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Can anyone explain the HCA calculator tool to a newbie?

morgin

Rough_Rock
Joined
Jan 17, 2013
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79
I thought I'd branch this off into a new thread because it was getting lost in my diamond search thread.

I understand from reading the HCA page and a couple other posts that the HCA calculator is a tool to use to weed out stones that are likely to underperform compared the the absolute best stones when you don't have the ability to examine them in person.

I also understand that it is based on some trig math to calculate expected performance based on the various angles, albeit there are limitations to knowing symmetry (which would be whether it looks H&A) polish and minor facets (the last one I don't think I understand fully, but my guess is that how the little facets on the diamond look that ultimately affect how it sparkles in person).

So, here's the question: I've come across some stones while searching the online vendors that have met the top level criteria imposed by GOG, WF, BG, etc, but which score 2 or higher (and in some cases, 3 or higher) on the HCA calculator.

if a stone scores a 3.8 HCA, but is still marketed by the reputable vendors as being a premium ideal cut stone with superior optical symmetry for H&A, is that because the HCA score is not indicitave of the performance, or that stones that score a 3.8 can still perform well, but it depends on the stone?

Is a stone that score 0-2 going to be inherantly more valuable and perform better than a stone scoring 2-4, or is it possible that a stone scoring a 1.5 could sit next to a stone scoring a 3.5, and all else being equal, the 3.5 is still the more beautiful stone?

When shopping online and relying upon vendors to assist in picking out their top cut stones in a given weight, how much deferrence should be given to HCA scores compared to the vendor's own assessment of the stone?
 
Also, here is an example of a stone I am currently looking at on GOG and discussing with them that scores a 3.8 (GIA graded)

http://www.goodoldgold.com/diamond/10450/

Light Return - Good
Fire - Very Good
Scintillation - Good
Spread - Very Good

However, GOG, who obviously is a very respected vendor and has been doing business with PSers for a long time and lots of people seem to love, thinks this stone is a top end stone and rejects the HCA score as being inconsistant with the actual performance based on the diamxray, aset, and general appearance in person.

In contrast, here is a AGS graded WF ACA stone that scores a 1.8 but is an I instead of an H:

http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2782664.htm

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

Prices are largely comparable between the two stones, and each respective vendor has rated them as the top cut class of stones they sell. However, the HCA scores are quite different, and one is a full colour score lower but around the same price.

If pushed to buy one of these, which would you buy? Would it just depend on price given both seem to be amazing? Vendor preference? Trusting the HCA calculator? Going with the better colour?
 
morgin|1363889325|3410430 said:
I thought I'd branch this off into a new thread because it was getting lost in my diamond search thread.

I understand from reading the HCA page and a couple other posts that the HCA calculator is a tool to use to weed out stones that are likely to underperform compared the the absolute best stones when you don't have the ability to examine them in person.

I also understand that it is based on some trig math to calculate expected performance based on the various angles, albeit there are limitations to knowing symmetry (which would be whether it looks H&A) polish and minor facets (the last one I don't think I understand fully, but my guess is that how the little facets on the diamond look that ultimately affect how it sparkles in person).

So, here's the question: I've come across some stones while searching the online vendors that have met the top level criteria imposed by GOG, WF, BG, etc, but which score 2 or higher (and in some cases, 3 or higher) on the HCA calculator.

if a stone scores a 3.8 HCA, but is still marketed by the reputable vendors as being a premium ideal cut stone with superior optical symmetry for H&A, is that because the HCA score is not indicitave of the performance, or that stones that score a 3.8 can still perform well, but it depends on the stone?

Is a stone that score 0-2 going to be inherantly more valuable and perform better than a stone scoring 2-4, or is it possible that a stone scoring a 1.5 could sit next to a stone scoring a 3.5, and all else being equal, the 3.5 is still the more beautiful stone?When shopping online and relying upon vendors to assist in picking out their top cut stones in a given weight, how much deferrence should be given to HCA scores compared to the vendor's own assessment of the stone?


I have seen this discussed before and can answer some of your questions. Future diamond purchasers on Pricescope are told to shoot for an HCA score under 2. But an HCA score of .7 is not necessarily better than one that is 1.5. Also, the HCA score is just a means to try and weed out inferior scores. But a diamond that gets a score over 2 is not necessarily a dud by any means. People here will tell you that ultimately your eyes are the best judgment.

