Fyi: IGI Scores Diamonds for Light Performance
- Thread starter Mlh
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0515vision
Brilliant_Rock
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Wow! How soon will these certificates start circulating? Excited to see how they correlate.
Part of my brain says, snatch up non branded great cuts now!
Part of my brain says, snatch up non branded great cuts now!
gatorsrule
Rough_Rock
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I have a feeling the light performance scores are based on the specs of the diamond and not really based on someone looking at the diamond through an optical scope.
gatorsrule
Rough_Rock
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Scores with a computer generated ideal scope based on the data. Maybe better than HCA?
Would be really useful if retail expose that data to enable effective filters to reduce the legwork of finding diamonds that have specific qualities buyers are after.
Hearts and arrows, HPHT, CVD aren't always available as filters for example.
Would be really useful if retail expose that data to enable effective filters to reduce the legwork of finding diamonds that have specific qualities buyers are after.
Hearts and arrows, HPHT, CVD aren't always available as filters for example.
I found the following "Score Card" on the IGI website during my research for a perfect stone this week:
It seems that the evaluation of the light performance is mainly based on the proportions. A pricescope ideal diamond would be the perfect IGI light score near to 100.
Edit:
Here are some additional information:
„Note that light performance analysis is based on external proportions and does not account for dense clarity characteristics/reduced transparency.“
„The Ideal-Scope Representation, generated with ray-tracing software, conforms to the diamond’s specific parametric averages“
In other words: The averaged proportions are used in a software that simulates the reflections.
It seems that the evaluation of the light performance is mainly based on the proportions. A pricescope ideal diamond would be the perfect IGI light score near to 100.
Edit:
Here are some additional information:
„Note that light performance analysis is based on external proportions and does not account for dense clarity characteristics/reduced transparency.“
„The Ideal-Scope Representation, generated with ray-tracing software, conforms to the diamond’s specific parametric averages“
In other words: The averaged proportions are used in a software that simulates the reflections.
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Ok I've used their charts to get a grading for a diamond I have and previously scored with HCA and the IGI scoring is fairly relaxed compared to the tougher standards of HCA
With IGI
Light performance = Exceptional
Brightness = Exceptional
Fire = Exceptional
Contrast = Exceptional
With the higher standard HCA
(Only an average Cut Advisor Score of 2.1)
Light return = Very good
Fire = Very good
Scintillation = Very good
Spread = Very good
So it seems that IGI may not be that stringent.
With IGI
Light performance = Exceptional
Brightness = Exceptional
Fire = Exceptional
Contrast = Exceptional
With the higher standard HCA
(Only an average Cut Advisor Score of 2.1)
Light return = Very good
Fire = Very good
Scintillation = Very good
Spread = Very good
So it seems that IGI may not be that stringent.
0515vision
Brilliant_Rock
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What are the stats in the diamond you scored? Mind sharing?
Having taken another look at all the 16 pages of the table percentages in the IGI doc it's physically impossible to come out with a low score on their scales. The lowest is Superior, and the only other grade available is Exceptional.
Although there are 3 lower categories available, the scoring doesn't provide low enough numbers to categorise a diamond into that bucket. (Even if fudging a bad result). So the only grades that can be assigned are in CAPS below it seems. IGI don't provide any score lower than 90 for any category in any of the tables. Any cut beyond these boundaries are not provided a low score to be able to ascertain a low rating. (Unless I have misinterpreted)
Low
Moderate
High
SUPERIOR
EXCEPTIONAL
This is the diamond rated under both scoring systems https://www.igi.org/verify-your-report/?r=LG618455187
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Howdy everyone,
More info here:
and here:
I am sure there are a million and one questions.
If anyone was curious about what was taking a lot of my PS time
I am not an official spokesperson so any information is not official.
I was one of many working on it, John Pollard and I did most of the system design work with support from many people.
To answer some questions,
At this launch reports are only issued, optionally, for the “Exceptional” range. Will expand to Superior next.
We have a ton of respect for Garry and the HCA in the end we found out we agreed with the HCA much of the time but in some cases we disagreed.
We do take more parameters into consideration, such as lower girdle/halve angles and upper girdle/halve angles this changes the edges a lot.
Garry was instrumental in training both John and myself as well as many others.
I still learn something from him nearly every time we talk even after all these years.
More info here:
and here:
I am sure there are a million and one questions.
If anyone was curious about what was taking a lot of my PS time
I am not an official spokesperson so any information is not official.
I was one of many working on it, John Pollard and I did most of the system design work with support from many people.
To answer some questions,
At this launch reports are only issued, optionally, for the “Exceptional” range. Will expand to Superior next.
