How do you calculate EC cut grade?

[Wholovesskunks]

Sarin Report! So according to the tool, with the crown height % being 12.64% it comes out to 1A. At least if I did it correctly. Someone correct me if I'm wrong.

 

[BlingDreams]

Sarin Report! So according to the tool, with the crown height % being 12.64% it comes out to 1A. At least if I did it correctly. Someone correct me if I'm wrong.

What did the Sarin report say about its Brightness, Fire, and Scintillation? There should be a graph showing where they rank. Here's an example:

 

[Wholovesskunks]

That's all they sent me. :/

 

[MollyMalone]

What did the Sarin report say about its Brightness, Fire, and Scintillation? There should be a graph showing where they rank. Here's an example:

Shiny, that graph was generated by OGI's FireTrace, it's not a Sarin product. (IIRC our Trade members aren't big fans of FireTrace.). What B2C sent to Wholovesskunks is the Advanced Manufacturers Sarin Report, which gives her all the facet info.

 

[BlingDreams]

Shiny, that graph was generated by OGI's FireTrace, it's not a Sarin product. (IIRC our Trade members aren't big fans of FireTrace.). What B2C sent to Wholovesskunks is the Advanced Manufacturers Sarin Report, which gives her all the facet info.

Interesting. That one is from IDJewelry, who of course is highly respected on here and I believe is also a trade member? It was done in conjunction with the Sarin report.

I wonder if the OGI product is in competition with the Sarin Dimension product that gives the information on light performance.

 

[Wholovesskunks]

Can we tell anything additional by this advanced report they sent me?

 

[MollyMalone]

Shiny, that graph was generated by OGI's FireTrace, it's not a Sarin product. (IIRC our Trade members aren't big fans of FireTrace.). What B2C sent to Wholovesskunks is the Advanced Manufacturers Sarin Report, which gives her all the facet info.

Interesting. That one is from IDJewelry, who of course is highly respected on here and I believe is also a trade member? It was done in conjunction with the Sarin report. * * *

Sorry I didn't type out a more complete, more accurate comment previously, but my phone had just rung & I wanted to finish typing before getting into that "deep" phone conversation. My recollection is that John Pollard (formerly with Whiteflash, now the US Executive for Crafted by Infinitiy) and Rhino (Jonathan Weingarten of Good Old Gold) expressed the view that OGI hadn't demonstrated to them that the underlying algorithms of FireTrace yielded a particularly meaningful end product & they "dinged" FireTrace especially on its Scintillation scoring. I also seem to remember some Trade members of PS, not just us ordinary PSers, commenting that FireTrace (like the AGA-NAJA Cut Grading tool) isn't so useful for emerald cuts.

Can we tell anything additional by this advanced report they sent me?

I would swear that Karl K., who posted upthread, had written a nice tutorial on how to make use of all the pavilion info, if you've been given that, re emerald cuts. But darned if I can find it now. Perhaps he will return to this thread & point us in the right direction on that

 

[Wholovesskunks]

I've been hoping he or someone could give us more insight.

 

[Karl_K]

Here is the link to my article about step cut pavilions.
https://www.pricescope.com/journal/performance-and-p3-facets-discussion-about-step-cut-diamonds
I should have discussed leakage other than critical angle leakage more.
A lot of bad p3 angles are below the critical angle but not all of them.
Most of the leakage in diamonds is not leakage like a window it is parts of the diamond drawing light from the pavilion and returning it towards the viewer instead of drawing light from the top.
These can be well above the critical angle.

The report doesn't help a lot.
The placement of the facet rows is just as important as the angles and that information is lacking.
2 step cuts with the exact same angles can look totally different from each other if the facet row placement, corners, l/w ration or table size is even sightly different.

 

[Karl_K]

The question I always ask myself when viewing an ASET image is if the ratio of red and green compared to white and blue enough to make it a bright diamond.
Generally large areas of white are not desirable.

 

[Wholovesskunks]

Weird thing is I pulled a bunch of the blueprints on excellent cut emerald's from B2C and so many were similar to mine. Guess I'll just have to cross my fingers!

 

[Rockdiamond]

Hi Everyone!
Static ASET images on an emerald cut don't provide enough meaningful information to be useful.
Same for the light performance graphs on OGI, or Sarin. Both of which can be calibrated to completely change the results.
As Karl has pointed out, knowing exact facet placement and angles would be crucial.
However, my opinion is that such info still won;t help emerald cut shoppers.
Just having the correct crown height does not mean the stone will be a winner. I have purchased literally thousands of emerald cuts. Many simply "break the mold" and possess remarkable performance with things like lower crown heights etc.
I respect David Atlas, but the cut grade charts are misleading- which makes them worse than useless.
Wholovesskunks- my advice is to stop stressing and wait till the diamond comes. Your eyes will tell you what you need to know.

