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Question about a GIA certified triple x that scores 4.8 HCA

junhox212

Rough_Rock
Joined
May 15, 2012
Messages
73
i came across this GIA certified F SI1 triple ex .3 carat diamond on Zoara.com which is also listed as hearts and arrows on their site. When i put in the numbers on Holloway cut adviser it gave out a score of 4.8 and the following results. I am just wondering if anyone know how this diamond with these specs yield such horrible results on the HCA. (GIA Report 1225685009) Anyone?

Holloway Cut Adviser
Selected: 61.7% depth, 59% table, 35.5° crown angle, 41.2° pavilion angle,
The result is for a symmetrical diamond with a medium girdle and very good polish
HCA scores were adjusted Dec. 15, 2001 and Feb. 6, 2003.

Factor Grade
Light Return Good
Fire Fair
Scintillation Fair
Spread Very Good
Total Visual Performance 4.8 - Good - Only if price is your main criterion
 

kenny

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
28,132
Re: Question about a GIA certified triple x that scores 4.8

Reject rounds scoring over 2.0 on the HCA.
Keep shopping.
Since round is the most abundant diamond shape I'd be picky and only buy one that does well by all cut-grading tools.

GIA knows who pays them so they made their so-called cut grades very loosey goosey.
That way they get lots of grading business and sellers get to save weight and sell diamonds that buyers think have excellent cut, but may be a cut below.

I respect GIA's color and clarity grading but not their cut grading. :nono:

BTW be sure to get an Idealscope image on all the rounds that do score under 2.0.
https://www.pricescope.com/tools/ideal-scope

Compare the image to this chart.
http://ideal-scope.com/reference-chart-ideal-scope-images/

screen_shot_2016-06-29_at_12.png
 

tyty333

Super_Ideal_Rock
Premium
Joined
Dec 17, 2008
Messages
21,646
Re: Question about a GIA certified triple x that scores 4.8

Like Kenny said, the GIA Excellent range is just to wide. They give stones an excellent grade that we would not recommend.
The pavilion angle for this stone is throwing it off.

You can have an H&A stone with bad angles. Plus, who designated H&A. Some vendors have strict guidelines for H&A, some
not so much. GIA does not grade a stone H&A (someone correct me if I'm wrong). It will put it on the certificate if that's
what it says on the girdle.
 

MissGotRocks

Super_Ideal_Rock
Premium
Joined
Jun 23, 2005
Messages
12,177
Re: Question about a GIA certified triple x that scores 4.8

Yes, that stone is known as a steep/deep with the crown and pavilion angles both being steep rather than complimentary. The net result is a loss of light return.

Definitely keep looking and use this guidelines to help you in your search:

Table 54-58
Depth no more than 62.2
Crown 34-35
Pavilion 40.6-40.9

Use the HCA and run the numbers through the AGA Cut Class tool as well for some additional feedback. Most AGS0 stones will fair well but as others have said, the GIA grading is much broader. Some GIA triple x stones will just not fair as well.
 

junhox212

Rough_Rock
Joined
May 15, 2012
Messages
73
Re: Question about a GIA certified triple x that scores 4.8

Thank you for your responses. A hypothetical question, if a GIA certified diamond with a very good cut grade yields a HCA score below 2 but a triple ex with a score of 4.8, will the very good cut be the better choice?
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,171
Re: Question about a GIA certified triple x that scores 4.8

junhox212|1467329938|4050285 said:
Thank you for your responses. A hypothetical question, if a GIA certified diamond with a very good cut grade yields a HCA score below 2 but a triple ex with a score of 4.8, will the very good cut be the better choice?
No. HCA has limitations. Try 60/55/30/41.5. An obviously terrible combo of crown and pav. But it scores 1.6 excellent. It is unable to recognize a terrible combo of extreme angles. You want a stone that is HCA score of less 2.0 AND GIA Ex. Not one or the other.

It ia possible to find a "very good" cut diamond with decent numbers. But it is likely to have durability issue (very thin girdle) or not enought spread (very thick girdle and/or high depth) You dont want these issues either.
 

fair75

Rough_Rock
Joined
May 28, 2015
Messages
87
Re: Question about a GIA certified triple x that scores 4.8

Just like what other posters have said, you can use the HCA score to weed out bad performers. Therefore, it is a rejection tool only. If you have access to IS/ASET scope images, you wouldn't need HCA. If you don't know how to interpret the scope images, post them on here and someone will most likely be able to help you out.
 
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