What is the difference between Cut Grading and Cut Rejection

[Rockdiamond]

Re: What is the difference between Cut Grading and Cut Rejec

The term "performance" is not applicable in this sense, in my opinion.
We can test two pieces of cloth for performance.
Light passing through a diamond, and the interpretation of it should not be put into the same category as something which has textile properties- and can truly be shown to "perform" better.

In this sense- in answer to Garry's original question, if we introduce "performance" there is no difference between cut grading and cut rejection without the proper context.

 

[senorpacifico]

Re: What is the difference between Cut Grading and Cut Rejec

Love this post. An excellent topic and excellent opinions and analysis of different sides of the "spectrum ". Thank you all.

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

The term "performance" is not applicable in this sense, in my opinion.
We can test two pieces of cloth for performance.
Light passing through a diamond, and the interpretation of it should not be put into the same category as something which has textile properties- and can truly be shown to "perform" better.

In this sense- in answer to Garry's original question, if we introduce "performance" there is no difference between cut grading and cut rejection without the proper context.

re:In this sense- in answer to Garry's original question, if we introduce "performance" there is no difference between cut grading and cut rejection without the proper context.

There is Huge difference between Cut grading and Cut rejection systems if we speak about grading Light performance.

Cut rejection system blocks any deviation from preselected reference cut, diamond. ( just remind you history about painting in round diamonds).
Cut rejection system blocks improving cut to receive better Performance.
Cut rejections system does not demand neither understanding of Beauty nor language for communication between retail and consumer.
Cut rejection systems say nothing about difference between 2 diamonds with same rank .

it is not full list about difference between Rejection and Score systems if we speak about Light performance

I do not know any rejections system to grade clothing Performance, wine performance, glasses performance, car performance,..etc But I see only rejection systems to grade Diamond Light performance.
Diamond industry is unique .

 

[denverappraiser]

Re: What is the difference between Cut Grading and Cut Rejec

I do not know any rejections system to grade clothing Performance, wine performance, glasses performance, car performance,..etc But I see only rejection systems to grade Diamond Light performance.
Diamond industry is unique .

A few decades ago, administrators at schools would carry rulers with them to measure the hemlines of girls’ skirts. If they were too short, the girl was sent home to change. I don’t know how they enforce the rules these days or even what the rules are but I’m confident that the system of dress codes is basically intact even if the grading standards have changed. That is to say, graders (teachers) have a rejection system for evaluating clothing.

 

[Garry H (Cut Nut)]

Re: What is the difference between Cut Grading and Cut Rejec

Thank you everyone for a really great discussion.

Paul I agree that fire and scintillation are important missing links.
I have been redoing the HCA data base in preparation for an HCA app, and even with the tools in DiamCalc Pro its very difficult - and i am only doing this for one cut - within a narrow range of proportions.

This raises the issue that to me is one of the biggest - how on earth can we ever design new diamond cuts without adequate grading tools.
For example if you use AGSL 3D tools there is a limit placed arbitrarily at AGS 0 for light return, and for fire, and contrast etc. But what if you could design a diamond with 10% more fire and 5% less light return? You could not discover the proportion range using AGSL criteria because they cap their ration at AGS 0 for each data set. (It could be that they could release a developers / designers version that gave raw data?)
Currently AGS could ding such a firey diamond because perhaps its brilliancy failed to get AGS 0.

Neil you made many good points, great points which i hope we can discuss over a Belgian beer in Vegas!
You mentioned how lab grades are used as rejection tools to narrow down the a few or THE ONE. RockDiamond you raised something similar. But Sergey is pointing out that because the system is a rejection system - if you have 2 or 3 diamonds in your final list - you may never choose the right one based on the current 'data'.

And BTW I do apologise if it seems I am picking on AGSL and GIA - but since they occupy or own commercial niches, we can not have this discussion with out mentioning their systems.

For example Draco in his first post mentioned that GIA actually do human observation testing as well as scan data grading. This may be so, but I have not ever seen any rules on the process? And if there are such rules - can the be promoted and used for testing new cut design and applied to other shapes than just the RBC?

And for AGS PGS ssystem - please look at the number of diamonds in our Master Diamond Set http://www.octonus.com/oct/mss/ that recieve 0.0 for the four digital grades - surely there is an opportunity to open the system? But then that would really drive the anal PS shoppers nuts trying to find the AGS -1.5's.

