Interpreting the HCA

[paperumbrella]

I have identified a RB stone, which is listed as AGS 0. However, when I put the numbers into the HCA, it scores 3.5 and does not fall within the white outline, which is supposed to represent AGS 0 candidates. Here are the numbers:

Shape: Round Brilliant
Carat Weight: 1.59
Color: I
Clarity: Si1
Cut Grade: Ideal
Table %: 55.10
Depth %: 62.60
Girdle: Thin to Medium
Culet: N
Polish: Ideal
Symmetry: Ideal
Fluorescence: None
Measurements: 7.45-7.48x4.67
Length/Width ratio: 1.00
Crown angle: 35.6
Pavillion angle: 40.9
AGS #: 10404610410

Any ideas why this AGS 0-graded stone does not fall within the AGS 0 parameters on HCA?

 

[JulieN]

The AGS charts are guidelines, it is still possible to get a 0 outside of them sometimes.

 

[stone-cold11]

Please list the exact carat weight as stated on the report.

 

[Rockdiamond]

The HCA represents a scientific manner of picking stones suited to the taste of it's designer.
AGS and GIA both use different parameters for determining the quality of cut, meaning that a stone which may be extremely well cut might score low on the HCA.
By all means use your eyes.......

 

[ChunkyCushionLover]

I have identified a RB stone, which is listed as AGS 0. However, when I put the numbers into the HCA, it scores 3.5 and does not fall within the white outline, which is supposed to represent AGS 0 candidates. Here are the numbers:

Shape: Round Brilliant
Carat Weight: 1.59
Color: I
Clarity: Si1
Cut Grade: Ideal
Table %: 55.10
Depth %: 62.60
Girdle: Thin to Medium
Culet: N
Polish: Ideal
Symmetry: Ideal
Fluorescence: None
Measurements: 7.45-7.48x4.67
Length/Width ratio: 1.00
Crown angle: 35.6
Pavillion angle: 40.9
AGS #: 10404610410

Any ideas why this AGS 0-graded stone does not fall within the AGS 0 parameters on HCA?

That stone is on one of the edges of the AGSL 0 performance based grading range.
It would receive only a very good under the old AGS Gold Proportion based system which is what HCA tables correlate to.

However without looking up the grading report (we need the proper carat weight reported to 3 digits after the decimal) we couldn't tell you more.

One thing though it faces up a little smaller than a Tolk Ideal due to its overall depth and height of crown. But I wouldn't be dissuaded from purchasing it if the price is right.

A stone with these proportions will give up a little overall brightness but has the potential for more fire.

 

[paperumbrella]

Thank you so much for all of the replies thus far. I really appreciate the fast and insightful help. The exact carat weight from the AGS report is 1.598.

 

[stone-cold11]

Maybe the report number is wrong, I cannot retrieve the report.

Give it a try here. http://agslab.com/verify_diamond_grading_report.php

 

[paperumbrella]

Yep, I missed a 0 somewhere in my first post. The actual AGS number is 104046104010.
Here are the specs copied from the AGSL website:

AGS#: 104046104010
Report Type: The Platinum Light Performance Diamond Quality® Document
Shape and Style: Round Brilliant
Measurements: 7.45 - 7.48 x 4.67 mm
Cut Grade: AGS Ideal 0
Color Grade: AGS 2.5 (I)
Clarity Grade: AGS 5 (SI1)
Carat Weight 1.598
Fluorescence: Negligible
Comments:Additional clouds and surface graining are not shown.
Light Performance: 0
Polish: Ideal
Symmetry: Ideal
Table: 55.1%
Crown Angle: 35.6
Crown Height: 16.0%
Girdle: Faceted, 1.9% to 3.9%
Pavilion Angle: 40.9
Pavilion Depth: 43.1%
Star Length: 51%
Lower Girdle Length: 80%
Total Depth: 62.6%
Culet: Pointed

 

[yssie]

THe HCA uses four input parametres to do a quick and dirty blunt weeding. It does not consider all proportions of the diamond, and it is not failsafe - it is not intended to be failsafe. Beautiful diamonds are certainly possible outside the range that the HCA deems 'worthy'.

AGS for plat. report uses both proportions and a simulation of ray tracing to determine a cut grade (GIA and AGS gold use proportions only). Beautiful diamonds are certainly possible outside the range of AGS0, and stones that are marked down for pol/sym are exceptional values IMO.

YOUR eyes are the best judge of what you like and dislike. If I was on the hunt for a stone I'd snatch this one up for a look in-person, the higher crown and longer lgfs are my favourite make

 

[stone-cold11]

yap, looks good.

What Julien said.