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Help With Low Hca Score But Gia Triple Ex


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Hi everyone


I have just recently bought a round brilliant loose diamond to put on an engagement ring once I find the right design :). I was pretty happy with the stone as on paper it seemed like a good buy with a triple ex score on the GIA cert and a excellent cut based on the AGS proportion chart. However after running the specs into HCA program it has given the diamond a 4.2 score (Good). I would like to ask if anyone can shed some light into why this diamond may have a low HCA score and with the attributes listed below, what maybe some of the negative aspecs of this diamond?


From looking at other diamond specs i have noticed that the crown height is quite low and the pavillion angle is pretty steep. However i am not sure if these are negative aspecs of this diamond as a whole.


I have seen the diamond with my eyes however I have never been great at differentiating diamonds with my eyes and to be honest I could barely notice the differences on all the diamonds that have been shown to me. My partner however has much better eyes then i do and may notice much more. I wish i could bring her to see the diamond prior but then it wouldn't be surprise!


Measurements 7.28 - 7.34 x 4.37

Carat - 1.4

Colour - E

Clarity - IF

CUT - Excellent

Polish - Exellent

Symmetry - None

Flurescence - None


Table - 59%

Crown height - 12.5%

Pavillion Depth - 44.5%

Total Depth - 59.8%

Crown Angle - 31.5

Pavillion Angle - 41.8

Lower girdle / half facet length - 80%

Girdle Thickness - 3%

Star length - 45%

Cutlet - None



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The answer comes down to personal preferences: Garry Holloway does not like diamonds with relatively deep pavilions and steep pavilion angles because they are less bright than others. GIA's research done through about 300 people including consumers, dealers and gemmologists indicates that quite a few people like them (one can then argue that the reason at least some dealers and cutters like them is because they have a higher yield from rough,).


The really interesting question is: do you like it? Have you compared it to other diamonds? Do you still like it?


If the answer to these three questions is "yes", then feel free to ignore the HCA and GIA.


(FWIW - in this specific case, and based on the numbers, I would tend to agree with the HCA; I'd certainly sacrifice both colour and clarity to get a better cut).

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The biggest criticism of GIA-x is that it’s overly broad and indeed it covers something like half of the stones sent to the lab.  A hunt for mainstream sorts of stones, say a one caratish, eye clean, white, round, produces THOUSANDS of results with GIA-x cut grades.  How can you possibly choose?   Some can be done by arbitrary manipulation of the requirements.  1.01-1.02 carats, VS1, F.  There are still hundreds.  Would a 1.03 or a VS2 probably have been sufficient?  For most people yes, but you have to do something to bring down the list.  It’s silly but it works.  Most people who hit this wall are trying to pick a stone blind based purely on the data found on the GIA report.  They haven’t seen the stone, and the person selling it hasn’t even seen it. 

This is not the way in-person shopping is done.  There you tell the salesperson you want a clean white carater, they produce a few stones, you ask a bunch of questions, and pick one (or not).  The filter that narrowed the selection was the dealer.   Cynics would say that the criteria used is dealer margin or just what they happen to have and optimists would say it’s hiring an expert to help make a difficult choice.  The reality is usually somewhere in the middle and it depends on your jeweler.  That’s not a gemological property and it’s the reason that you will consistently find advice on the forum from every one of the pros that you should choose your dealer first and the diamond second rather than the reverse.  This is true for online shoppers too by the way.  Your chances of success go way way up if your jeweler is your ally rather than your opponent and the the DIY approach using the HCA as a replacement is full of trouble.  If you find or even suspect that your jeweler isn’t deserving of your trust, don’t just pass on the stone, pass on the jeweler.   When you do find a jeweler you find to be trustworthy, either online or in your neighborhood, use ‘em.  Then wrap an uninvolved professional appraiser into it at the end.  Trust but verify.

I’m not all that big on the GIA cut grade, but the REASON that they give for being so inclusive is that not everyone agrees on what is best.  That’s a good reason. When you ask people what they want, they always say brightness, fire and scintillation.  They want ‘sparkle’.  Good enough.  But when you actually start showing them stones and have them force rank them, you get dramatically different results.  This is even true when you do it in standardized environments with clean stones, good lighting, trained observers and without time pressure, all of which are arbitrary limitations.  So now what? The GIA solution to this problem was to collect hundreds of thousands of observations where people force rank several stones from a pool of several dozen, and notice which ones were consistently at the top and which were consistently at the bottom.  That is 100% a measure of popularity.   It works well for jewelers and merchants who are extremely interested in filling their cases with things that are popular, but it falls apart when an individual consumer tries to use it as a predictor of what they are going to like the best.  Dealers want to know what’s likely to SELL.  That's their definition of the best.   If your taste is a little outside the statistical average, does that make you wrong?  Obviously not.  And the GIA solution is to make very broad categories.  The ‘best’ are the top half (or more), and Very Good is ¾ of the remainder.  That may be reasonable in some grand artistic sense but it makes for a scale that’s almost completely useless as a selection criteria.  It’s a place to start, but it’s definitely not the end.

Edited by denverappraiser
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