 

[Karl_K]

Re: What is the difference between Cut Grading and Cut Rejec

All of the grading/rejection systems to various degrees give a measurement of potential.
Does the diamond have the potential to perform well under various lighting conditions?
The final test and only test that really matters is the person wearing the ring over a period of time in their environment is happy with it.

Let me share a true story with you.
A local friend of mine was looking for a diamond.
I helped him find a super-ideal diamond, one I would have been proud to put on my Wife's finger.
It flat out rocked :}
I helped him get a price that was just a couple percent over internet pricing.
She absolutely hated it, she wanted a princess cut.
She still to this day, years later teases him about it.

 

[Karl_K]

Re: What is the difference between Cut Grading and Cut Rejec

Rejection to me is pass/fail anything but a yes/no makes it a grading system.
However you can use a grading system as a rejection system.
Not AGS0 - reject
Not GIA EX - reject
So on and so forth.

There is no one tool or test that tells you everything about a diamond, a combination of tools is a good idea.
Even when viewing it in person, how a diamond looks in the store is not a very good indication of how it will look in your living room.

 

[Garry H (Cut Nut)]

Re: What is the difference between Cut Grading and Cut Rejec

Rejection to me is pass/fail anything but a yes/no makes it a grading system.
However you can use a grading system as a rejection system.
Not AGS0 - reject
Not GIA EX - reject
So on and so forth.

There is no one tool or test that tells you everything about a diamond, a combination of tools is a good idea.
Even when viewing it in person, how a diamond looks in the store is not a very good indication of how it will look in your living room.

When I have been in places like Geneva and gone secret shopping with Drena in big name stores with BIG diamonds I made sure Drena's diamonds were clean and then I could compare hers with those in stores. She wore a graduated 5 stone ring and the center heirloom stone is not great, 1ct each shallow cut earrings and a 3ct nice eRing.

Using these as comparison stones it was comparatively easy to asses the performance of diamonds in different lighting in different stores.
This is also not a metric based grading system - "this stone is better than that one and worse than this one". This stone has more fire than that one. This stone is not as bright as that one.
Of course this is how we grade diamond color, but frankly I do not think our color grading system is right (face up color varies from cut type and cut quality when graded as we do upside down).
But since I am doing this beauty or sparkle grading in different environments I am limited to comparisons in unknown lighting which e.g. may not be optimal for separating best fire or best brightness etc just as trying to color grade with too little or the wrong type of light can give poor results.

 

[denverappraiser]

Re: What is the difference between Cut Grading and Cut Rejec

The GIA color grading system is a weird anomoly, but it's the way we do it and it's likely to continue to be the way we do it for the foreseeable future. There are plenty of people out there in industries ranging from printing to optics to paints who REALLY understand color, who have a well thought out language for describing it, and who consider our approach to be laughably primitive. This is nothing new but it's the way diamond people do it and it's almost quaint. It's the reason that the folks at NIST (the people who define to excruciating detail things like a second, a meter or a watt) want nothing to do with our grading systems.

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

The GIA color grading system is a weird anomoly, but it's the way we do it and it's likely to continue to be the way we do it for the foreseeable future. There are plenty of people out there in industries ranging from printing to optics to paints who REALLY understand color, who have a well thought out language for describing it, and who consider our approach to be laughably primitive. This is nothing new but it's the way diamond people do it and it's almost quaint. It's the reason that the folks at NIST (the people who define to excruciating detail things like a second, a meter or a watt) want nothing to do with our grading systems.

Neil,

Developing Color grading system from pavilion side is much more simple task then developing Color grading system from crown.
Developing Rejection cut grading system is much more simple task then developing Score Light Performance system.

Simple rank systems was necessary step to start Big world wide diamond business( to create diamond industry which we use now) .
but now this simplifications block developing diamond business and reduce competitiveness diamond industry against other industries.

 

[Garry H (Cut Nut)]

Re: What is the difference between Cut Grading and Cut Rejec

The GIA color grading system is a weird anomoly, but it's the way we do it and it's likely to continue to be the way we do it for the foreseeable future. There are plenty of people out there in industries ranging from printing to optics to paints who REALLY understand color, who have a well thought out language for describing it, and who consider our approach to be laughably primitive. This is nothing new but it's the way diamond people do it and it's almost quaint. It's the reason that the folks at NIST (the people who define to excruciating detail things like a second, a meter or a watt) want nothing to do with our grading systems.