We have a ton of respect for Garry and the HCA in the end we found out we agreed with the HCA much of the time but in some cases we disagreed.
We do take more parameters into consideration, such as lower girdle/halve angles and upper girdle/halve angles this changes the edges a lot.
Garry was instrumental in training both John and myself as well as many others.
I still learn something from him nearly every time we talk even after all these years.
- Joined
- Aug 4, 2008
- Messages
- 14,772
As long as it has reasonable lowers and stars% the combination looks like a winner to me.
More info here:
and here:
I am sure there are a million and one questions.
If anyone was curious about what was taking a lot of my PS time
I am not an official spokesperson so any information is not official.
I was one of many working on it, John Pollard and I did most of the system design work with support from many people.
To answer some questions,
At this launch reports are only issued, optionally, for the “Exceptional” range. Will expand to Superior next.
We have a ton of respect for Garry and the HCA in the end we found out we agreed with the HCA much of the time but in some cases we disagreed.
We do take more parameters into consideration, such as lower girdle/halve angles and upper girdle/halve angles this changes the edges a lot.
Garry was instrumental in training both John and myself as well as many others.
I still learn something from him nearly every time we talk even after all these years.
Thanks for the info! Do you know if IGI plans to update old IGI reports, or will only the new ones include the light performance info?
Howdy everyone,
More info here:
and here:
I am sure there are a million and one questions.
If anyone was curious about what was taking a lot of my PS time
I am not an official spokesperson so any information is not official.
I was one of many working on it, John Pollard and I did most of the system design work with support from many people.
To answer some questions,
At this launch reports are only issued, optionally, for the “Exceptional” range. Will expand to Superior next.
We have a ton of respect for Garry and the HCA in the end we found out we agreed with the HCA much of the time but in some cases we disagreed.
We do take more parameters into consideration, such as lower girdle/halve angles and upper girdle/halve angles this changes the edges a lot.
Garry was instrumental in training both John and myself as well as many others.
I still learn something from him nearly every time we talk even after all these years.
Ah, thanks for sharing! The blank squares in the scoring matrix would explain the fact the system is yet to be expanded out.
As long as it has reasonable lowers and stars% the combination looks like a winner to me.
Is this image generated from the diamond report numbers?
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Thanks for the clarification. How would I generate an image from numbers, or is that the preserve of special access?
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The software to do so is no longer for sale.
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I posted here about a webinar that is on Rapaport next week with John Pollard and me:
IGI Webinar John Pollard & Garry Holloway
This webinar is on Rapaport next week - if you dont want to watch it live - you can register and they will send you the youtube link later: https://www.linkedin.com/events/seeingthelight-allyouneedtoknow7193225976388943873/theater/ There is also a discussion on the Lab Grown forum where Karl...
www.pricescope.com
Ok.
The other diamond I bought
With the IGI scoring
Light performance = Exceptional
Brightness = Exceptional
Fire = Exceptional
Contrast = Exceptional
and with HCA
Cut Advisor Score of 1.5
Light return = Excellent
Fire = Very good
Scintillation = Very good
Spread = Very good
Would it be possible to see the computer generated image from the IGI PDF report figures for this diamond too, if easy, and if you have time
Thanks.
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Its not going to show much as the base combo works very well.
Do you have a spin video link so I can estimate the other values not on the report?
0515vision
Brilliant_Rock
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This is the video
Loupe360
loupe360.com
That’s a pretty diamond!
We usually tell people to use HCA as an exclusion tool and not to split hairs too much with it. Granted, we also tell ppl that a crown height of 14 isn’t necessarily going to give “exceptional” fire.
Will be interesting to hear what the experts say.
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That's one of the things commonly passed around that is false.
Many of the combinations with slightly lower CH do favor brightness over fire across a wide range of lighting.
However it is 100% false that in lighting conductive to fire that they can't knock your socks off as much as any other combo.
Edit: im not at my pc to create an image but its not going to show much, the combo works.
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0515vision
Brilliant_Rock
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Good to know!
Lately, there have been a lot of 15.5-16 crown heights touted as great for fire. But according to you, those combo need to have longer lowers, is that correct?
Just trying to get my details straight, and as always, really appreciate your input here on PS!
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Depends on the exact combo.
A high CH can be from a small table or a steep CA or some combo of both.
What they need to work the best varies a lot depending on specifics.
40.6PA and lower, longer lgf% = less obstruction area
Over 40.6PA with steeper crowns, longer lgf% = less chance of leakage.
Longer in this case means 77+
For many combos 77-78% is a nice balance point.
When you get further out 80% is needed to expand the edges of acceptable combos.
If you have IS/ASET scopes you can use them instead of the general rules to set the edges.
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