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HCA question

breanne

Shiny_Rock
Joined
Jun 7, 2016
Messages
188
My HCA score is a 1.2, which I was happy with, but I never quite understood the chart. From my understanding now, the solid white border means the stone is AGS ideal, while the dotted represents GIAXXX. Here is a photo of my HCA X within that chart, it falls between both borders, what does this mean?

_5026.jpeg
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,175
That means your stone has both GIA X AND AGS ideal proportions AND HCA less than 2.0. A hat trick. This is how I select my stones.
 

breanne

Shiny_Rock
Joined
Jun 7, 2016
Messages
188
Would you look at that! Lol! I knew the proportions were great, but I see many people's different opinions on what ratios are best for rounds. What exactly is the ags/gia ideal range anyway? (ps, love your hat trick reference, very Canadian of you :) )
 

flyingpig

Ideal_Rock
Premium
Joined
Nov 7, 2015
Messages
2,175
There is no set GIA X/AGS 0 crown and pavilion ranges. They change depending on the table size. Punch in different numbers for table %. You will notice the shape of the dotted and solid line borders change or even disappear. To make it more complicated, star length and lower girdle length are also taken into consideration.

In general, GIA's cut grading system is more lenient. However, no diamond with pavilion angle of less than 40.5 qualifies for GIA X (which is apparent when you look at the dotted border), whereas AGS may allow such stones for AGS0.

If you really want to study.... then.
https://www.americangemsociety.org/Content/uploads/85441435072031.pdf
http://diamondcut.gia.edu/pdfs/booklet_cut_estimation_tables_lowres.pdf
This is one of the reasons why I only buy and recommend AGS/GIA stones. They make it very clear and explain how they cut systems are designed, to public.
You go to IGI or EGL website. You get no information.
 
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