Neil,

Developing Color grading system from pavilion side is much more simple task then developing Color grading system from crown.
Developing Rejection cut grading system is much more simple task then developing Score Light Performance system.

Simple rank systems was necessary step to start Big world wide diamond business( to create diamond industry which we use now) .
but now this simplifications block developing diamond business and reduce competitiveness diamond industry against other industries.

Since there is no effective beauty performance grading system for all cuts and shapes of diamonds, it's easier to start with a relatively clean slate - whereas the existing color grading system is very hard to change.

 

[diagem]

Re: What is the difference between Cut Grading and Cut Rejec

Since there is no effective beauty performance grading system for all cuts and shapes of diamonds, it's easier to start with a relatively clean slate - whereas the existing color grading system is very hard to change.

Garry, how in the world can you grade beauty?? (LP) Performance perhaps yes but beauty?
Unless you would try to force some kind of norm? And even then you would need participation...

Dont understand the direction you are leading this conversation...

 

[Paul-Antwerp]

Re: What is the difference between Cut Grading and Cut Rejec

Thank you everyone for a really great discussion.

Paul I agree that fire and scintillation are important missing links.
I have been redoing the HCA data base in preparation for an HCA app, and even with the tools in DiamCalc Pro its very difficult - and i am only doing this for one cut - within a narrow range of proportions.

This raises the issue that to me is one of the biggest - how on earth can we ever design new diamond cuts without adequate grading tools.

Seriously, how do you go from the Parker-wine-system or hotel-grading to designing both wine or hotels?

Another question: since all systems are brightness-related only, and since we agree them to be rejection-systems only, what does that in all honesty make of the well-meant advice here on PS? I yesterday received a one-page-comment of a consumer on a stone that he had ordered online, but not had in his hands yet. He described the performance of the stone in such detail, something that I find difficult to do even with the stone in hand. Are we on PS possibly guilty (too) of installing a consumer-cut-grade, based on brightness only, giving the impression that it encompasses all aspects of a diamond's cut?

Live long,

 

[sha4000]

Re: What is the difference between Cut Grading and Cut Rejec

Thank you everyone for a really great discussion.

Paul I agree that fire and scintillation are important missing links.
I have been redoing the HCA data base in preparation for an HCA app, and even with the tools in DiamCalc Pro its very difficult - and i am only doing this for one cut - within a narrow range of proportions.

This raises the issue that to me is one of the biggest - how on earth can we ever design new diamond cuts without adequate grading tools.

Seriously, how do you go from the Parker-wine-system or hotel-grading to designing both wine or hotels?

Another question: since all systems are brightness-related only, and since we agree them to be rejection-systems only, what does that in all honesty make of the well-meant advice here on PS? I yesterday received a one-page-comment of a consumer on a stone that he had ordered online, but not had in his hands yet. He described the performance of the stone in such detail, something that I find difficult to do even with the stone in hand. Are we on PS possibly guilty (too) of installing a consumer-cut-grade, based on brightness only, giving the impression that it encompasses all aspects of a diamond's cut?

Live long,

I some times wonder about this myself so I think this is a great observation relating to this site specifically.

 

[denverappraiser]

Re: What is the difference between Cut Grading and Cut Rejec

Seriously, how do you go from the Parker-wine-system or hotel-grading to designing both wine or hotels?

Live long,

A few years ago, I had an interesting experience at a hotel in Black Isle Scotland. I stayed at a pleasant little place and ate breakfast with the woman who ran the joint. She was mad as hell because the ratings people (Michelin I think) had just downgraded her from 3 stars to 2. She was clearly expecting this to be a drastic financial blow both in terms of the number of guests expected and the rates she could charge and was parsing their report for what she could do to remedy the situation. It included things like a complaint that the artwork decorating the rooms included images weren't identifiably Scottish. Presumably they wanted sheep, ships, men in kilts, and bagpipes although this wasn't spelled out. Really? The quality of a hotel has to do with whether the inspector liked the art? Apparently it does, and apparently there is no appeal if you get an inspector who doesn’t share your taste. The only solution is to change the art and order a new inspection (at significant cost). I didn’t believe it but she showed me the report. I mention this story because redesigning that hotel to match the standards of the Michelin man for what a Scottish 3star should look like is exactly what she was going to do. She saw no alternative. She needed that rating no matter what it took to get it because her potential guests use those stars as a rejection system. I haven’t been back so I don’t know how it worked out but I’ll bet she did it, I imagine she found some fine pictures of sailing ships or pretty white women to spruce up the place, and I'll bet she got her star. I hope it worked out for her and I certainly wish her all the best.