 

[whitewave]

I agree just wait. I bought my asscher blind (lol) and I have been completely obsessed with it for 5 years now.

Sometimes you luck out

 

[Wholovesskunks]

Can we tell by the video if its decent?

 

[ChristineRose]

Kind of a thread hijack, but what do the experts think of GCAL for an emerald cut? I can't find anyone even using GCAL for an emerald, but it seems like they should be the lab of choice.

 

[Rockdiamond]

Can we tell by the video if its decent?

my personal opinion on rotating videos is that they give not enough info, and too much info at the same time.
You can't actually rock the stone and you look at 50% of the spin in a way you'd never look at a diamond in real life.
But still, you can get the idea of the overall personality.
Most important wholovesskunks: Even if we had 10 PS members looking at the stone in person, we're not going to have 10 people feeling the same way.
Is square better or rectangular? If it's rectangular, how rectangular is best? 1.3:1 ? 1.4:1?
Fancy shapes can have so much variance from stone to stone in elemental aspects such as the overall shape that there's simply no "right" answer.
Yes, if we have a really bad example, it's likely we'd get closer to a consensus ( negative). But at the other end- in stones that are well cut- there's going to be a wide swath of opinions.

 

[Rockdiamond]

Kind of a thread hijack, but what do the experts think of GCAL for an emerald cut? I can't find anyone even using GCAL for an emerald, but it seems like they should be the lab of choice.

You've definitely peaked my curiosity. Why would you feel that GCAL would be the lab of choice for EC's. I'm genuinely interested- there's no info on their site

 

[Wholovesskunks]

Would you say it's brown or yellow tone? I'm trying to choose the color of my setting. White gold vs yellow.

 

[Wholovesskunks]

I definitely like the 1.35 ratio. I struggle too. I wish we had local vendors that carried a good amount of ECs. Sadly we don't. :/

 

[ChristineRose]

You've definitely peaked my curiosity. Why would you feel that GCAL would be the lab of choice for EC's. I'm genuinely interested- there's no info on their site

Because they have the brilliance analysis and a light performance grade which as far as I can tell isn't a chart based grade like GIA, or a point based grade like AGS, but rather some sort of ray tracing based on actual measured facets.

If I'm right, then they should be able to generate light performance data about any fancy cut without the "you have to see it" problem. Not that brilliance, symmetry, and light return are the only things that go into beauty, but the other factors tend to be easier to grasp from a report.

 

[oldminer]

Use of just the un-automated AGA Cut Grade charts can be misleading, as Rockdiamond has told you. However, using the automatic grader takes the guesswork out of how to interpret the data to the extent that many diamonds which fail to be well cut are eliminated and better cut diamonds are generally better rated. It is not a 100% event, but we are talking about a screening tool, not "the way to choose a diamond".

The scientific tools that can be used to calculate or measure light performance also have limitations. Not only can many be mis-calibrated by accident or by intent, but they only "measure" limited data and do not tell the entire story of a diamond. NOTHING DOES THAT better than a skilled human's eyes at the present time. The judgment of beauty is subjective and while people may tend to agree about some elements of beauty, there is no objective way to determine for everyone which single appearance is "best". We are doing well with shapes like rounds, princess and a couple others, but we are not close with emerald cuts to the same extent.

When a diamond scores well with the AGA grader, meaning 2B or better for fancy shapes, there is a good chance you are on the path to a nicely cut and also pleasing appearance stone. When a diamond scores 3A or lower, there are good reasons to keep looking for another choice. As long as you buy aware of the issues, you won't end up surprised or disappointed later. I think that makes the AGA Grader very useful and fair, but there are those who disagree and have been saying so for many years. Meanwhile the science oriented guys of the Internet are doing better and the traditionalists are struggling to hold their ground more and more. I hope I get to see the newest technologies employed to bring openness and fairness to the diamond business.

 

[Rockdiamond]

The issue is that any static measurement of light performance is worse than meaningless, as it gives a false sense of security, and will eliminate stones that might be far better in terms of real life light performance and how a given individual perceives it.
There's simply no way to quantify a fancy shape- emerald cut in particular- in a meaningful way, on a report.

There's certainly no broad industry agreement on fancy shape light performance in general- but the greatest possibility of finding any consensus would be AGSL.
GCAL is a non issue at least as far as in the trade from my perspective.
Are there vendors promoting GCAL?

