HCA score 0.7? 1? 1.5?

[diamond86guy]

I understand the HCA score should not be used to choose diamonds but rather be used as a tool to eliminate bad diamonds against those which are good.

So i have come across many diamonds with varying scores below 2.

Sometimes with a score of 0.4, 1.0, 1.1 you will be expected to get an all round excellent return like this:

Light Return: Excellent
Fire: Excellent
Scintillation: Excellent
Spread: Excellent

However i have also seen results with a score of 0.7 or 1.1 with one factor being 'Very Good'?

Light Return: Excellent
Fire: Excellent
Scintillation: Excellent
Spread: Very Good

This is something i have not been able to understand. My question is, what do these numbers mean? I understand that if the score is lower than 2 its a good diamond to choose. But after it scores below 2 you get varying results and varying scores?

Clearly the lower the HCA score doesn't always necessarily mean it's a great diamond if a factor is displaying as 'Very Good' as opposed to an 'Excellent' all round result with a higher score of 1.0?

I hope i have explained myself well.

 

[bmfang]

The general rule is that a score under 2.0 means that a stone is worthy of consideration. Other factors then come into play like the inclusions, how does the stone actually look, etc. So you could find a stone which has a great HCA score but it looks like a dogs breakfast due to the inclusions it had inside it or it has fluorescence which causes the stone to look lifeless. It is not a tool for selection of a diamondto urchsse as it only takes into account a limited data set.

The spread is essentially a measure as to whether the stone has been cut too shallow in an attempt to retain carat weight. HCA does not require a stone to have a perfect/excellent spread in order for a score of 2.0 or less to be had.

 

[diamondseeker2006]

Almost every hearts and arrows top cut diamond will score Ex on the first three and very good on spread. That is because ideal cuts generally are cut for balance and not cut shallow for greater diameter.

These are measurements to help you stay in ideal cut territory with a GIA excellent cut stone.

table: 54-58

depth: 60-62.3

crown angle: 34-35.0 (up to 35.5 crown angle can sometimes work with a 40.6 pav angle)

pavilion angle: 40.6-40.9 (sometimes 41.0 if the crown angle is close to 34)

 

[WinkHPD]

Garry Holloway, the developer of the HCA likes the shallow stones as they spread bigger. He will be the first to tell you that there is no relative ranking based on 0.5, 1, 1.5 etc. At 2 and below, the diamond is worthy of more consideration. You should not use the scores as selection criteria.

Wink

 

[eugchen]

so is the lower the HCA the better?

i guess the HCA mainly tells you how well a diamond is "Cut", but obviously cannot rate the color, clarity, size...

so one must examine the rest of these parameters.

 

[Lore]

so is the lower the HCA the better?

No, I think that is exactly opposite to what Wink just said. There is no "better" or "worse" if the diamond scores 1.3 vs 1.5. Any diamond scoring under 2.0 should be worth another look but doesn't always mean that it's worth buying. Folks here recommend looking at the Idealscope and ASET images as the next step to check on light leakage.

 

[ringo865]

It is a rejection tool, use it to weed out those scoring OVER 2. Stones under 2 would be candidates for further evaluation using other selection tools, idealscope, ASET, opinions of pricescopers …

 

[Laura diamond]

Almost every hearts and arrows top cut diamond will score Ex on the first three and very good on spread. That is because ideal cuts generally are cut for balance and not cut shallow for greater diameter.

These are measurements to help you stay in ideal cut territory with a GIA excellent cut stone.

table: 54-58

depth: 60-62.3

crown angle: 34-35.0 (up to 35.5 crown angle can sometimes work with a 40.6 pav angle)

pavilion angle: 40.6-40.9 (sometimes 41.0 if the crown angle is close to 34)

Wow. I watched hundreds of videos and I spend a lots of time to get close to this numbers But you said it in the most clear way I've seen. Thank you a lot.

I am just looking for an upgrade for my wedding ring and I was looking for this exactly.