What does this have to do with diamonds? Maybe nothing, but it has something to do with grading scales and rejection systems and how it affects design.

 

[Rockdiamond]

Re: What is the difference between Cut Grading and Cut Rejec

So many great points being raised.
As a diamond buyer, I've always felt that the scientific assessment of brightness was lacking a reality based component. Is a brighter diamond always "better"?
Put another way, who needs to be a diamond expert if all you need to do is stick to a set of numbers?
Natural response is that cutters need to produce goods that fit into this narrow numerical system...result, loss of diversity.

Thank goodness it's only going on with round diamonds...... I'm seeing a lot of new ideas being tried on Cushion, and radiant cuts- particularly in fancy colors. Lots of cool stuff going on in that regard - precisely due to a lack of standardization.

Instead of travelers seeing a real Scottish room, travelers that stay at the hotel Neil referred to can only see what a stereotypical Scottish room looks like.
I totally get how this relates to the discussion.

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

Seriously, how do you go from the Parker-wine-system or hotel-grading to designing both wine or hotels?

Live long,

A few years ago, I had an interesting experience at a hotel in Black Isle Scotland. I stayed at a pleasant little place and ate breakfast with the woman who ran the joint. She was mad as hell because the ratings people (Michelin I think) had just downgraded her from 3 stars to 2. She was clearly expecting this to be a drastic financial blow both in terms of the number of guests expected and the rates she could charge and was parsing their report for what she could do to remedy the situation. It included things like a complaint that the artwork decorating the rooms included images weren't identifiably Scottish. Presumably they wanted sheep, ships, men in kilts, and bagpipes although this wasn't spelled out. Really? The quality of a hotel has to do with whether the inspector liked the art? Apparently it does, and apparently there is no appeal if you get an inspector who doesn’t share your taste. The only solution is to change the art and order a new inspection (at significant cost). I didn’t believe it but she showed me the report. I mention this story because redesigning that hotel to match the standards of the Michelin man for what a Scottish 3star should look like is exactly what she was going to do. She saw no alternative. She needed that rating no matter what it took to get it because her potential guests use those stars as a rejection system. I haven’t been back so I don’t know how it worked out but I’ll bet she did it, I imagine she found some fine pictures of sailing ships or pretty white women to spruce up the place, and I'll bet she got her star. I hope it worked out for her and I certainly wish her all the best.

What does this have to do with diamonds? Maybe nothing, but it has something to do with grading scales and rejection systems and how it affects design.

Neil,
thanks for good example of problems for business from closed grading system.
I stopped use Michelin guid when Open systems with Consumer grades came .
www.booking.com and tripadvisor is much more useful for me then Michelin guides .

similar system could be part of Cut Performance grade system
Open grading system which account Real consumer experience ( for example you can not publish comments in booking.com if you did not stay this hotel), help a lot for consumers and for good business:
1) If you want open new hotel , you can study in advance that consumers prefer and respect
2) If you do good service for clients then a lot of consumers will know it. If you do something new and your clients like it then you receive very good promotion.

Btw. when I used early Michelin guid I rejected restaurants with 3 stars because dinner in such restaurants is very hard work.
but I was always agree with Michelin Performance restaurant grade. ( 10 years ago)

 

[aljdewey]

Re: What is the difference between Cut Grading and Cut Rejec

I'm sure what I'm about to say will be tantamount to heresy in these here parts, but I'm gonna say it anyway.

In my humble opinion, no grading system will ever be able to truly "standardize" diamonds because each one is unique. This is not like dough where you can just stamp out the forms with a cookie cutter to get identically repeatable cookies. When you're dealing with tone, color, clarity, fire, scintillation, brilliance, etc etc--ALL of which are subjective--there is just no way to standardize that. For what it's worth, I don't really think complete standardization is even important.

For me, the function of a grading report isn't about determining desirability. It's strictly about determining market value, which is based on how the diamond measures against several widely accepted scales of subjective measurement.

The point of a grading system isn't to say that F is 'better' than J; it's really to say that F is less readily available and therefore commands more monetary value than J. Same with clarity; that which is scarcer commands a higher premium.

