HCA vs. Cut grading

[ppass]

If i understood the HCA charts correctly, the best stones are marked with red/orange color.
The ideal/excellent ranges of AGS and GIA are also marked.
But the red interval is usually much wider then GIAs Ex.

Are there really any stones on the market, that have HCA scores < 2 with excellent brillance
but also have a cut grading worse then ideal/excellent?

 

[Lorelei]

Date: 1/29/2009 8:03:33 AM
Author:ppass

If i understood the HCA charts correctly, the best stones are marked with red/orange color.
The ideal/excellent ranges of AGS and GIA are also marked.
But the red interval is usually much wider then GIAs Ex.

Are there really any stones on the market, that have HCA scores < 2 with excellent brillance
but also have a cut grading worse then ideal/excellent?

Welcome!

Ok first thing, ideal cut pertains only to AGS0 Ideal cut grade, any other use of the term does not guarantee you a well cut diamond. AGS are considered to be the strictest cut grader. GIA Excellent's criteria for this grade is wide and can encompass less desirably proportioned diamonds such as steep deeps which can score badly on the HCA despite having the Ex cut grade and these are usually not the best looking diamonds due to typical light leakage which these angle combos, but of course there can be occasional exceptions and grey areas. So yes you can have diamonds which score <2 on the HCA and can have GIA Very Good cut grade for example, they can be given this grade for various reasons, a couple we see here can be for a very thin girdle, girdle treatments etc but the diamond overall has proportions which score well on the HCA.

But if you are new to this, the HCA is used to eliminate diamonds, not select them. It cannot physically see the diamond and can only estimate how well a certain set of proportions is likely to work together. The procedure goes like this when selecting, if the HCA is used, then the aim is to collate the diamonds which score <2, which are considered a ' pass pending further evaluation.' Also aim for diamonds generally which hit both AGS and the GIA box, not essential but this is the bullseye. This evaluation is done with Idealscope images, ASET in some cases and trusted vendor/ appraiser advice. This is also why we recommend working with a vendor who has inventory diamonds with all the cut analysis like IS images available so you can make an informed choice.

If you have Idealscope images and other info available then the HCA's use is limited anyway, so do not use it as a selection tool, rather to see if any diamond is worth more of your time and effort in evaluating further.

 

[stone-cold11]

Yes.

Especially the shallower pavilion angles for the respective crown angles. You will notice that AGS ideal and GIA ex grade are all in the upper region of the red/orange color, that is also in the young people''s ring range mark in the HCA explanation page, http://diamonds.pricescope.com/ideal.asp. Maybe targeting the market but they also perform well in other category noted on the HCA page.

 

[blastdoor]

Date: 1/29/2009 8:03:33 AM
Author:ppass

Are there really any stones on the market, that have HCA scores < 2 with excellent brillance

but also have a cut grading worse then ideal/excellent?

Hi, I have a direct answer to your question... Yes... the diamond I just bought for the ring I''ll be using to propose to my gf is of GIA VG Cut and still scores 0.7 on the HCA... see the thread here

 

[Sharon101]

Date: 1/29/2009 8:09:25 AM
Author: Lorelei

Date: 1/29/2009 8:03:33 AM
Author:ppass

If i understood the HCA charts correctly, the best stones are marked with red/orange color.
The ideal/excellent ranges of AGS and GIA are also marked.
But the red interval is usually much wider then GIAs Ex.

Are there really any stones on the market, that have HCA scores < 2 with excellent brillance
but also have a cut grading worse then ideal/excellent?

Welcome!

Ok first thing, ideal cut pertains only to AGS0 Ideal cut grade, any other use of the term does not guarantee you a well cut diamond. AGS are considered to be the strictest cut grader. GIA Excellent''s criteria for this grade is wide and can encompass less desirably proportioned diamonds such as steep deeps which can score badly on the HCA despite having the Ex cut grade and these are usually not the best looking diamonds due to typical light leakage which these angle combos, but of course there can be occasional exceptions and grey areas. So yes you can have diamonds which score <2 on the HCA and can have GIA Very Good cut grade for example, they can be given this grade for various reasons, a couple we see here can be for a very thin girdle, girdle treatments etc but the diamond overall has proportions which score well on the HCA.

But if you are new to this, the HCA is used to eliminate diamonds, not select them. It cannot physically see the diamond and can only estimate how well a certain set of proportions is likely to work together. The procedure goes like this when selecting, if the HCA is used, then the aim is to collate the diamonds which score <2, which are considered a '' pass pending further evaluation.'' Also aim for diamonds generally which hit both AGS and the GIA box, not essential but this is the bullseye. This evaluation is done with Idealscope images, ASET in some cases and trusted vendor/ appraiser advice. This is also why we recommend working with a vendor who has inventory diamonds with all the cut analysis like IS images available so you can make an informed choice.

If you have Idealscope images and other info available then the HCA''s use is limited anyway, so do not use it as a selection tool, rather to see if any diamond is worth more of your time and effort in evaluating further.

This is so well written. I vote for this explaination to be made into a sticky. Even I understood it!!!!!

 

[Lorelei]

Date: 1/29/2009 9:33:25 AM
Author: Sharon101

Date: 1/29/2009 8:09:25 AM
Author: Lorelei

Date: 1/29/2009 8:03:33 AM
Author:ppass

If i understood the HCA charts correctly, the best stones are marked with red/orange color.
The ideal/excellent ranges of AGS and GIA are also marked.
But the red interval is usually much wider then GIAs Ex.

Are there really any stones on the market, that have HCA scores < 2 with excellent brillance
but also have a cut grading worse then ideal/excellent?

Welcome!

Ok first thing, ideal cut pertains only to AGS0 Ideal cut grade, any other use of the term does not guarantee you a well cut diamond. AGS are considered to be the strictest cut grader. GIA Excellent''s criteria for this grade is wide and can encompass less desirably proportioned diamonds such as steep deeps which can score badly on the HCA despite having the Ex cut grade and these are usually not the best looking diamonds due to typical light leakage which these angle combos, but of course there can be occasional exceptions and grey areas. So yes you can have diamonds which score <2 on the HCA and can have GIA Very Good cut grade for example, they can be given this grade for various reasons, a couple we see here can be for a very thin girdle, girdle treatments etc but the diamond overall has proportions which score well on the HCA.

But if you are new to this, the HCA is used to eliminate diamonds, not select them. It cannot physically see the diamond and can only estimate how well a certain set of proportions is likely to work together. The procedure goes like this when selecting, if the HCA is used, then the aim is to collate the diamonds which score <2, which are considered a '' pass pending further evaluation.'' Also aim for diamonds generally which hit both AGS and the GIA box, not essential but this is the bullseye. This evaluation is done with Idealscope images, ASET in some cases and trusted vendor/ appraiser advice. This is also why we recommend working with a vendor who has inventory diamonds with all the cut analysis like IS images available so you can make an informed choice.

If you have Idealscope images and other info available then the HCA''s use is limited anyway, so do not use it as a selection tool, rather to see if any diamond is worth more of your time and effort in evaluating further.

This is so well written. I vote for this explaination to be made into a sticky. Even I understood it!!!!!

* BIGGEST blush*, you are so kind, your sweet words are so much appreciated Sharon!!!

 

[ppass]

Ok, thanx for all!

 

[Lorelei]

Date: 1/31/2009 8:47:56 AM
Author: ppass
Ok, thanx for all!

You are most welcome, let us know if you need any more help!