**HCA >2.0, but still performs?**

[msop04]

Has anyone owned or seen a diamond that scored >2 on the HCA, but looked great IRL? If so, what is the highest HCA score you've seen that this was true in your opinion? I know we tend to be nit-picky here on PS, but I'm interested to hear others opinions regarding this topic?

 

[msop04]

Anybody??

 

[Rockdiamond]

Hi Msop,
I don't want to open a can of worms...but yes.
About 3 and a half years back I purchased a diamond for my DW- since sold- that scored over 5 on HCA- it was a GIA "triple EX"
It was pretty sizable......she loved it. I loved it.....
She encouraged me to sell it....probably so she can torture me with that fact for the rest of my life

 

[Aerix]

I have! I own a diamond that's a GIA triple ex and only scores 3.5 on the HCA, but I can't really tell much of a difference when I compare it to a couple of AGS0 diamonds I have. All of them are under the 1 carat mark, so I'm not sure if that makes a difference either... But it still appears well cut to my eyes, despite the HCA score.

 

[msop04]

Hi Msop,
I don't want to open a can of worms...but yes.
About 3 and a half years back I purchased a diamond for my DW- since sold- that scored over 5 on HCA- it was a GIA "triple EX"
It was pretty sizable......she loved it. I loved it.....
She encouraged me to sell it....probably so she can torture me with that fact for the rest of my life

Wow!! Over 5 and still beautiful! Guess that just shows us that we judge with our eyes first! Thanks, RD!

 

[msop04]

I have! I own a diamond that's a GIA triple ex and only scores 3.5 on the HCA, but I can't really tell much of a difference when I compare it to a couple of AGS0 diamonds I have. All of them are under the 1 carat mark, so I'm not sure if that makes a difference either... But it still appears well cut to my eyes, despite the HCA score.

I know what you mean... mine (GIA XXX, 2.43ct) scored 2.6, and I'll be honest... I was kinda bummed out about it at first -- but, thankfully, I really can't tell a difference in it and several that scored <2. I had to quit thinking about it after a while since I do love it so! Thanks for sharing!

 

[msop04]

I know this is totally based on what we think is beautiful, but I love to hear stories like this! It's encouraging that a diamond without an ideal HCA can still be lovely!

...and I'm thankful I must not have "eagle eyes" when it comes to this! HA!

 

[diamondseeker2006]

My last rb had a score between 2 and 3 but I honestly never put the numbers through the HCA. I had an idealscope image and magnified pics so I could see that it was a great stone. I'd never recommend buying any diamond blind, but if someone absolutely has to, then I'd say go with less than 2 on the HCA to be safe. But certainly with an idealscope image and magnified photos of a stone, you can find winners in the range just above 2.

 

[Christina...]

I agree with DS. It's not unusual to find an AGS0 that scores below 2 on the HCA. Used for it's intended purpose HCA is a great tool, however it will and has missed some great stones, and it's passed some not so great ones. Buying blind is a risk and HCA helps to reduce that risk....it doesn't however eliminate it.

 

[Rhino]

Hi msop,

I have seen *many* that scored over 2.0 that were just fine, particularly when the HCA was geared to kill diamonds that hit the 41.0 pavilion angle mark. I've fielded so many questions on the technology I was forced to write an in depth article on the subject that I could refer people to so I wouldn't have to type it out each time.

This however was from a cutting facility that consistently produced precision cut diamonds utilizing a 34.x crown angle (sometimes 35.0) and were always superior Optical Symmetry Hearts & Arrow diamonds.

Garry and I are among a handful of gemologists who truly grasp and appreciate reflector based technologies and the HCA rightfully does ding diamonds with the 41.0 pavilion angle as it is a threshold angle that generally = blatant light leakage in round brilliant cuts under the table and on the lower half facets. I generally have referred to this in the past as the "ring of death" in previous posts.

The thing is this ... diamonds with 41.0 pavilion angles can be just fine however the *saving grace* that I have seen was superior or near superior Optical Symmetry (ie. H&A patterning) in precision cut diamonds. The fact that it was dinging perfectly fine diamonds (even under the FireScope which was the primary tool used to develop the HCA) disturbed me. Garry has since made adjustments and last I checked seemed pretty good although I don't use it today to make my buying decisions.

To consumer's I'd counsel this ... if a diamond does score over a 2.0 on the HCA but the seller *swears* it is just fine ... ASK FOR PROOF. If the diamond does indeed have a genuinely solid FireScope/IdealScope/DiamXray result there's your proof. Otherwise ... proceed with caution.