As a consumer, a grading report instills some level of confidence that I understand the fair market value of my chosen stone. It represents an expert opinion (arrived at through consensus of several experts) as to how the diamond measures against widely accepted (though arbitrary) scales/units of measurement, which in turn sets market value. It's not meant to tell me if I should find the stone beautiful or desirable; it's meant to tell me how to feel confident in its value. To that end, grading labs and grading reports serve a useful purpose.

 

[diagem]

Re: What is the difference between Cut Grading and Cut Rejec

I'm sure what I'm about to say will be tantamount to heresy in these here parts, but I'm gonna say it anyway.

In my humble opinion, no grading system will ever be able to truly "standardize" diamonds because each one is unique. This is not like dough where you can just stamp out the forms with a cookie cutter to get identically repeatable cookies. When you're dealing with tone, color, clarity, fire, scintillation, brilliance, etc etc--ALL of which are subjective--there is just no way to standardize that. For what it's worth, I don't really think complete standardization is even important.

For me, the function of a grading report isn't about determining desirability. It's strictly about determining market value, which is based on how the diamond measures against several widely accepted scales of subjective measurement.

The point of a grading system isn't to say that F is 'better' than J; it's really to say that F is less readily available and therefore commands more monetary value than J. Same with clarity; that which is scarcer commands a higher premium.

As a consumer, a grading report instills some level of confidence that I understand the fair market value of my chosen stone. It represents an expert opinion (arrived at through consensus of several experts) as to how the diamond measures against widely accepted (though arbitrary) scales/units of measurement, which in turn sets market value. It's not meant to tell me if I should find the stone beautiful or desirable; it's meant to tell me how to feel confident in its value. To that end, grading labs and grading reports serve a useful purpose.

Fully agree alj., and would like to add that it doesnt even halt future innovations..., no one can stop natural innovation, not even in an industry this primitive.
True, the top "cut" labs dont take fire, scintilation etc.. that much into consideration during the grading process but they are well aware of its importance. We (cutters) are responsible to take these factors into consideration, then the labs will have no choice but to follow suit.

 

[Draco]

Re: What is the difference between Cut Grading and Cut Rejec

Paul I agree that fire and scintillation are important missing links.

First some information and corrections about AGSL grading practices from one senior lab member(edited for clarity):

Scintillation

"Scintillation is still an active area of research for AGSL. Scintillation is tricky to quantify and even trickier to incorporate into a grading system, therefore the scintillation maps are not used as grading criteria. Generally, a change in a design that increases the average number of scintillation events will simultaneously decrease the average size of the virtual facets. It’s a matter of personal taste which design is better, hence the difficulty in incorporating scintillation maps/metrics in the grading system. "

Dispersion(Fire):

"The Dispersion deduction is calculated in PGS via proprietary methods. For the round brilliant and princess, the dispersion deduction is calculated by analyzing the dispersion in three concentric regions of equal area – the table, inner bezel and outer bezel. A slightly different method is used for the emerald and oval cut grade systems which were developed after the princess and round. "

Brightness

"The brightness deduction is closely related to the quantity of red in the ASET. The ASET image isn’t exactly predictive of the Brightness deduction, as special algorithms are used in PGS to properly account for light that is near the red/blue and red/green boundaries."

"I’d like to point out that PGS does two things (a) Creates an ASET 30 map (b) Creates a “modified” ASET 30 data set. In general, the data set doesn’t exactly correspond with the ASET 30 map, due to the reasons given above. When creating ASET30 bitmaps, the .... performance cut grade is determined from the data set and not the bitmap, so in some (rare) cases the bitmaps can be a little misleading. Consider two hypothetical Sarin scans of two slightly dug out round brilliants. Based on the 1st scan the ray tracer determines that the outer bezel areas are drawing light from 44.9 degrees and therefore paints these areas green (as typical in a dug out stone). Based on the second scan, the same areas are drawing light from 45.1 degrees, so these areas are painted red. Although the ASET image of the second stone would appear to be significantly better than the first, the “modified” ASET 30 data sets would be almost identical, hence the deductions for both stones would be almost identical. .... The main idea is that the ASET colors are “overlapped” near the boundaries to generate a realistic data set for calculating the cut grade."

