Reserved a diamond, but a bit worried about the HCA...

[darknezx]

Hi all,

I am getting a proposal ring for my girlfriend. She's in the dark, but I know she's not the picky sort and will be over the moon with anything I present to her.

I've paid a deposit for this gem: http://www.gia.edu/cs/Satellite?reportno=5146657022&childpagename=GIA%2FPage%2FReportCheck&pagename=GIA%2FDispatcher&c=Page&cid=1355954554547


Diamond Dossier

0.64 carat
F
VS1
GIA, triple excellent

Proportions
Depth: 62.3 %
Table: 56 %
Crown Angle: 35.5°
Crown Height: 15.5%
Pavilion Angle: 41.0°
Pavilion Depth: 43.5%
Star Length: 50%
Lower Half: 80%
Girdle: Medium, Faceted, 3.5%
Culet: None

To the naked eye, everything seemed ok, and the prices quoted were pretty cheap compared to local prices here. When I checked the HCA scores, I realise that it scores below par, 3.8. Now, to my eye, it looks better than a HCA gem that I compared with that scored 2.2.

Should I be worried about the HCA score? Hard to understand why a triple excellent can get such a low HCA score?

Thanks in advance guys!

 

[Strawberries1]

Subscribed!

 

[Just_Starting]

HCA uses 4 of 57 facets to make a guess at how well the diamond will do (4 important facets). That's good for eliminating diamonds, most people on here would eliminate that stone based on that HCA. If you like it and the price is competitive then may still be worth it. I will say however that there are stones that perform much better out there.

What timescale are you working to? If time is on your hands it might be worth taking a better look around. Also where do you live? Easier access to quality vendors in some areas compared to others.

 

[JDDN]

GIA triple X encompasses a very large range so you will get varying degrees of performance within the GIA 3X category. Thus, not all GIA 3X stones will get a score under 2 on the HCA. The HCA is one tool you can use to weed out stones that will not perform as nicely as other stones. It does not guarantee a beautifully performing stone. It merely tells you that it has promise and you should investigate further.

The stone you plugged is a bit deep and the CA and PA are steep. Many like the look of these types of stones, but they may not perform as well as a stone with a shallower CA and PA. It also may look a little small for it's carat size.

Could you find better? Yes. Will you find better in your budget? Not sure. Will your GF notice if it's not performing top notch? Depends on her.

 

[John P]

HCA uses 4 of 57 facets to make a guess at how well the diamond will do (4 important facets).

Slight correction. The HCA uses five data points. The Table and Culet (if one's present) are facets. The Crown Angle/% and Pavilion Angle/% you enter are each an average of eight facet measurements. Depth% is not a facet but relates to spread... So a total of 17 facets (18 if a culet exists) are being assessed, although single numbers standing for multiple measurements makes things fuzzy.

What the HCA does not take into account is 40 minor facets (of 57 total on the diamond). It does not account for cut-consistency. It does not account for 3D optical precision. It does not account for indexing. None of that information is present. The HCA is imagining a "chalk outline" of averaged (sometimes rounded) Table, Crown and Pavilion data, and predicting whether the presumed angles are "safe" or not. That's its intended use, and it's useful in that context; to reject some diamonds and ID others worth further consideration. Garry Holloway is very clear on the fact that it should not be used for specific selection.

When using GIA reports the output becomes a bit more uncertain: Because of rounding, GIA 57T 34.5C 40.8P could actually be 57T 34.3 40.7 or 57T 34.7C 40.9P. That toggles between HCA 1.3 to 1.8. So a single diamond can vary on the HCA, simply based on how the lab reports the information.

In Context:

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

From an earlier thread:
[URL='https://www.pricescope.com/community/threads/hca-score-of-9-vs-1-9-which-is-a-better-score.199300/']https://www.pricescope.com/community/threads/hca-score-of-9-vs-1-9-which-is-a-better-score.199300/[/URL]

 

[diamondseeker2006]

John, may I please quote you from your last post (giving you credit, of course)? I have tried so many times to tell people it is dangerous to buy solely by numbers and I love your analogy!

 

[John P]

Absolutely DS. And honored that you'd like to quote it. Thanks!

 

[Just_Starting]

Thanks for the info John

 

[Rockinruby]

HCA uses 4 of 57 facets to make a guess at how well the diamond will do (4 important facets).

Slight correction. The HCA uses five data points. The Table and Culet (if one's present) are facets. The Crown Angle/% and Pavilion Angle/% you enter are each an average of eight facet measurements. Depth% is not a facet but relates to spread... So a total of 17 facets (18 if a culet exists) are being assessed, although single numbers standing for multiple measurements makes things fuzzy.

What the HCA does not take into account is 40 minor facets (of 57 total on the diamond). It does not account for cut-consistency. It does not account for 3D optical precision. It does not account for indexing. None of that information is present. The HCA is imagining a "chalk outline" of averaged (sometimes rounded) Table, Crown and Pavilion data, and predicting whether the presumed angles are "safe" or not. That's its intended use, and it's useful in that context; to reject some diamonds and ID others worth further consideration. Garry Holloway is very clear on the fact that it should not be used for specific selection.

When using GIA reports the output becomes a bit more uncertain: Because of rounding, GIA 57T 34.5C 40.8P could actually be 57T 34.3 40.7 or 57T 34.7C 40.9P. That toggles between HCA 1.3 to 1.8. So a single diamond can vary on the HCA, simply based on how the lab reports the information.

