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HCA results - confused!?

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hawaiianorangetree

Ideal_Rock
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Jan 17, 2009
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2,692
Hi everyone

I was hoping someone could shed some light on the confusion i have created for myself.

i have a gia excellent cut round brilliant diamond. (we don''t see to many ags ones in oz).

Anyway, i was just putting the depth and table % and the crown and pavillion angles into the hca and it come back with a score of 3. Not as good as i was expecting for the sparkle that the diamond had when i saw it in the store.

Anyway, being bored i decided to put the depth and table % in as well as the % for the crown and pavillion that were listed on the certificate and it has now come back with a HCA score of 1.6.

Is this possible or what am i missing?

I''m sure there is a reasonalbe explanation for this, i just wanted to know what it was!!!
 

Lorelei

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
42,064
Date: 2/6/2009 5:13:37 AM
Author:hawaiianorangetree
Hi everyone

I was hoping someone could shed some light on the confusion i have created for myself.

i have a gia excellent cut round brilliant diamond. (we don't see to many ags ones in oz).

Anyway, i was just putting the depth and table % and the crown and pavillion angles into the hca and it come back with a score of 3. Not as good as i was expecting for the sparkle that the diamond had when i saw it in the store.

Anyway, being bored i decided to put the depth and table % in as well as the % for the crown and pavillion that were listed on the certificate and it has now come back with a HCA score of 1.6.

Is this possible or what am i missing?

I'm sure there is a reasonalbe explanation for this, i just wanted to know what it was!!!
Angles are more accurate than percentages for crown and pavilion, can you post the numbers you were entering please?
 

Stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
Messages
14,069
From what I understand, this is cause by rounding errors. HCA has also noted that it is more accurate when using the angles then % depth.

For GIA the crown and pavilion angles are from an average of 8 facets each and then rounded of to steps of 0.5degrees for the crown angles and 0.2degree for the pavilion angles.

Using these numbers and the table %, the crown height and pavilion depth is obtained, another rounding to the nearest 0.1%.

Then, if you input the crown and pavilion depth into the HCA, it converts it back to the angles, another rounding error is introduced. So 2 additional sets of rounding errors are introduced into the equations if crown and pavilion depth is used for the HCA. Depending on which way the rounding occurs during the 2 conversion stage, the score could be better or worse.

Hope that helps.
 

hawaiianorangetree

Ideal_Rock
Joined
Jan 17, 2009
Messages
2,692
ok thank you i thought it would be something like that!!

here are the specs...

1.05 carat 6.53 - 6.56 f colour si1

depth 61.4%

table 57%

crown angle 34

pavillion angle 41.2

crown height 14.5%

pavillion depth 43.4%

ok now don''t be too nasty.... my bf was given the instructions of excellent excellent excellent and he delivered... plus i really love it and he has put the deposit on it.
 

hawaiianorangetree

Ideal_Rock
Joined
Jan 17, 2009
Messages
2,692
cheers Gary if only i could afford one of yours!!! lol

Date: 2/6/2009 5:26:15 AM
Author: Garry H (Cut Nut)
angles are far more accurate.
It will not be a dog, but when dirty (95% of the time) it will loose it a bit
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
Date: 2/6/2009 5:37:52 AM
Author: hawaiianorangetree
ok thank you i thought it would be something like that!!


here are the specs...


1.05 carat 6.53 - 6.56 f colour si1


depth 61.4%


table 57%


crown angle 34


pavillion angle 41.2


crown height 14.5%


pavillion depth 43.4%


ok now don''t be too nasty.... my bf was given the instructions of excellent excellent excellent and he delivered... plus i really love it and he has put the deposit on it.
Depending on what is in the averages that combo can work.
What is the lower half %.
It will be 80%(preferred for that combo) 75% or not likely but possible 85%(good) or 70%(not so good) on the report.
 

hawaiianorangetree

Ideal_Rock
Joined
Jan 17, 2009
Messages
2,692
Date: 2/6/2009 6:10:38 AM
Author: strmrdr

Date: 2/6/2009 5:37:52 AM
Author: hawaiianorangetree
ok thank you i thought it would be something like that!!


here are the specs...


1.05 carat 6.53 - 6.56 f colour si1


depth 61.4%


table 57%


crown angle 34


pavillion angle 41.2


crown height 14.5%


pavillion depth 43.4%


ok now don''t be too nasty.... my bf was given the instructions of excellent excellent excellent and he delivered... plus i really love it and he has put the deposit on it.
Depending on what is in the averages that combo can work.
What is the lower half %.
It will be 80%(preferred for that combo) 75% or not likely but possible 85%(good) or 70%(not so good) on the report.
star length 55%

lower half 80%

medium faceted girdle

cut polish and finish excellent excellent excellent.
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
Date: 2/6/2009 6:21:30 AM
Author: hawaiianorangetree

star length 55%


lower half 80%


medium faceted girdle


cut polish and finish excellent excellent excellent.
that will help.
We would need an IS image to tell you more.
Within the gia rounding of those numbers there are some combos that can work very well.
 
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