"Testing during the early phases of research showed that tilting by 15 degrees gives a good indication of how the stone performs when tilted. .... Besides the face-up position, the brightness, dispersion and leakage deductions are also calculated with the stone tilted 15 degrees . Just like the face-up position, the performance of the “tilted” stone must be reasonably close to what’s theoretically possible in order to get a 0 deduction ....The logic is sufficiently general so that several different “flavors” of ideal princess cuts are possible. "

Overall method and goal

"Because the tools enable us to “play” with the grading system ranges/rules and immediately review the results, the process of arriving at the final grading system is very evolutionary in nature. We spend days/weeks debating the relative merits of specific grading ranges and the resulting stones that would be 0s, 1s and so forth. We apply the grading system to real stones to verify it’s reasonableness and double check ourselves. Gradually, we begin to zero in on the final grading ranges and the final grading system emerges. The goal of the process is to develop grading systems that fairly and accurately discriminate the stones into reasonable “grades”, where the ideal stones have the best mix of spread, brightness, dispersion, low leakage and positive contrast possible for the shape"
----------------------------------------------------------------------------------------------------------------------------------------------

My thoughts:

I do have my reservations about some of things included in the AGSL cut grading on Fancy shape outlines. New facet designs(and old) submitted usually by a brand are often the only design for a particular outline shape or facet design that actually receives a cut grade, the rest the "generic" type are only graded for cut if requested. This may make the cut grade more of a marketing tool rather than a mandatory ranking system as in the case of the round brilliant. The cut grading as used in practice today is a form of quality control and strict standard for the brand itself but not a way to compare it to other designs with the same outline shape as it is not mandatory for those to be graded for cut.

The economic reality for the labs is that GIAL which receives the large majority of fancy shapes in North America perceives a potential loss of business if it introduces cut grading for them. AGSL also perceives a loss of potential business so they offer a several types of reports to give the choice whether a fancy should be cut graded or not. A customer viewing a report of a diamond that received an AGS4 cut grade may be deterred from buying it and may opt for a stone with no cut grading at all.

I have to disagree though that there is anything wrong or missing from AGSLs current grading system. They could provide more technical information like % surface area of each size of virtual facet (rough scintillation information), or print their dispersion maps (firemaps) on the report, or provide the breakdown of light performance deductions to provide more information but I am not sure that these would be easy to understand and interpret by the consumer and would not constitute being part of a cut grade. What is missing is the subjective beauty evaluation and this is something that no grading system can include without being dismissed as biased.

 

[Draco]

Re: What is the difference between Cut Grading and Cut Rejec

similar system could be part of Cut Performance grade system
Open grading system which account Real consumer experience ( for example you can not publish comments in booking.com if you did not stay this hotel), help a lot for consumers and for good business:
1) If you want open new hotel , you can study in advance that consumers prefer and respect
2) If you do good service for clients then a lot of consumers will know it. If you do something new and your clients like it then you receive very good promotion.

GIA tried this in their cut grading of rounds. it was an extensive study acceptable by the majority of trade today but judging by the comments on here (especially by niche market consumers and trade) it will never be good enough for some. Subjective grading systems no matter how many data points collected are still just that subjective and will be readily dismissed by those who have a different subjective opinion.

Garry in HCA allows more shallow diamond combinations, GIA study and subsequent cut grading allows more steep deep combinations, both are biased and subjective. Even if either conclusion was reached by polling the majority opinion of a million consumers that opinion may not be relevant to one consumer trying to make a decision on one stone.

I don't think labs should give their subjective opinion to consumers, trade almost always does this, most are always selling whether consciously and intentionally or not.

Objective is fine, present the technical information, provide images and video, explain what it means and then let the consumer make up their own mind and form their own subjective conclusions.

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

re:"Dispersion(Fire):

"The Dispersion deduction is calculated in PGS via proprietary methods."



Fire is not dispersion, Dispersion is not Fire.
Color flashes is result of optical dispersion .

AGS grading system grades cut dispersion instead Fire.

To grade Fire you need know answer at least to below question :

"what is better 2 small color flashes or one big color Flash?"
answer depends from Flashes size , Chroma, space and time flashes distribution . Also answer depends from number other color flashes in same diamond in same time.
There are many other important questions about Fire nature.

Brightness is not Brilliancy.
Brightness + Contrast is not Brilliancy .
Dispersion is not Fire.

 

[Draco]

Re: What is the difference between Cut Grading and Cut Rejec

re:"Dispersion(Fire):

"The Dispersion deduction is calculated in PGS via proprietary methods."



Fire is not dispersion, Dispersion is not Fire.
Color flashes is result of optical dispersion .

AGS grading system grades cut dispersion instead Fire.