Kind regards,
Rhino

 

[msop04]

Hi msop,

I have seen *many* that scored over 2.0 that were just fine, particularly when the HCA was geared to kill diamonds that hit the 41.0 pavilion angle mark. I've fielded so many questions on the technology I was forced to write an in depth article on the subject that I could refer people to so I wouldn't have to type it out each time.

This however was from a cutting facility that consistently produced precision cut diamonds utilizing a 34.x crown angle (sometimes 35.0) and were always superior Optical Symmetry Hearts & Arrow diamonds.

Garry and I are among a handful of gemologists who truly grasp and appreciate reflector based technologies and the HCA rightfully does ding diamonds with the 41.0 pavilion angle as it is a threshold angle that generally = blatant light leakage in round brilliant cuts under the table and on the lower half facets. I generally have referred to this in the past as the "ring of death" in previous posts.

The thing is this ... diamonds with 41.0 pavilion angles can be just fine however the *saving grace* that I have seen was superior or near superior Optical Symmetry (ie. H&A patterning) in precision cut diamonds. The fact that it was dinging perfectly fine diamonds (even under the FireScope which was the primary tool used to develop the HCA) disturbed me. Garry has since made adjustments and last I checked seemed pretty good although I don't use it today to make my buying decisions.

To consumer's I'd counsel this ... if a diamond does score over a 2.0 on the HCA but the seller *swears* it is just fine ... ASK FOR PROOF. If the diamond does indeed have a genuinely solid FireScope/IdealScope/DiamXray result there's your proof. Otherwise ... proceed with caution.

Kind regards,
Rhino

Thank you so much for posting! I have learned a lot from all the experts that have weighed in on this topic, and I hope to hear from many more! I am not very familiar with the FireScope or DiamXray, but I look forward to learning more about them.

If anyone could post some links to threads concerning these two screening tools, I'd love to start my reading assignments.

 

[Rhino]

Hi msop,

Have you seen my article on the HCA?

 

[WinkHPD]

I agree with DS. It's not unusual to find an AGS0 that scores below 2 on the HCA. Used for it's intended purpose HCA is a great tool, however it will and has missed some great stones, and it's passed some not so great ones. Buying blind is a risk and HCA helps to reduce that risk....it doesn't however eliminate it.

Keep it up with those great answers and we will have to get a "Trade" button on you.

Rhino and I have the advantage of having other tools to use as well as the HCA, such as the Idealscope, the ASET etc which show us what to expect from the diamonds and we make our selections for our inventories by using those tools. In fact, for me, the HCA is the very last thing that I check, and never, NEVER have I used it to eliminate a stone that I have already chosen. Once or twice it has surprised me since Garry Holloway who devised it likes shallow cuts so some of the incredible stones that I like will score above a 2 if they are near the deeper end of my range.

(These comments do not apply to the Infinity diamonds, I do not remember ever seeing one above a 2, although it is possible.)

Wink

 

[Karl_K]

Sure there are diamonds over 2 hca that are nice performers.
When you get over 2 the lower half % and resulting angles become even more critical.
There is a sharp drop off at pavilion angles of 41.4+ even with nice looking IS/ASET images because of color retention.
The hca only looks at pavilion main averages(badly rounded ones if from GIA report) it does not consider the lowers in assigning the grade.

More info on lower halves being critical here:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

 

[Karl_K]

All of the above said I have seen a whole lot of diamonds with hca greater than 2 that were impacted by the angles and deficient in some ways compered to a modern tolk h&a.

 

[msop04]

Hi msop,

Have you seen my article on the HCA?

I'm quite certain I have seen it, but I need to go back and really read it. Thanks for reminding me about it!!

 

[msop04]

Sure there are diamonds over 2 hca that are nice performers.
When you get over 2 the lower half % and resulting angles become even more critical.
There is a sharp drop off at pavilion angles of 41.4+ even with nice looking IS/ASET images because of color retention.
The hca only looks at pavilion main averages(badly rounded ones if from GIA report) it does not consider the lowers in assigning the grade.

More info on lower halves being critical here:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

Thanks for weighing in, Karl_K!! I will definitely read this!

 

[Christina...]

I agree with DS. It's not unusual to find an AGS0 that scores below 2 on the HCA. Used for it's intended purpose HCA is a great tool, however it will and has missed some great stones, and it's passed some not so great ones. Buying blind is a risk and HCA helps to reduce that risk....it doesn't however eliminate it.

Keep it up with those great answers and we will have to get a "Trade" button on you.

Rhino and I have the advantage of having other tools to use as well as the HCA, such as the Idealscope, the ASET etc which show us what to expect from the diamonds and we make our selections for our inventories by using those tools. In fact, for me, the HCA is the very last thing that I check, and never, NEVER have I used it to eliminate a stone that I have already chosen. Once or twice it has surprised me since Garry Holloway who devised it likes shallow cuts so some of the incredible stones that I like will score above a 2 if they are near the deeper end of my range.

