Question re GIA Rating Vs. HCA Score

[togal]

I am wondering if anyone can tell me how a diamond can have specs that put it squarely in the "Excellent" range on the GIA cut table, yet only score a 3.4 on the HCA? Just curious. (I''m sure there''s a very complicated answer to this, but hopefully one that my little pea-brain can understand

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[Fly Girl]

Take a look at the dotted box on the HCA colored graph. That is the GIA Excellent box, and the angles can be either terrific (red part of the graph), or terrible (blue part of the graph). When I was looking at diamonds, I used the HCA to be sure my stones had GIA Excellents that also landed in the red part of the HCA graph.

For more details, there are many, many threads describing the issues the experts here have with the GIA Excellent cut rating.

 

[Garry H (Cut Nut)]

Hi, I am David,

and here is the complicated response to a letter from Goliath

http://journal.pricescope.com/Articles/50/1/Letter-to-the-Editor-of-the-Australian-Gemmologist.aspx

 

[strmrdr]

Without the numbers then an IS image its impossible to say which is wrong.
In general I find the HCA properly applied better than the GIA cut grade but neither is infallable and should be only used as a low confidence first filter.