To grade Fire you need know answer at least to below question :

"what is better 2 small color flashes or one big color Flash?"
answer depends from Flashes size , Chroma, space and time flashes distribution . Also answer depends from number other color flashes in same diamond in same time.
There are many other important questions about Fire nature.

Brightness is not Brilliancy.
Brightness + Contrast is not Brilliancy .
Dispersion is not Fire.

Serg while I agree with you in part especially if the dispersion maps are not intensity weighted, but I have not seen any peer reviewed articles on this topic by your group and I don't think a debate here is going to carry much impact.

Until your article is published I can only present what AGSL has done and their basis for dispersion and correlation to fire in the grading system can be found in section 5.4 http://www.agslab.com/spie/spie_lo_res.pdf I beleive their method has merit.

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

re:"Dispersion(Fire):

"The Dispersion deduction is calculated in PGS via proprietary methods."



Fire is not dispersion, Dispersion is not Fire.
Color flashes is result of optical dispersion .

AGS grading system grades cut dispersion instead Fire.

To grade Fire you need know answer at least to below question :

"what is better 2 small color flashes or one big color Flash?"
answer depends from Flashes size , Chroma, space and time flashes distribution . Also answer depends from number other color flashes in same diamond in same time.
There are many other important questions about Fire nature.

Brightness is not Brilliancy.
Brightness + Contrast is not Brilliancy .
Dispersion is not Fire.

Serg while I agree with you in part especially if the dispersion maps are not intensity weighted, but I have not seen any peer reviewed articles on this topic by your group and I don't think a debate here is going to carry much impact.

Until your article is published I can only present what AGSL has done and their basis for dispersion and correlation to fire in the grading system can be found in section 5.4 http://www.agslab.com/spie/spie_lo_res.pdf I beleive their method has merit.

Draco,

1) did you read the section 5.4 carefully ?
Authors speak about the Potential to observe Fire.
They did not introduce any Fire metric in article and did not calculate even probability to observe Fire.
They measure just Potential to observe Fire.
"Forward fire maps, produced in the observer’s space, show the potential to observe fire"

AGS PGS software may be grade something similar to Brightness and some Potential of Fire. I respect this work and attempt to create based on 3D model( Btw We introduced this technology in 1999 see for example http://www.gemology.ru/cut/english/document4.htm , http://www.gemology.ru/cut/english/comp/index.htm) because I know very well how is difficult task to create reasonable Brilliancy and Fire metrics ( I am working in this task more than 15 years)
but this all my respect AGS PGS does not grade neither Brilliancy nor Fire.

2) About "Peer Review". There are not enough number of qualify researchers in Light performance field. Magazine redactors have real problem to find independent and qualify specialists for Peer Review our new articles.
3) You may got references about my qualification from GIA or AGS researchers . they well aware about my old works in Light performance.


P/S if you are interesting read articles about Cut Light Performance from different authors then check http://www.octonus.com/oct/projects/

 

[Garry H (Cut Nut)]

Re: What is the difference between Cut Grading and Cut Rejec

re:"Dispersion(Fire):

"The Dispersion deduction is calculated in PGS via proprietary methods."



Fire is not dispersion, Dispersion is not Fire.
Color flashes is result of optical dispersion .

AGS grading system grades cut dispersion instead Fire.

To grade Fire you need know answer at least to below question :

"what is better 2 small color flashes or one big color Flash?"
answer depends from Flashes size , Chroma, space and time flashes distribution . Also answer depends from number other color flashes in same diamond in same time.
There are many other important questions about Fire nature.

Brightness is not Brilliancy.
Brightness + Contrast is not Brilliancy .
Dispersion is not Fire.

Serg while I agree with you in part especially if the dispersion maps are not intensity weighted, but I have not seen any peer reviewed articles on this topic by your group and I don't think a debate here is going to carry much impact.

Until your article is published I can only present what AGSL has done and their basis for dispersion and correlation to fire in the grading system can be found in section 5.4 http://www.agslab.com/spie/spie_lo_res.pdf I beleive their method has merit.

Draco another confounding issue with fire especially, as well as brilliance and scintillation is the fact that we have stereoscopic vision. All the thus published work is monoscopic. I have been using DiamCalc Pro to redo the HCA data for the new HCA app and in many cases I have mono and stereo metrics (with size and intensity weighted options) and I can tell you that there are some considerable differences. I have cross checked the data, because I have a stereo lap top and make 3D movies to check what seem like anomalies. Invariably there seems to be an issue of stones with good brightness washing out fire. (Some here will know I have long thought brightness is the enemy of fire).