In Context:

Just imagine that you're trying to get to know someone's looks and personality...

An HCA score is merely like having a chalk outline of the person.
Grading report numbers are like having the person's height, weight and clothing measurements.
An ASET or Ideal-Scope (for RB) image is like having a still photo of the person.
An AGS Platinum "0" in performance is like a panel of judges confirming that the person's personality and looks are solid.
A 3D scan in sophisticated cut-calculation software is like having a video interview with the person.

Eventually, it's a lot of great information. All told it's enough for an experienced cut-specialist to make very detailed performance predictions. But in the end, a live date (dinner & a movie?) will be how you finally judge total personality and looks as you, individually, perceive them.

From an earlier thread:
[URL='https://www.pricescope.com/community/threads/hca-score-of-9-vs-1-9-which-is-a-better-score.199300/']https://www.pricescope.com/community/threads/hca-score-of-9-vs-1-9-which-is-a-better-score.199300/[/URL]

Great information! That is the best analogy!

 

[darknezx]

Hi guys, thanks for the advice! Am soaking it up and hopefully absorbing the collective wisdom of all the experts here

I went back to the drawing board, and asked for a different diamond, this time with more specificity than just "show me what you have". I have been offered this: http://www.gia.edu/cs/Satellite?pagename=GST%2FDispatcher&childpagename=GIA%2FPage%2FReportCheck&c=Page&cid=1355954554547&reportno=5196056822

Now, I haven't gone down to take a look, and may not have access to a ideal scope. From the original gem, I'm being quoted a 14% increase in price, although it does seem the results from the AGA tool and HCA tool are much better. Any ideas on whether to take a punt?

 

[Strawberries1]

According to the HCA tool this should be a good one worth enquiring further!

 

[diamondseeker2006]

Hi guys, thanks for the advice! Am soaking it up and hopefully absorbing the collective wisdom of all the experts here

I went back to the drawing board, and asked for a different diamond, this time with more specificity than just "show me what you have". I have been offered this: http://www.gia.edu/cs/Satellite?pagename=GST%2FDispatcher&childpagename=GIA%2FPage%2FReportCheck&c=Page&cid=1355954554547&reportno=5196056822

Now, I haven't gone down to take a look, and may not have access to a ideal scope. From the original gem, I'm being quoted a 14% increase in price, although it does seem the results from the AGA tool and HCA tool are much better. Any ideas on whether to take a punt?

No. This one has a 32.5 crown angle. Too low!

Let me give you some parameters within that should help a little. These are not absolute guarantees of a perfect stone, but it gets you into ideal cut territory for the most part. If you can't access idealscope, etc., then I surely would use these parameters. And I always personally buy stones within these parameters.

table: 54-58

depth: 60-62.3

crown angle: 34-35.0

pavilion angle: 40.6-41.0

 

[darknezx]

Hi guys, thanks for the advice! Am soaking it up and hopefully absorbing the collective wisdom of all the experts here

I went back to the drawing board, and asked for a different diamond, this time with more specificity than just "show me what you have". I have been offered this: http://www.gia.edu/cs/Satellite?pagename=GST%2FDispatcher&childpagename=GIA%2FPage%2FReportCheck&c=Page&cid=1355954554547&reportno=5196056822

Now, I haven't gone down to take a look, and may not have access to a ideal scope. From the original gem, I'm being quoted a 14% increase in price, although it does seem the results from the AGA tool and HCA tool are much better. Any ideas on whether to take a punt?

No. This one has a 32.5 crown angle. Too low!

Let me give you some parameters within that should help a little. These are not absolute guarantees of a perfect stone, but it gets you into ideal cut territory for the most part. If you can't access idealscope, etc., then I surely would use these parameters. And I always personally buy stones within these parameters.

table: 54-58

depth: 60-62.3

crown angle: 34-35.0

pavilion angle: 40.6-41.0

Thanks for the advice. I know that the crown angle is low, essentially I would be sacrificing fire for brilliance?

Also, am puzzled how this would score well on HCA and GIA?

 

[John P]

Thanks for the advice. I know that the crown angle is low, essentially I would be sacrificing fire for brilliance?

Roger that. If it's cut with good consistency and the actual measurements don't stray far from the reported/rounded averages, it will be very bright. You'll still have fire in the mix but the dispersive fans won't be as wide as diamonds with more room in the crown.

Also, am puzzled how this would score well on HCA and GIA?

The HCA is just saying "Chalk outline good. It's worth further consideration." And it is.

The placement in EX is interesting. Sure enough, GIA facetware results say EX. However, if the star length had been 50% it would have been GIA VG. That's a bizarre threshold, relatively speaking, since the stars have far less influence than most of the other facet groups. And since GIA rounds stars to the nearest 5% you could have two identical diamonds...one with 47% stars (rounded to 45%) and another with 48% stars (rounded to 50%)...which would be placed a cut-grade apart from each other.


I would say the 75% lower halves is worth checking out. This facet group can have notable influence, and GIA rounds that number to the nearest 5% too. While reported as 75%, if the average is actually 77% it will be to be to the benefit of overall performance paired with that crown. But if the average is actually 73% the wider pavilion mains may suffer from darkness/obstructions in some close viewing conditions. An ideal-scope or ASET image would allow an estimate of that feature, as well as a look at overall cut-consistency.

For the record: The numbers reported are predicted as an AGS 2 candidate.