Cut Advice Please, GIA v IGI

[daph]

I've posted previously on this but would like some advice on cut grading...

From reading the GIA cut article (see link) and looking at the HCA cut grader, I see that some of the GIA examples of excellent cut stones will give lower scores for scintillation and fire than the stone I have (IGI excellent cut).

http://www.gia.edu/research-resources/cut-microsite-pdfs/estimating_cut_grade_chart_lowres.pdf

For example,
HCA gives the following:
Present stone: Light return:Good Fire: Excellent Scintillation: Excellent (Overall score: 3.4 with fisheye warning)
GIA Example of excellent cut: Light return: Very good Fire: Very Good Scintillation: Good (Overall score: 2.8

How do people interpret this? If the jeweler comes back with a GIA excellent cut stone (such as one on the GIA article) - is it possible that overall, it won't look as well as the stone I have already, i.e., just good/very good across the board as opposed to the excellents for some aspects of present stone? Or could it be that it will be just marginally better on paper but perhaps with less scintillation and that the present stone will look better overall?

 

[Christina...]

GIA has a larger percentage of stone that will receive their excellent cut grade as opposed to AGS for example. Many feel that GIA cut criteria is too broad, so there are definitely stones within this category that will have a more appealing visual appearance than others, of course this depends on what YOU find appealing.

In general we suggest finding a stone what score below 2 on the HCA but definitely below 3, and then obtaining more information on the stone, such as ideal scope, magnified images, a gemological assessment etc. And keep in mind that the HCA is a rejection tool used to weed through massive online inventories, it's not a selection tool. It basis it's analysis on four proportions only, it will, on occasion allow a beautifully performing stone to fail and an underachiever to pass, this is why additional information is important. We have seen stones graded for ideal light performance by AGS score very poorly on the HCA so it's not the be all end all in diamond selection, though I think it's a very important tool for narrowing down you search and it does it's job quite well.


ETA the easy answer is yes, it's possible that your IGI EX stone has a better cut than the GIA stone, the problem with IGI is that they are often times softer on color and clarity grading than GIA which is the most accurate and consistent lab in the world...along with AGS. I'm not familiar with IGIs cut criteria so I can't comment on that specifically but I'm sure someone here can.