As far as the first diamond you posted, I believe it got a high HCA rating because the Crown / Pavilion angles do not ideally complement each other. Does not mean it cannot be a beautiful diamond, however.
 
morgin|1363889325|3410430 said:
Is a stone that score 0-2 going to be inherantly more valuable and perform better than a stone scoring 2-4, or is it possible that a stone scoring a 1.5 could sit next to a stone scoring a 3.5, and all else being equal, the 3.5 is still the more beautiful stone?

Absolutely possible.

HCA can be difficult for newcomers because it's such an easy tool to use, and it's free, and it's easily accessed... it's very, very easy to misuse it. It's designed for one purpose only: to help you weed through a giant inventory by telling you if a stone is likely worth further investigation.

It's NOT telling you that a stone that scores < 2 is a winner. It COULD be a doozy. You need to investigate further.
It's NOT telling you that a stone that scores > 2 is a doozy. It COULD be a winner. You need to investigate further.
It's NOT telling you that a stone that scores > 2 ISN'T worth investigation. It's acknowledging that if you've got a hundred stones and no other info on any of them, you're going to have to make that list manageable somehow, even if it means knowingly eliminating some beauties.

With vendors like GOG and WF that provide a ton of info - scans, pics, in-person reviews of stones - you don't need HCA at all, you can just jump straight into that "investgating further" bit.
 
Ruby59 and Yssie, thank you so much for the very informative replies. That certainly puts my mind at ease (I also was provided with some materials from Marie at GOG who is quite lovely and she also made similar comments that HCA is not so useful in the final stages once it's already made it through initial cull.)

Anyone have any strong opinions if you had to choose between these two stones, provided prices were nearly identical? GOG stone is an H and WF is an I. Beyond that, I have no real strong feelings either way. It sounds like both are excellent vendors, both have great return and upgrade programs.

You pick, I buy!
 
morgin|1363901554|3410572 said:
Ruby59 and Yssie, thank you so much for the very informative replies. That certainly puts my mind at ease (I also was provided with some materials from Marie at GOG who is quite lovely and she also made similar comments that HCA is not so useful in the final stages once it's already made it through initial cull.)

Anyone have any strong opinions if you had to choose between these two stones, provided prices were nearly identical? GOG stone is an H and WF is an I. Beyond that, I have no real strong feelings either way. It sounds like both are excellent vendors, both have great return and upgrade programs.

You pick, I buy!

Does either vendor have the setting you want? Best to keep it all in one family if you can ::)
 
No - my setting is sufficiently custom and particular that I'd like to either have it done by someone like ERD/VC or locally by someone I can kind of interact with in person and see colours in person (I'm pretty particular about the colour of rose gold I want, which is hard to judge online). Leaning towards trying to still use a local designer whose work I do quite like, but we'll see what kind of thoughts ERD has (and I know I've seen that they are quite happy to work with GoG or WF stones in the past). VC hasn't replied back in a few days after a initial flury of e-mails, so I'm not sure if my setting style really interests him. We'll see!
 
morgin|1363891556|3410449 said:
http://www.goodoldgold.com/diamond/10450/

http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2782664.htm

If pushed to buy one of these, which would you buy? Would it just depend on price given both seem to be amazing? Vendor preference? Trusting the HCA calculator? Going with the better colour?

If *I* were pushed to one of these two - I'd go with the GOG - for me, the GIA H color wins out over AGL I - and I think the proportions of the GOG stone will result in a super bright diamond.

There is also a needle or something in the WF I stone - and even though it is VS2 and marked as eyeclean, I can see it in every single image - I know the images are super-enlarged and I may not see it in real life, but for me it is another reason why I'd choose the GOG stone in this case.

Since you are having a third party make the setting, you'll likely be receiving the diamond loose, right? So you'll have a chance to personally examine it - worst case, if it doesn't meet your expectations, return it - both vendors have excellent return policies - but honestly I do believe you'll be happy with either stone as long as you are comfortable with H/I color and as long as both are eyeclean to your preference.
 
People vary! I'd choose the WF. A slight increase in tint wouldn't bother me and I prefer the higher crown/shallower pav combo - I love seeing coloured light, and odds are better through a variety of lighting types.

Re. custom work - I've done several projects with different vendors and it can be very rewarding! Just make sure you and your chosen vendor are on the same page wrt. expectations for communication throughout the project, what happens if you don't like the result, etc. *before* you dive in ::)
 
Just to put my mind at ease- my GIA 3x ex BN sig ideal RB scores "just" 2.6 on the HCA. It's a fantastic, sparkly stone and the idealscope looks great to me, showing no light leakage. So does it mean DBF made the right choice and bought me a winner (don't get me wrong, I love the stone, so it's a winner anyway :mrgreen: ) ?
 
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