HCA spread weighting

[kaigun02]

Hello folks,

I''m a first time buyer trying to understand as much as I can before I take the plunge. I''ve been searching the internet far and wide for the perfect diamond and running many through the Holloway Cut Advisor. I was wondering if its creator or someone else familiar with the math involved could comment on how the final number is developed. In particular, I''m curious how heavily spread is weighted into the overall grade. I''ve run a couple diamonds that came up excellent in all other factors but had "very good" spread. Since I can compare diameters easily on my own, I''m mostly interested in the light performance. Does anyone know how much the score of an otherwise excellent diamond is bumped up by a less than ideal spread? I''m guessing there''s no easy answer given the vagueness of a term like "very good," but still curious if anyone can shed a little light on the subject.

-J

 

[Lorelei]

Date: 7/26/2009 6:52:33 AM
Author:kaigun02
Hello folks,

I'm a first time buyer trying to understand as much as I can before I take the plunge. I've been searching the internet far and wide for the perfect diamond and running many through the Holloway Cut Advisor. I was wondering if its creator or someone else familiar with the math involved could comment on how the final number is developed. In particular, I'm curious how heavily spread is weighted into the overall grade. I've run a couple diamonds that came up excellent in all other factors but had 'very good' spread. Since I can compare diameters easily on my own, I'm mostly interested in the light performance. Does anyone know how much the score of an otherwise excellent diamond is bumped up by a less than ideal spread? I'm guessing there's no easy answer given the vagueness of a term like 'very good,' but still curious if anyone can shed a little light on the subject.

-J

All but the more shallow diamonds get VG for spread, this is normal and not something to worry about, 60.3% is the cutoff between ex and vg spread.

 

[Ellen]

Date: 7/26/2009 6:54:42 AM
Author: Lorelei

All but the more shallow diamonds get VG for spread, this is normal and not something to worry about, 60.3% is the cutoff between ex and vg spread.

Ditto!

 

[kaigun02]

Ellen and Lorelei,

Thanks for the responses. What I''m most interested to know, though, is if there''s any sort of correction I can apply to take spread out of the equation. So, if 60.3 is the cutoff for Excellent and I were looking at a stone with 62.0% depth, is there some percentage I could factor in to get a corrected HCA score? I''m essentially trying to mathematically eliminate spread from the calculations as much as possible.

Thanks!

-J

 

[Garry H (Cut Nut)]

spread is a weight function to diameter to weight - not a %
www.diamond-cut.com.au has a full explanation - there is a page just on spread.