shape
carat
color
clarity

AGS Ideal performance, poor HCA; a bit confused.

dumbo

Shiny_Rock
Premium
Joined
Jan 5, 2015
Messages
221
Looking at several diamonds, I noticed that the AGS Ideal light rated diamonds are often scoring fairly poor on the HCA scale. Is the HCA just an estimate? One I looked at had a 2.8 score, another a 3.7. Does that mean the AGS Ideal light performance rating is weaker than the HCA elimination tool? Or that the HCA is just an estimate, a good way to weed out poor performers, but also a tool that lets strong performers get eliminated unnecessarily?

Of course, there are still plenty of AGS ideal diamonds that score under a 2, but being the AGS ideal rating is fairly strict, I would have guessed it was pretty much 100% scoring at or under 2. Please explain, it is a bit confusing!
 

luvdajules

Brilliant_Rock
Joined
Mar 24, 2014
Messages
539
Hi OP, this comes up regularly as a question. HCA is a rejection tool to help eliminate stones with bad ca/pa combos (hca is a calculation based off 4 values from a diamond that has many, many more contributions). So, yes, some good stones will be rejected (stones that have uncomplimentary ca/pa but have been designed to compensate overall). Also, some people are willing to go up to hca of 2.5 without sacrificing too much performance if the price is right and reflector images are good.

How did the 2.8 hca diamond look to you? did you get an IS or ASET?
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,760
dumbo|1425279698|3840603 said:
Looking at several diamonds, I noticed that the AGS Ideal light rated diamonds are often scoring fairly poor on the HCA scale. Is the HCA just an estimate? One I looked at had a 2.8 score, another a 3.7. Does that mean the AGS Ideal light performance rating is weaker than the HCA elimination tool? Or that the HCA is just an estimate, a good way to weed out poor performers, but also a tool that lets strong performers get eliminated unnecessarily?

Of course, there are still plenty of AGS ideal diamonds that score under a 2, but being the AGS ideal rating is fairly strict, I would have guessed it was pretty much 100% scoring at or under 2. Please explain, it is a bit confusing!
Yes, the HCA is just an estimate. It's not looking at the actual diamond. It's input includes only a few rounded and averaged data points and compares them to pre-defined tables that indicate likely performance.

The AGS light performance system looks at the 3D model of the actual diamond and calculates the contribution of every facet to overall light performance through a powerful ray tracing engine.
 

MelisendeDiamonds

Shiny_Rock
Trade
Joined
Jul 2, 2014
Messages
234
dumbo|1425279698|3840603 said:
Looking at several diamonds, I noticed that the AGS Ideal light rated diamonds are often scoring fairly poor on the HCA scale. Is the HCA just an estimate? One I looked at had a 2.8 score, another a 3.7. Does that mean the AGS Ideal light performance rating is weaker than the HCA elimination tool? Or that the HCA is just an estimate, a good way to weed out poor performers, but also a tool that lets strong performers get eliminated unnecessarily?

Of course, there are still plenty of AGS ideal diamonds that score under a 2, but being the AGS ideal rating is fairly strict, I would have guessed it was pretty much 100% scoring at or under 2. Please explain, it is a bit confusing!

The AGSL ray tracing system is far superior to HCA it takes into account all facets from an actual scan. HCA is a rejection tool and a flawed one at that due to the limited inputs of averaged and rounded measurements. The author or HCA prefers shallow combinations and penalizes deeper combinations putting more emphasis on spread considerations as such it has a bias which is not found in the more objective AGSL system.

Despite this the two systems should have good agreement in the middle of their ranges, on some borders they differ but those are marginal choices and difficult to select without inspecting the stones in hand on a case by case.

One guess to explain your observations is that If the ones you are considering are AGS 0000 but primarily score higher on HCA I'd say you are probably sacrificing cut to fit a particular budget and if thats the case I'd probably stick to GIA graded XXX stones instead and not pay the premium for the borderline AGS 0000 stones.
 

dumbo

Shiny_Rock
Premium
Joined
Jan 5, 2015
Messages
221
MelisendeDiamonds|1425311767|3840722 said:
dumbo|1425279698|3840603 said:
Looking at several diamonds, I noticed that the AGS Ideal light rated diamonds are often scoring fairly poor on the HCA scale. Is the HCA just an estimate? One I looked at had a 2.8 score, another a 3.7. Does that mean the AGS Ideal light performance rating is weaker than the HCA elimination tool? Or that the HCA is just an estimate, a good way to weed out poor performers, but also a tool that lets strong performers get eliminated unnecessarily?

Of course, there are still plenty of AGS ideal diamonds that score under a 2, but being the AGS ideal rating is fairly strict, I would have guessed it was pretty much 100% scoring at or under 2. Please explain, it is a bit confusing!