But I would like to thank you for your participation. This discussion has been good and I think we may all learn from it (well, everyone except Sergey who already at the forefront of these subjects).

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

re:in many cases I have mono and stereo metrics (with size and intensity weighted options) and I can tell you that there are some considerable differences.

Garry, Draco

Fire Maps( AGS and DCpro) give information only about potential to observe fire( probability to observer Fire if you observe flash. Conditional probability to observe Fire)

Diamonds with Similar Fire maps may have quite different Fire, and via versa .
Information about dispersion of VF's tell nothing about how often you observe any flash( light source) by this VF's
If Potential of Fire big it does not mean that Fire is big
If Potential of Fire low then Fire is low
So it is rejection tool to reject diamonds with very low dispersion . this tool can not compare Fire for 2 diamonds if difference in dispersion is not huge for these diamonds. of course if you compare 2 diamonds with similar optical pass( with similar probability to see flashes) then difference in dispersion become important to compare .
soo you can receive rough comparison just for similar diamonds ( for example around C41P34.5) or for diamonds with big difference in dispersion. just it.

 

[Karl_K]

Re: What is the difference between Cut Grading and Cut Rejec

Frankly I don't think there ever will be a grading system that accurately grades scintillation and or fire.

There are some very serious flaws in the current systems that attempt to measure and grade brightness and it is an easier problem by many orders of magnitude.
The head shadow/obstruction models are very badly done/broke in both the GIA observation studies and AGS ASET studies. The IS has the same flaw as ASET, unrealistic obstruction.
That does not make the research/grade/tools useless it just has to be taken into account and other supporting information gathered and weighed. Then the final decision is made by the owner in their own environment over time.

Then you get to how the grades are applied using scans.. garbage in/garbage out is a very serious problem.

 

[Serg]

Re: What is the difference between Cut Grading and Cut Rejec

Frankly I don't think there ever will be a grading system that accurately grades scintillation and or fire.

There are some very serious flaws in the current systems that attempt to measure and grade brightness and it is an easier problem by many orders of magnitude.
The head shadow/obstruction models are very badly done/broke in both the GIA observation studies and AGS ASET studies. The IS has the same flaw as ASET, unrealistic obstruction.
That does not make the research/grade/tools useless it just has to be taken into account and other supporting information gathered and weighed. Then the final decision is made by the owner in their own environment over time.

Then you get to how the grades are applied using scans.. garbage in/garbage out is a very serious problem.

Karl ,
Brilliancy is most difficult for grade. Fire is much more simple phenomena than Brilliancy .
Firstly we will see Score systems for Fire, Scintillation then after many years later for Brilliancy .

 

[Paul-Antwerp]

Re: What is the difference between Cut Grading and Cut Rejec

 

[Draco]

Re: What is the difference between Cut Grading and Cut Rejec

re:in many cases I have mono and stereo metrics (with size and intensity weighted options) and I can tell you that there are some considerable differences.

Garry, Draco

Fire Maps( AGS and DCpro) give information only about potential to observe fire( probability to observer Fire if you observe flash. Conditional probability to observe Fire)

Diamonds with Similar Fire maps may have quite different Fire, and via versa .
Information about dispersion of VF's tell nothing about how often you observe any flash( light source) by this VF's
If Potential of Fire big it does not mean that Fire is big
If Potential of Fire low then Fire is low
So it is rejection tool to reject diamonds with very low dispersion . this tool can not compare Fire for 2 diamonds if difference in dispersion is not huge for these diamonds. of course if you compare 2 diamonds with similar optical pass( with similar probability to see flashes) then difference in dispersion become important to compare .
soo you can receive rough comparison just for similar diamonds ( for example around C41P34.5) or for diamonds with big difference in dispersion. just it.

Serg,

1) You haven't explained or even defended your model. If you have show me the published article, or poster presentation if not in a journal on your web site! Nothing related to this in the last 10 years in your cut study link.

I mean the details the data and the references to previous work that you built upon.

2) In Diamcalc you switched from:

Chromatic Disperision Statistics Diagram
Intensity Weighted Statisitics Diagram

in an earlier beta.

and now they are

Dispersion Statistics Diagram (loose diamond)
Dispersion Statistics Diagram (in a ring)

Define how you calculate these diagrams.
Define how the are changed.
Define how they are supposed to be used.

Define something there is no explanation on anything!