(These comments do not apply to the Infinity diamonds, I do not remember ever seeing one above a 2, although it is possible.)

Wink

Thanks Wink, that's a might big compliment!


msop I hope that you aren't beginning to doubt how beautiful your diamond is based on it's HCA score. Not too long ago I was looking for a specific type of light performance and was having trouble locating exactly what I was looking for...I decided to expand my search and with A LOT of guidance from veteran and trades people here, I decided to go outside of my comfort zone and purchase a stone that I might not have otherwise considered. Each and every time I look it, I'm glad I did. My particular stone had an excellent HCA and corresponding idealscope, it however feel outside of GIA EX, but remained an AGS1 (downgraded for polish) candidate. We hear everyday which stones to consider, and which not to around here, but in the end it really does all come down to what appeals to you. I ended up with a beautiful stone, and I'm sure you did too. Please don't doubt it's beauty based on 1 single measurement alone!

 

[Garry H (Cut Nut)]

I agree with DS. It's not unusual to find an AGS0 that scores below 2 on the HCA. Used for it's intended purpose HCA is a great tool, however it will and has missed some great stones, and it's passed some not so great ones. Buying blind is a risk and HCA helps to reduce that risk....it doesn't however eliminate it.

Keep it up with those great answers and we will have to get a "Trade" button on you.

Rhino and I have the advantage of having other tools to use as well as the HCA, such as the Idealscope, the ASET etc which show us what to expect from the diamonds and we make our selections for our inventories by using those tools. In fact, for me, the HCA is the very last thing that I check, and never, NEVER have I used it to eliminate a stone that I have already chosen. Once or twice it has surprised me since Garry Holloway who devised it likes shallow cuts so some of the incredible stones that I like will score above a 2 if they are near the deeper end of my range.

(These comments do not apply to the Infinity diamonds, I do not remember ever seeing one above a 2, although it is possible.)

Wink

Hi Wink,
The slight shallow diamond preference in HCA comes about largely because HCA gives bonus points / penalizes good / small spread.
It is the only system that gives a leg up for bigger spreads, and at the same time dings for likelhood of chipping from thin girdles and low crown angles.

HCA2 should be ready shortly, and it accounts for stereoscopic sight, so there will be many slightly deeper steeper stones that will score better. I have written about this and mentioned it over the years.
I have also added a symmetry bonus / penalty including +++ for H&A's and Ideal sym.

 

[teobdl]

Garry-is there an ETA of the HCA2? We're all licking our chops

 

[WinkHPD]

I agree with DS. It's not unusual to find an AGS0 that scores below 2 on the HCA. Used for it's intended purpose HCA is a great tool, however it will and has missed some great stones, and it's passed some not so great ones. Buying blind is a risk and HCA helps to reduce that risk....it doesn't however eliminate it.

Keep it up with those great answers and we will have to get a "Trade" button on you.

Rhino and I have the advantage of having other tools to use as well as the HCA, such as the Idealscope, the ASET etc which show us what to expect from the diamonds and we make our selections for our inventories by using those tools. In fact, for me, the HCA is the very last thing that I check, and never, NEVER have I used it to eliminate a stone that I have already chosen. Once or twice it has surprised me since Garry Holloway who devised it likes shallow cuts so some of the incredible stones that I like will score above a 2 if they are near the deeper end of my range.

(These comments do not apply to the Infinity diamonds, I do not remember ever seeing one above a 2, although it is possible.)

Wink

Hi Wink,
The slight shallow diamond preference in HCA comes about largely because HCA gives bonus points / penalizes good / small spread.
It is the only system that gives a leg up for bigger spreads, and at the same time dings for likelhood of chipping from thin girdles and low crown angles.

HCA2 should be ready shortly, and it accounts for stereoscopic sight, so there will be many slightly deeper steeper stones that will score better. I have written about this and mentioned it over the years.
I have also added a symmetry bonus / penalty including +++ for H&A's and Ideal sym.

Yes, you have, and I am pleased to see that you continue to improve your very useful product. I will continue to use it as part of my personal evaluation process and look forward to the new improved version. I will also continue to use my eyes as both the first and final test, since there is no combination of tools out there that can tell me better than my eyes tell me about what I like.

Wink

 

[Paul-Antwerp]

A small question, Garry:

If you are introducing a bonus/penalty for symmetry in the new version of HCA, you will need far more data than the average grading-report can offer you. How are you approaching that?

Live long,

 

[autumngems]

I hate to buy sight unseen but with my HCA of 0.6 I took a chance and am glad I did.

