HCA Tool Grade and Symmetry question

[jootyhuynh]

Hello,

I recently used the pricescope HCA tool to get the total visual performance of my diamond. It came back with a 1.8. But it states: "The result is for a symmetrical diamond with a medium girdle and very good polish." If my diamond Symmetry on the GIA Certificate says it's "Very Good" does anyone know if 1.8 would be the true score? Or does the diamond have to be "Excellent symmetry" for the tool to work correctly?

 

[flyingpig]

Unfortunately, GIA (in fact, any grade report) report does not indicate the exact reason(s) for a grade deduction in polish/symmetry. Read this if you are interested.
https://diamondcut.gia.edu/pdf/polish_and_symmetry.pdf
There are plenty of stones with "very good" symmetry with amazing light return and appearance.
Also, there are plenty of stones with "excellent" symmetry with poor light performance and distorted appearance. It is possible to cut a diamond with enough deviations in angles and facet size that affect light return, but still good enough to obtain "excellent" symmetry.

Tough question to answer. In general, it is safer to get a stone with "excellent" symmetry. But "very good" can be just fine, in many cases. That's why you need the IS/ASET image.

 

[flyingpig]

https://www.pricescope.com/journal/what-aset-reveals-ideal-scope-does-not

IS/ASET is a selection tool, while HCA/AGA Guide is a screening tool.
If a stone has any significant symmetry/contrast/light return/leakage issue, the IS/ASET image will reveal.

I see you are interested in a 2.5c+ stone. I would not buy a stone without the IS/ASET in this price/carat range.

 

[ecf8503]

Symmetry refers to meet-point symmetry of the facets, not the optical symmetry of the stone itself.

 

[Texas Leaguer]

Hello,

I recently used the pricescope HCA tool to get the total visual performance of my diamond. It came back with a 1.8. But it states: "The result is for a symmetrical diamond with a medium girdle and very good polish." If my diamond Symmetry on the GIA Certificate says it's "Very Good" does anyone know if 1.8 would be the true score? Or does the diamond have to be "Excellent symmetry" for the tool to work correctly?

It's quite common for users to read too much into the results of the HCA tool. Even though it renders performance descriptions about light return, fire and scintillation, it cannot give you a 'total visual performance' of the diamond. There are many assumptions built into the tool, and a couple of those are stated in terms of good symmetry and polish. In actual fact, the tool only gets average and rounded inputs of a few key proportion factors. It does not take into consideration the "minor facets" including upper and lower girdle facets which together make a significant contribution to the actual performance of the diamond. Because of these and other limitations, the HCA tool is designed as a filter to eliminate stones with likely problematic basic geometry. Not as a selection tool or a performance evaluator.

That is where other diagnostic tools such as IS, ASET, H&A imagery come in.

 

[jootyhuynh]

It's quite common for users to read too much into the results of the HCA tool. Even though it renders performance descriptions about light return, fire and scintillation, it cannot give you a 'total visual performance' of the diamond. There are many assumptions built into the tool, and a couple of those are stated in terms of good symmetry and polish. In actual fact, the tool only gets average and rounded inputs of a few key proportion factors. It does not take into consideration the "minor facets" including upper and lower girdle facets which together make a significant contribution to the actual performance of the diamond. Because of these and other limitations, the HCA tool is designed as a filter to eliminate stones with likely problematic basic geometry. Not as a selection tool or a performance evaluator.

That is where other diagnostic tools such as IS, ASET, H&A imagery come in.

Can you tell if this is a good diamond https://www.jamesallen.com/loose-di...-color-vvs1-clarity-excellent-cut-sku-2613724

 

[Texas Leaguer]

As a member of the trade I am not allowed to recommend or criticize another vendor's diamond. But there are plenty of knowledgeable members here that can help you with that.
Good luck!