Thank you again I know this is an old comment but thanks anyway

 

[musicloveranthony]

I don't ascribe to the idea that it's even useful to weed out any stone above a 2 unless there are other reasons to weed it out (like asymmetry, unpleasant inclusions, visible graining, milky fluorescence, etc).

I look at the images and videos with my eyes first, then at the specialty scope images, then finally at the HCA if it does well on all the other criteria. I don't expect the HCA to tell me anything I don't already know - it's more of a confirmation.

 

[Jax172]

My engagement diamond scores two excellents and two very goods. But I bought it from GOG and they did all the tests on it and deemed it a beautiful diamond. So I’m not bothered that it doesn’t get 4 excellents on the HCA. It’s a helpful tool to decide if a diamond is worth looking into further but it’s not the final say on wether it is worthy of purchase.

 

[sledge]

My engagement diamond scores two excellents and two very goods. But I bought it from GOG and they did all the tests on it and deemed it a beautiful diamond. So I’m not bothered that it doesn’t get 4 excellents on the HCA. It’s a helpful tool to decide if a diamond is worth looking into further but it’s not the final say on wether it is worthy of purchase.

This is the correct approach. HCA is basically to get you in the ballpark. Additional research, etc is required to reach a final decision.

I don't ascribe to the idea that it's even useful to weed out any stone above a 2 unless there are other reasons to weed it out (like asymmetry, unpleasant inclusions, visible graining, milky fluorescence, etc).

I look at the images and videos with my eyes first, then at the specialty scope images, then finally at the HCA if it does well on all the other criteria. I don't expect the HCA to tell me anything I don't already know - it's more of a confirmation.

You are certainly welcome to shop for stones however you please, but in case a newbie is reading this, I think some additional explanation is required.

Before we dig in, I agree that if you DO have advanced images (ASET, IS, H&A, etc) those will always supersede the HCA.

That said, HCA is simply checking the proportions to see if the reported values have a reasonable shot of working in unison with one another.

For instance, here is a stone with a 57 table, 62.8 depth and 36c/41.4p combo.



I don't have to run an HCA to tell you not to buy this stone. That steep 36 crown paired with a steep 41.4 pavilion is not going to perform well. The stone was cut for weight retention and not maximum light return. An advanced image like ASET or IS would confirm this (if one were available).

Yet average Joe doesn't even know what those values mean, let alone how they work in harmony together. What he does see is a stone that meets his size, color & clarity requirements for a price he likes and that has a GIA 3x report.

After all, a trusted lab said it's "excellent". How bad could it really be? Using HCA may let him see this and help him avoid a $45k mistake (true price of stone being referenced).

 

[Eriel]

Hello, i have a question, im looking at three diamonds with an HCA score of 1, 1.2, 1.5

But based on their measurements, they either seem shallow or at bad angle, why would they be rated so high?

1.53 carat Diamond #1
HCA score: 1.5
Measurements: 7.32x7.39x4.54
Depth: 61.7
Table: 58
Crown: 35.6
Pavilion: 40.6

1.52 carat Diamond #2
HCA score: 1.0
Measurements: 7.34x7.39x4.48
Depth: 60.8
Table: 59.5
Crown: 35
Pavilion: 40.5

1.53 carat Diamond #3
HCA score: 1.2
Measurements: 7.51x7.53x4.45
Depth: 59.3
Table: 59.5
Crown: 33.3
Pavilion: 40.8

May someone please help to narrow down my choice?

 

[Wink]

Garry Holloway, the developer of the HCA likes the shallow stones as they spread bigger. He will be the first to tell you that there is no relative ranking based on 0.5, 1, 1.5 etc. At 2 and below, the diamond is worthy of more consideration. You should not use the scores as selection criteria.

You cannot use the HCA as a selection tool. These scores tell you the stones are worthy of further consideration. Many, if not most here, would not favor these diamonds and would keep looking...

Wink