 

[Snicklefritz]

Yup! My previous diamond scored a 2.5 or so and was quite a dazzler! I'd buy one like it again in a heartbeat.

 

[Garry H (Cut Nut)]

A small question, Garry:

If you are introducing a bonus/penalty for symmetry in the new version of HCA, you will need far more data than the average grading-report can offer you. How are you approaching that?

Live long,

Of course Paul, in a perfect world we would not have 1/2 a degree crown angle rounding or the even worse 0.2 degree pavilion angle rounding either.
but as a rejection system with a lot of available diamonds HCA is one tool that serves many people. There are others who choose super ideal cuts like your stones, and HCA is not useful in that case because you and others like you provide Ideal-scope and ASET images, which make higher level rejection possible.

I have a total data set, but there was a problem with the break down data and that will be fixed when the maths wizz assisting me is back in town on monday.
Then we need to test the HCA app on Android, before starting on the Apple version.

it is taking 3x longer than I thought - having allowed for 1.5x

 

[Paul-Antwerp]

True, Garry, the rounding of averages on GIA-reports is another problem.

I am just wondering, if you are going to add a bonus/penalty for symmetry, where are you going to get the data necessary to enter?

Live long,

 

[Garry H (Cut Nut)]

True, Garry, the rounding of averages on GIA-reports is another problem.

I am just wondering, if you are going to add a bonus/penalty for symmetry, where are you going to get the data necessary to enter?

Live long,

I am not getting the info from anywhere Paul. users are inputting their own data.
I bet most will get it from a grading report.
I think you can remember the diamond I bought once that had fair H&A's patterns, but had GIA Good symmetry?
It might not be perfect, but I can not change that.

 

[msop04]

msop I hope that you aren't beginning to doubt how beautiful your diamond is based on it's HCA score. Not too long ago I was looking for a specific type of light performance and was having trouble locating exactly what I was looking for...I decided to expand my search and with A LOT of guidance from veteran and trades people here, I decided to go outside of my comfort zone and purchase a stone that I might not have otherwise considered. Each and every time I look it, I'm glad I did. My particular stone had an excellent HCA and corresponding idealscope, it however feel outside of GIA EX, but remained an AGS1 (downgraded for polish) candidate. We hear everyday which stones to consider, and which not to around here, but in the end it really does all come down to what appeals to you. I ended up with a beautiful stone, and I'm sure you did too. Please don't doubt it's beauty based on 1 single measurement alone!

Sorry, Christina -- I just saw this!!

To be honest, I did start to doubt it a little... but it was beautiful to me before I knew anything about HCA, and I still love it even after calculating the score. If I ever make a big diamond purchase again, it will probably be online, so all the measurements will help tremendously if it can't be viewed. I guess I was lucky to have been able to see my stone prior to purchase, because I almost certainly would have discarded it!

 

[Rhino]

Sure there are diamonds over 2 hca that are nice performers.
When you get over 2 the lower half % and resulting angles become even more critical.
There is a sharp drop off at pavilion angles of 41.4+ even with nice looking IS/ASET images because of color retention.
The hca only looks at pavilion main averages(badly rounded ones if from GIA report) it does not consider the lowers in assigning the grade.

More info on lower halves being critical here:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

ABSOLUTELY! Knowledge of lower half angles and length is *crucial* as well as knowing the variances. The reason Karl says this is because the lower half angles are cut steeper than the pavilion mains by default. The steeper the main angles the steeper the lower halves and they will be the first facets on the pavilion to suffer leakage. As Garry pointed out in another recent thread and posted an ASET of a GIA Ex gives a perfect demonstration of this.

Rhino

 

[karsa]

Sure there are diamonds over 2 hca that are nice performers.
When you get over 2 the lower half % and resulting angles become even more critical.
There is a sharp drop off at pavilion angles of 41.4+ even with nice looking IS/ASET images because of color retention.
The hca only looks at pavilion main averages(badly rounded ones if from GIA report) it does not consider the lowers in assigning the grade.

More info on lower halves being critical here:
https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant

ABSOLUTELY! Knowledge of lower half angles and length is *crucial* as well as knowing the variances. The reason Karl says this is because the lower half angles are cut steeper than the pavilion mains by default. The steeper the main angles the steeper the lower halves and they will be the first facets on the pavilion to suffer leakage. As Garry pointed out in another recent thread and posted an ASET of a GIA Ex gives a perfect demonstration of this.

Rhino

For a diamond with a tad bit shallower crown angle of 33, how will it affect the extent of fire/dispersion? I have been told that the brillance and fire of the external and internal reflections will inrease in intensity but as a trade off, there will be less dispersion/fire scintillations than a diamond with a higher crown angle like 34.5. What is your opinion on that?