


I do find it amusing when someone comes into RT and asks a question that's answered word for word in the first page or two of the tutorial...

 

[emeraldlover1]

yssie...I totally understand what you are saying and I did not intend to imply that you aren''t intellegent by taking someone elses opinion as fact. I simply posted to offer a different prespective. People have different wants and needs. The reason these posts come up all the time is because there isn''t an exact way to determine how to pick a diamond based on numbers and not every consumer wants to spend the time to figure out why. We can only be there to offer support and suggestions.

Additionally, it takes a few days or longer to get adjusted to where information is in any forum. People are always going to ask questions that have been answered before as well as not be able to find the "cheat sheets". You can always point them in that direction and hope that they try and understand the information or you can copy and paste the suggestions like CCL often does.

My inital post was sparked in response to it being unrealistic to make a policy that demands members of the site read and understand consumer suggestions prior to posting.

 

[yssie]

I didn't find your post insulting or offensive at all

I'm a researcher, I research $100 purchases - so the idea of not wanting to know everything about something I'm spending thousands of dollars on is so completely foreign to me, I don't pretend to understand it. It also means that when I use a microscope, I know what 100x magnification means - and what it doesn't mean.


I don't like the cheat sheet or the HCA. I think they are fantastic tools, but I think the people who are going to use them are the same people who are going to misuse (ie. overuse) them regardless of the big fat DISCLAIMER at the top. And I think that's a real pity, but I don't see any way to prevent it.

 

[emeraldlover1]

Date: 4/23/2010 9:10:42 PM
Author: yssie
I didn''t find your post insulting or offensive at all

I''m a researcher, I research $100 purchases - so the idea of not wanting to know everything about something I''m spending thousands of dollars on is so completely foreign to me, I don''t pretend to understand it. It also means that when I use a microscope, I know what 100x magnification means - and what it doesn''t mean.


I don''t like the cheat sheet or the HCA. I think they are fantastic tools, but I think the people who are going to use them are the same people who are going to misuse (ie. overuse) them regardless of the big fat DISCLAIMER at the top. And I think that''s a real pity, but I don''t see any way to prevent it.

Yeah, sadly I know exactly what you mean. I also think some people don''t know how to use them even after trying to understand them. Who reads disclaimers anyway? LOL, I''m kidding.

 

[Karl_K]

Date: 4/23/2010 3:05:17 PM
Author: ChunkyCushionLover
Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?

This is a 'Near HA' round.

Cant comment on the diamond itself.
In general:

This type of variation if it shows up at all on a sarin scan will only show up on the 3d scan/viewer.
A full helium report would also give a clue.
The standard sarin report will not show it.
9 times out of 10 variation in the arrows is really variation in the lower girdles affecting the mains.
The other time it is a wide variation in angle and or placement of the mains.
This also explains why you could have .1 variation in the mains angle with broken arrows and wacky hearts.
Look at a wire diagram of a diamond and you will see why that makes sense.

Also read and understand this article:
http://journal.pricescope.com/Articles/68/1/Do-the-pavilion-mains-drive-light-return-in-the-modern-round-brilliant.aspx

 

[Serg]

Date: 4/23/2010 6:19:02 PM
Author: ChunkyCushionLover

Date: 4/23/2010 3:19:04 PM

Author: Serg

Date: 4/23/2010 3:05:17 PM

Author: ChunkyCushionLover


Anyone care to comment on the appearance of these two images and what deviation from ideal you would see in a sarin that causes the broken offset arrows and the areas showing green in the ASET?


This is a 'Near HA' round.

CCL,


nobody could give transparent correlation neither between level of asymmetry ASET/IS images and diamond performance nor between deviation in scann report and diamond performance . I do not know any scientific research in such field. ( I am not speaking about interconnection between optical asymmetry and Leakage . I am speaking about connection between asymmetry and performance. These are two quite different issues ( even if most 'PS consumers and prosumers' do not see difference between these two issues)


of course asymmetry changes performance , but in same time asymmetry could decrease and increase different parts of Diamond Performance ( for example reduce Fire and increase Scintillation )

Serg,


Respectfully please don't sidetrack the question with a debate about how or if ASET/IS correlates to diamond performance or anything other than brightness.

My question is how optical symmetry or lack thereof as seen in ASET/IS correlates to facet assymetry and if it can be used as a predictor for localized physical facet deviation.


For example, painting and digging can be observed in ASET and IS and Peter Yantzer did make correlations. http://journal.pricescope.com/Articles/15/8/The-Effects-of-Indexed-Upper-Half-Facets.aspx.

CCL,

re:My question is how optical symmetry or lack thereof as seen in ASET/IS correlates to facet assymetry and if it can be used as a predictor for localized physical facet deviation.

What is practical sense in your this question for consumer?

