Confused by a very good GIA cut scoring excellent on HCA

[dar7]

So I have an excellent cut GIA that scored very good on th HCA, a 3 to be exact and there is a very good cut GIA I have my eye on because the numbers look so good. Turns out it scored excellent a 0.3 on the HCA, how is this so?

 

[Texas Leaguer]

The GIA Excellent category is quite broad on one hand, and the HCA tool does not take into account everything impacting a GIA grade, for instance polish and symmetry. HCA is a rejection tool. Focus on diamonds scoring around 2 or less. Consider those scoring over two if other conditions are met, such as good ASET and IdealScope images or AGS Ideal report.

 

[Gypsy]

What are the numbers. You still have to watch depth and stuff with the HCA. Even if it scores well. HCA is rudimentary rejection tool. Not a selection tool. It uses four data points to predict how a diamond may perform. That's all.

 

[Karl_K]

hca scores well some diamonds with shallower pavilions that are better suited for pendants and earrings where GIA gives them a VG which is about right for in a ring but put them in a pendant or earring and they are great and the hca is right and gia wrong. The metrics are different is all.
I am pretty confident the one scoring .3 on the hca will fall into that category.

One the other hand some steep deep diamonds can score gia EX and the hca properly dings them with a score over 2.
One the other hand if you have 3... gia gives EX to some slightly steep/deep stones that the HCA is overly harsh and they are ok even with a score over 2 on hca.
In general for me it takes a real aset or IS image to override a score of 2+ on the hca.

 

[dar7]

Interesting.

 

[luvdajules]

Thanks, Karl...that's the longest post I've seen from you and such a detailed description

 

[MelisendeDiamonds]

So I have an excellent cut GIA that scored very good on th HCA, a 3 to be exact and there is a very good cut GIA I have my eye on because the numbers look so good. Turns out it scored excellent a 0.3 on the HCA, how is this so?

Haven't played with the HCA numbers in a while but from what I remember low scores <0.5 have shallow pavilion angles which can cause darkness/head shadow issues.
GIA might be right in the downgrade to VG if its for a ring. It really depends on lower half angles which neither system takes into account as an input.

 

[dar7]

Very helpful, thank you Karl!

 

[Karl_K]

Your welcome.