 

[oldminer]

Would you agree that having an extremely thin girdle is not as durable for a long term purchase as having a diamond with a medium girdle? Would you agree that a diamond with a 63% depth will have substantially more visible face-up size appearance than a very similar weight diamond of the same general length to width ratio with a 73% depth? Would you believe that a princess cut diamond with a shallow crown height of 4% will create less face-up dispersion and scintillation from the crown area as a similar outline diamond with a 12% crown height? These are things that are factual differences, not subjective opinions. You can make some important distinctions about the durability, finish and visual size of fancy shape diamonds of similar shapes and weights which will have an important impact on informed decision making. These are not the sole examples of what screening tools can do even when few decisions should be based on them alone.

Admittedly, one must leave fancy color diamonds out of the discussion about standardized cutting because getting the color to face-up at is best remains, for now, primarily an art and for highly specialized clientele.

 

[Karl_K]

Ok I will bite!

Would you agree that having an extremely thin girdle is not as durable for a long term purchase as having a diamond with a medium girdle? Yes, in my opinion Would you agree that a diamond with a 63% depth will have substantially more visible face-up size appearance than a very similar weight diamond of the same general length to width ratio with a 73% depth? With step cuts that is not a given the 73% depth can have larger spread and with a higher crown a larger 3d appearance. Would you believe that a princess cut diamond with a shallow crown height of 4% will create less face-up dispersion and scintillation from the crown area as a similar outline diamond with a 12% crown height? No, a 4% CH princess with well matched pavilion can out perform one in every way with a 12% crown and a poorly matched pavilion. These are things that are factual differences, not subjective opinions. They are not facts at all they are your opinions. You can make some important distinctions about the durability, finish and visual size of fancy shape diamonds of similar shapes and weights which will have an important impact on informed decision making. These are not the sole examples of what screening tools can do even when few decisions should be based on them alone.
No decisions should be made based on any one tool.

Admittedly, one must leave fancy color diamonds out of the discussion about standardized cutting because getting the color to face-up at is best remains, for now, primarily an art and for highly specialized clientele.

 

[Karl_K]

my personal opinion on rotating videos is that they give not enough info, and too much info at the same time.
You can't actually rock the stone and you look at 50% of the spin in a way you'd never look at a diamond in real life.
But still, you can get the idea of the overall personality.
Most important wholovesskunks: Even if we had 10 PS members looking at the stone in person, we're not going to have 10 people feeling the same way.
Is square better or rectangular? If it's rectangular, how rectangular is best? 1.3:1 ? 1.4:1?
Fancy shapes can have so much variance from stone to stone in elemental aspects such as the overall shape that there's simply no "right" answer.
Yes, if we have a really bad example, it's likely we'd get closer to a consensus ( negative). But at the other end- in stones that are well cut- there's going to be a wide swath of opinions.

I agree with David given well cut stones there will be a wide range of looks and personalities that one person may like and some one else not like with fancy cuts.

 

[Karl_K]

GCAL is a non issue at least as far as in the trade from my perspective.
Are there vendors promoting GCAL?

Yea there are some, Blue Nile being the biggest.
Having reverse engineered the tests I am not impressed at all that they are very useful.

 

[oldminer]

Karl, your conditions where you disagree are far out. That's why the tool is for SCREENING, not for final selection. I never saw a 4% crown height princess which could compete with a better cut princess with a decent crown height, but maybe in theory one could produce such a stone. The shallow crown angle result would likely be a durability issue and what about weight retention. Is your example a viable commercial reality or a computerized hypothetical with no market reality?

The example for the visual size, I used a simple visual size which is the area inside the outline of the diamond face up. It is what consumers understand. You pull out a "3D" area to refute my opinion of fact. That is pure is computer geek stuff and not usable data for marketing or consumer understanding.

Thanks for your one agreement about girdle thickness. That was a hard won point, but always glad to see the argument can be made and understood. No one should use the tool blindly for selection, but within the realm of commercially available diamonds, I believe the automated grader can be useful in screening. What other screening tools do we have? ASET, I-S and several other more complex things exist. None of them tell the entire story. Some do light behavior nicely, mine does some good thing with durability, visual size and finish details the others may not cover so well.

Thanks for giving a thoughtful and good counter-point response.

 

[Rockdiamond]

snip..... Meanwhile the science oriented guys of the Internet are doing better and the traditionalists are struggling to hold their ground more and more. I hope I get to see the newest technologies employed to bring openness and fairness to the diamond business.