The AGSL ray tracing system is far superior to HCA it takes into account all facets from an actual scan. HCA is a rejection tool and a flawed one at that due to the limited inputs of averaged and rounded measurements. The author or HCA prefers shallow combinations and penalizes deeper combinations putting more emphasis on spread considerations as such it has a bias which is not found in the more objective AGSL system.

Despite this the two systems should have good agreement in the middle of their ranges, on some borders they differ but those are marginal choices and difficult to select without inspecting the stones in hand on a case by case.

One guess to explain your observations is that If the ones you are considering are AGS 0000 but primarily score higher on HCA I'd say you are probably sacrificing cut to fit a particular budget and if thats the case I'd probably stick to GIA graded XXX stones instead and not pay the premium for the borderline AGS 0000 stones.

Thanks. Actually, the ones I was considering were all AGS 000 (to weed out under performers) but they all scored kinda high (poorly) on HCA (you had said high, assuming you meant a high number, not a good score). One had a 36.5 crown and pavilion, another a 34.8 crown and 41.1 pavilion, both were 62/55 otherwise. My understanding initially was that an AGS 000 diamond is a guaranteed good performer. You are right though, these are selling at perhaps a $1000 premium for 2ct, not the $4000 premium that a super ideal commands.

Unfortunately, the vendor, while very helpful and PS approved, does not have an idealscope. The AGS document also does not have a light map. Which could be ok, as long as The ideal rating is a guarantee of performance. I can't ask him to bring 5 dismonds in for a head to head, trying to use the ideal rating to do that up front
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,760
dumbo|1425315128|3840750 said:
MelisendeDiamonds|1425311767|3840722 said:
dumbo|1425279698|3840603 said:
Looking at several diamonds, I noticed that the AGS Ideal light rated diamonds are often scoring fairly poor on the HCA scale. Is the HCA just an estimate? One I looked at had a 2.8 score, another a 3.7. Does that mean the AGS Ideal light performance rating is weaker than the HCA elimination tool? Or that the HCA is just an estimate, a good way to weed out poor performers, but also a tool that lets strong performers get eliminated unnecessarily?

Of course, there are still plenty of AGS ideal diamonds that score under a 2, but being the AGS ideal rating is fairly strict, I would have guessed it was pretty much 100% scoring at or under 2. Please explain, it is a bit confusing!

The AGSL ray tracing system is far superior to HCA it takes into account all facets from an actual scan. HCA is a rejection tool and a flawed one at that due to the limited inputs of averaged and rounded measurements. The author or HCA prefers shallow combinations and penalizes deeper combinations putting more emphasis on spread considerations as such it has a bias which is not found in the more objective AGSL system.

Despite this the two systems should have good agreement in the middle of their ranges, on some borders they differ but those are marginal choices and difficult to select without inspecting the stones in hand on a case by case.

One guess to explain your observations is that If the ones you are considering are AGS 0000 but primarily score higher on HCA I'd say you are probably sacrificing cut to fit a particular budget and if thats the case I'd probably stick to GIA graded XXX stones instead and not pay the premium for the borderline AGS 0000 stones.


Thanks. Actually, the ones I was considering were all AGS 000 (to weed out under performers) but they all scored kinda low on HCA (you had said high). One had a 36.5 crown and pavilion, another a 34.8 crown and 41.1 pavilion, both were 62/55 otherwise. My understanding initially was that an AGS 000 diamond is a guaranteed good performer. You are right though, these are selling at perhaps a $1000 premium for 2ct, not the $4000 premium that a super ideal commands.

Unfortunately, the vendor, while very helpful and PS approved, does not have an idealscope. The AGS document also does not have a light map. Which could be ok, as long as The ideal rating is a guarantee of performance. I can't ask him to bring 5 dismonds in for a head to head, trying to use the ideal rating to do that up front
I'm not answering for Haroutioun, but I would say that it depends on the level of cut quality that you are striving for and the relative weight you are putting on other factors. The AGS Ideal standard is pretty strict so even outliers will be outstanding from a light performance perspective.
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
14,633
dumbo|1425315128|3840750 said:
Thanks. Actually, the ones I was considering were all AGS 000 (to weed out under performers) but they all scored kinda high (poorly) on HCA (you had said high, assuming you meant a high number, not a good score). One had a 36.5 crown and pavilion, another a 34.8 crown and 41.1 pavilion, both were 62/55 otherwise. My understanding initially was that an AGS 000 diamond is a guaranteed good performer. You are right though, these are selling at perhaps a $1000 premium for 2ct, not the $4000 premium that a super ideal commands.

Unfortunately, the vendor, while very helpful and PS approved, does not have an idealscope. The AGS document also does not have a light map. Which could be ok, as long as The ideal rating is a guarantee of performance. I can't ask him to bring 5 dismonds in for a head to head, trying to use the ideal rating to do that up front
The hca is a little too harsh on some diamonds with a pavilion just over 41.
Depending on the minor facets and specific angles in the average which ags takes into account they can be just fine.
What is the date on the report to make sure it is not the old looser style report?