Neither ASET asymmetry nor deviation in scan report have good correlation with LAB grading reports.
All of them have bad correlation with performance . If consumer are interesting to buy Round craftsmanship diamond he needs study H&A images.
what is reason in such case to discuss correlation between ASET and scan report deviations ?
Much more useful to discuss about correlation between H&A and scan report deviations.
ASET/IS have different propose and they are not so sensitive for cut asymmetry.

Industry needs a lot of important research. But we waste a lot time for empty discussions on PS. Could we use our time on PS more useful for industry?

 

[Lorelei]

Date: 4/23/2010 9:10:42 PM
Author: yssie
I didn''t find your post insulting or offensive at all

I''m a researcher, I research $100 purchases - so the idea of not wanting to know everything about something I''m spending thousands of dollars on is so completely foreign to me, I don''t pretend to understand it. It also means that when I use a microscope, I know what 100x magnification means - and what it doesn''t mean.


I don''t like the cheat sheet or the HCA. I think they are fantastic tools, but I think the people who are going to use them are the same people who are going to misuse (ie. overuse) them regardless of the big fat DISCLAIMER at the top. And I think that''s a real pity, but I don''t see any way to prevent it.

There really isn''t any way to prevent it, all we can do is our best to help each individual according to their needs and circumstances. We can''t make a perfect buying experience for every poster and give them all the tools to make that happen, we can try and continue to try but in the end dealing with such a diverse group of buyers with incredibly varied needs we can only offer the best help we can to empower the consumer towards the best choice for them according to THEIR requirements.

 

[Garry H (Cut Nut)]

Date: 4/24/2010 5:34:56 AM
Author: Lorelei

Date: 4/23/2010 9:10:42 PM
Author: yssie
I didn''t find your post insulting or offensive at all

I''m a researcher, I research $100 purchases - so the idea of not wanting to know everything about something I''m spending thousands of dollars on is so completely foreign to me, I don''t pretend to understand it. It also means that when I use a microscope, I know what 100x magnification means - and what it doesn''t mean.


I don''t like the cheat sheet or the HCA. I think they are fantastic tools, but I think the people who are going to use them are the same people who are going to misuse (ie. overuse) them regardless of the big fat DISCLAIMER at the top. And I think that''s a real pity, but I don''t see any way to prevent it.

There really isn''t any way to prevent it, all we can do is our best to help each individual according to their needs and circumstances. We can''t make a perfect buying experience for every poster and give them all the tools to make that happen, we can try and continue to try but in the end dealing with such a diverse group of buyers with incredibly varied needs we can only offer the best help we can to empower the consumer towards the best choice for them according to THEIR requirements.

Lorelei in the post above Sergey is asking a question like:- "how can we make it easy?"

This is not as good as it gets.
The industry has inflicted its features and jargon based grading system on consumers and calls it "consumer protection".
It ain''t that at all Baby!

 

[Lorelei]

Date: 4/24/2010 6:46:21 AM
Author: Garry H (Cut Nut)

Date: 4/24/2010 5:34:56 AM
Author: Lorelei

Date: 4/23/2010 9:10:42 PM
Author: yssie
I didn't find your post insulting or offensive at all

I'm a researcher, I research $100 purchases - so the idea of not wanting to know everything about something I'm spending thousands of dollars on is so completely foreign to me, I don't pretend to understand it. It also means that when I use a microscope, I know what 100x magnification means - and what it doesn't mean.


I don't like the cheat sheet or the HCA. I think they are fantastic tools, but I think the people who are going to use them are the same people who are going to misuse (ie. overuse) them regardless of the big fat DISCLAIMER at the top. And I think that's a real pity, but I don't see any way to prevent it.

There really isn't any way to prevent it, all we can do is our best to help each individual according to their needs and circumstances. We can't make a perfect buying experience for every poster and give them all the tools to make that happen, we can try and continue to try but in the end dealing with such a diverse group of buyers with incredibly varied needs we can only offer the best help we can to empower the consumer towards the best choice for them according to THEIR requirements.

Lorelei in the post above Sergey is asking a question like:- 'how can we make it easy?'

This is not as good as it gets.
The industry has inflicted its features and jargon based grading system on consumers and calls it 'consumer protection'.
It ain't that at all Baby!

And that my dear Watson is the crux of the matter and what we are all working towards! For my post above, I was speaking of overuse and reliance on various cheat sheets and the HCA, as an example time and time again I have to remind and explain to consumers that the HCA isn't a selection tool but is used for rejection, maybe a rewrite of the usage stressing that might be an idea if you have time Garry?

We are a long way from things being as good as they can get, we have come a long way certainly but there is still much to be done. That includes not taking the industry grading systems and various jargons not face value ( I quite agree) and also keeping advice given here relevant and consumer friendly. There is a lot of work in front of us and "how can we make it easy?" is a great goal to keep in mind for the benefit of consumers.