Hi Dave!
First and foremost, I'm thrilled to have an open and respectful dialog on this longstanding debate.
It is difficult for me to critique something you worked so hard on without feeling like I'm somehow "
dissing" you. But we do have very differing perspective, hopefully illuminating for readers. We were posting at the same time yesterday so I'll answer each post separately.
About that part in bold: There's little doubt that diamond sales are deserting B&M retail jewelers. Also true that many of those same B&M's scoff at the technology we're discussing. And do so out of hand, without taking the time to really look at the technologies. I used to be in that group, but I've learned so much in my participation here. I still feel the technologies are not all that useful to consumers, but now I understand the technologies- and why they appeal to a segment of shoppers.
About that part in bold from my perspective it's not diamond technology changing the internet playing field as much as internet technology, and money.
On our site, we stress the human aspects of diamonds and are doing quite well thank you. But we've been selling diamonds online since 1999.
Try to get a footprint today, and the starting price is in the millions- and not for diamonds, or ASET's Sarins etc. It's for things like website design, SEO, and Adwords. So it's not diamond technology changing this segment. In fact, we find that there's a massive percentage of shoppers who really don't like the technology, as compared to "hands on" assessment. But we agree on that part I think.

 

[oldminer]

Rockdiamond;

I know you are not dissing me and that we definitely come at this with different perspectives. I begun more of less where you began, but my path and learning interests led me down technology pathways with early familiarization with the Internet and into machine diamond grading with a tech company. Business guys have taken the open opportunity provided by the Internet to change the sales of diamonds in huge ways. I saw this coming like a freight train early on and was tremendously impressed with the innovations in sales approaches that several Pricescope vendors are justly famous for offering consumers. Consumers clamored for more details, data and information, and technologically adept vendors have spent a fortune on making it happen. You can't be an effective diamond seller from a pushcart or an exchange counter these days in most places unless you sell the truly unique and collectible items that you offer. You may be one of the luckiest dealers around because you still can look at a diamond that is truly unique and decide that it is lovely and worth the money or not pretty or intensely colored enough to be the one you want to put into inventory. The judgment of beauty is the art of the business. The Internet fosters the successful marketing of more commodity oriented diamonds which can be engineered, duplicated, photographed ten different ways and sold in a competitive way via search engines. Much more standardization of such stones is useful and we certainly have a lot of standards that can be analyzed, concocted and hyped.

Essentially, dealers all compete for sales to consumers who have access to as much or more information as they can possibly utilize. We still are not at the end game, of course. Many fancy shapes remain with only vague standards, but surely, the powers that be will do their best to make categories and classes for every commercially produced shape in the next few years. What I did was to try to categorize diamond grading, from visual observation and practical experience, in an age before this technological period and before the arrival of the business side of the Internet. When the most up to date tools become available for fancy cut grading, I'd expect what I compiled from 1985 to 2002 in the automated cut grader tool to mix well with the more scientific results I know are on the way to the industry. It won't be long until all the shapes have cut standards and all the high tech vendors of non-fancy color diamonds will be using this data and technology to make better and more rapid sales to happier customers who have increased knowledge and confidence.

I see this as a win for the diamond business as well as consumers. I also understand that such a large and rapid change in methodology is highly upsetting to those who thought things were good enough in 1975.....and they were great back then...

 

[Rockdiamond]

Thank you Dave- we are surely both lucky guys
About the second post of yesterday. I'm going to tackle the very first point because it's elemental the overall discussion.

Would you agree that having an extremely thin girdle is not as durable for a long term purchase as having a diamond with a medium girdle? snip....

No, I can't agree that simply having an extremely thin girdle noted on a GIA report equates to a surety of durability concerns.
The reason is that fancy shape diamonds have different sort of girdle considerations as compared to a round diamond.
An emerald cut, for example, has eight separate, and individual girdles.
Therefore a larger variation from thick to thin is acceptable.
Regarding durability and EX THIN girdles: assessment depends on how where and other specifics.
We keep close ties with many of our clients- and will learn of damage.
Center diamond breakage is extremely rare, regardless of girdle.
For these reasons, I do not automatically eliminate candidates due to EX thin girdle noted on a GIA report.

I am a very lucky dealer. I get to look at thousands of diamonds a month in the flesh.
Of course, that puts me in a different position as compared to a consumer, who can't look at the stones in the flesh.
But the lessons learned through my experience tell me that elimination based on a factor like EX thin Girdle will cull some of the most desirable emerald cuts.
To use an analogy- it's like saying anyone 6ft is automatically a better baskeball player than a 5'11" candidate for that reason alone. Any elimination device that culls too much can be worse than one that does not cull at all because it can eliminate the very best candidate- and the field is limited.
In fact, if we're considering Emerald Cuts specifically, the field is extremely limited given the wide variety of color, clarity, ct weight cost AND proportions.
Say a guy is looking for an H/VS1 2ct with 1.25:1 proportions- it's not like that they're falling off trees