There are AGS0 diamonds I would not consider and the hca can point them out and there are 2 different grading systems from AGS that had an ideal grade one pre 2005 one newer.
However the hca can alert on combos that are just fine and AGS new system passes them.
So what ends up being needed is to take everything into account.
IS/ASET images would answer many of the questions.

What was the pavilion angle on the one with a 36.5 crown?
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,760
Karl_K|1425323627|3840804 said:
dumbo|1425315128|3840750 said:
Thanks. Actually, the ones I was considering were all AGS 000 (to weed out under performers) but they all scored kinda high (poorly) on HCA (you had said high, assuming you meant a high number, not a good score). One had a 36.5 crown and pavilion, another a 34.8 crown and 41.1 pavilion, both were 62/55 otherwise. My understanding initially was that an AGS 000 diamond is a guaranteed good performer. You are right though, these are selling at perhaps a $1000 premium for 2ct, not the $4000 premium that a super ideal commands.

Unfortunately, the vendor, while very helpful and PS approved, does not have an idealscope. The AGS document also does not have a light map. Which could be ok, as long as The ideal rating is a guarantee of performance. I can't ask him to bring 5 dismonds in for a head to head, trying to use the ideal rating to do that up front
The hca is a little too harsh on some diamonds with a pavilion just over 41.
Depending on the minor facets and specific angles in the average which ags takes into account they can be just fine.
What is the date on the report to make sure it is not the old looser style report?

There are AGS0 diamonds I would not consider and the hca can point them out and there are 2 different grading systems from AGS that had an ideal grade one pre 2005 one newer.
However the hca can alert on combos that are just fine and AGS new system passes them.
So what ends up being needed is to take everything into account.
IS/ASET images would answer many of the questions.

What was the pavilion angle on the one with a 36.5 crown?
This is a good point Karl.

Look for the words Light Performance on the document to be sure the individual diamond has been graded by the ray tracing engine. Prior to 2005 grading was done by matching a collection of data points to look-up tables to estimate performance, much like GIA and HCA do. Even after rolling out the LP system AGS continued to offer proportion based reports.

A light performance based grade of Ideal is your best assurance of outstanding overall optics.
 

diamondseeker2006

Super_Ideal_Rock
Premium
Joined
Jan 11, 2006
Messages
58,547
We don't recommend using the HCA on AGS Ideal cut stones at all. The ideal cut grade plus an actual ASET or idealscope image is what is needed. We use the HCA to help us screen the better diamonds out of the wide GIA Excellent category. I would not take a chance on stones with those measurements without the extra images.
 

MelisendeDiamonds

Shiny_Rock
Trade
Joined
Jul 2, 2014
Messages
234
dumbo|1425315128|3840750 said:
Thanks. Actually, the ones I was considering were all AGS 000 (to weed out under performers) but they all scored kinda high (poorly) on HCA (you had said high, assuming you meant a high number, not a good score). One had a 36.5 crown and pavilion, another a 34.8 crown and 41.1 pavilion, both were 62/55 otherwise. My understanding initially was that an AGS 000 diamond is a guaranteed good performer. You are right though, these are selling at perhaps a $1000 premium for 2ct, not the $4000 premium that a super ideal commands.

Unfortunately, the vendor, while very helpful and PS approved, does not have an idealscope. The AGS document also does not have a light map. Which could be ok, as long as The ideal rating is a guarantee of performance. I can't ask him to bring 5 dismonds in for a head to head, trying to use the ideal rating to do that up front

I would start a new thread with specific examples and some of the experienced regulars can help you with this. As long as you post the grading report link directly from the lab I believe trade members are allowed to comment as long as a vendor is not mentioned.
I also think in a new thread the Prosumers can consider your budget and suggest alternative options and reasoning instead of talking in general terms.

I think it will be difficult for anyone to answer for you, the value proposition between a generic AGS 0000 verus a branded Super Ideal, some of that tradeoff would be "mind clean" issues and some of it may be actual discernible visual differences to those with a keen eye.

I know of two easy ways to solve this dilemma, just spend the extra money and go for the "mind clean" or "best possible", or try to do a comparison in person yourself and decide if the premium is justified. I think you will find opinions split on this issue especially on Pricescope with a high concentration of very cut minded individuals. Your opinion or that of the intended wearer is more important than ours. Either way you won't be ending up with a poorly cut diamond by any means if you stick with AGS 0000 makes.

In any case if you care this much to be asking such in depth questions I suspect actual photographed images are going to be an important part of your choice.

I would caution against purchasing diamonds with older grading reports, there are usually reasons(mostly negative) why diamonds with older reports have been sitting in the pipeline for such a long time.
 
Be a part of the community Get 3 HCA Results
Top