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HCA cut rating on GOG diamonds disappointing

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silverbuggy

Shiny_Rock
Joined
Feb 18, 2009
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188
I recently found the following HCA cut rating calculator:
https://www.pricescope.com/cutadviser.asp

It grades a diamond based on the following 4 factors:
Light Return
Fire
Scintillation
Spread

A score of 0-2 is in the Excellent range with 0 being almost impossible to achieve. A LOWER score is better.

I was testing it out on GOG hearts&arrows diamonds but was disappointed by the results.

http://goodoldgold.com/diamond/4755/
1.76ct E VS1 $31,477
Score = 1.5

http://goodoldgold.com/diamond/4871/
1.52ct D VS2 $28,884
Score = 1.5 with pavilion angle 41.0, but drops to 2.3 if 41.1. Actual is 41.05 degrees.

http://goodoldgold.com/diamond/4843/
1.91ct E VS2 $27,755
Score = 2.5

http://goodoldgold.com/diamond/5065/
1.79ct D VS2 $27,345
Score = 1.8 with pavilion angle 41.0, but drops to 2.5 if 41.1. Actual is 41.05 degrees.

-----------------------------------------------------------------------------------
2 questions for you experts and gemologists out there...

1) Shouldn''t a genuine hearts&arrows diamond have better ratings than this? I also tested a bunch of BlueNile signature-ideal diamonds with results much better than GOG''s diamonds...

2) Why does a 0.1 degree difference in pavillion angle cause such a big sway in the score?
 

Lorelei

Super_Ideal_Rock
Premium
Joined
Apr 30, 2005
Messages
42,064
Date: 2/22/2009 5:51:37 AM
Author:silverbuggy
I recently found the following HCA cut rating calculator:
https://www.pricescope.com/cutadviser.asp

It grades a diamond based on the following 4 factors:
Light Return
Fire
Scintillation
Spread

A score of 0-2 is in the Excellent range with 0 being almost impossible to achieve. A LOWER score is better.

I was testing it out on GOG hearts&arrows diamonds but was disappointed by the results.

http://goodoldgold.com/diamond/4755/
1.76ct E VS1 $31,477
Score = 1.5

http://goodoldgold.com/diamond/4871/
1.52ct D VS2 $28,884
Score = 1.5 with pavilion angle 41.0, but drops to 2.3 if 41.1. Actual is 41.05 degrees.

http://goodoldgold.com/diamond/4843/
1.91ct E VS2 $27,755
Score = 2.5

http://goodoldgold.com/diamond/5065/
1.79ct D VS2 $27,345
Score = 1.8 with pavilion angle 41.0, but drops to 2.5 if 41.1. Actual is 41.05 degrees.

-----------------------------------------------------------------------------------
2 questions for you experts and gemologists out there...

1) Shouldn't a genuine hearts&arrows diamond have better ratings than this? I also tested a bunch of BlueNile signature-ideal diamonds with results much better than GOG's diamonds...

2) Why does a 0.1 degree difference in pavillion angle cause such a big sway in the score?
A lower score is not better, where did you read this please? Not true.

The HCA is used to eliminate lesser performers as one of the first steps of evaluation. The aim is to score less than 2 in most cases, then such diamonds are considered a " pass pending further evaluation", this is done with ASET and Idealscope images, plus trusted vendor or appraiser advice.

Also concerning diamonds with a steeper pavilion angle, the HCA will lower the score for these so you need ASET or Idealscope to evaluate such diamonds.
 

arjunajane

Ideal_Rock
Joined
Jan 18, 2008
Messages
9,758
Huh? Three ratings under 2? Where''s the disappointment. Who told you that a lower score is better??
Once you have as many reflector images and analysis and detailed reports that GOG provide on their diamonds, HCA is null and void.
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
yep.. a lower score is not better.
Diamonds out to around 2.5 and some cases over can be of superb performance.
Anything 2 to 2.5 requires an aset or IS image for rejection.

Jon prefers and sells some combos that skirt the 2.0 zone on hca that are of top make.
When you get into that zone the minors and the range has to be good and gog selects diamonds that are excellent in both.
These combos are also some of my favorites.

I have seen in person some of these type that score just over 2 and I would buy them in a heartbeat.

Bottom line really is that aset/is > hca and the HCA has to be properly applied.
 

Ellen

Super_Ideal_Rock
Joined
Jan 13, 2006
Messages
24,427
Ditto Lorelei, aj and strm. Those are some gorgeous stones you picked.
 

silverbuggy

Shiny_Rock
Joined
Feb 18, 2009
Messages
188
Thanks for everyone''s feedback! I guess the HCA score isn''t comprehensive and in some cases not a good source of info.
 

John P

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,563
Date: 2/22/2009 5:40:41 PM
Author: silverbuggy
Thanks for everyone''s feedback! I guess the HCA score isn''t comprehensive and in some cases not a good source of info.
It''s a good resource but it''s only meant as a pass/fail indicator. For combos at the border more info is needed.
 

jet2ks

Ideal_Rock
Joined
Feb 3, 2009
Messages
2,022
Date: 2/22/2009 5:40:41 PM
Author: silverbuggy
Thanks for everyone's feedback! I guess the HCA score isn't comprehensive and in some cases not a good source of info.
The HCA is a tool, and like any tool can be misused. Diamond cutting is still part art and part science, so there is no way to predict with 100% accuracy what a stone will look like just by numbers. It is a great way, however, to quickly eliminate stones--any diamond that scores under 2 or maybe 2.5 has a greatly increased likelihood of performing well visually, thus cutting down the number of stones you have to physically look at (using an Idealscope or ASET) to find the one that works for you. You can find good visual performers with scores higher than 2, but you are going to have to look through a lot more stones in order to do so.

Comparing it to a totally different area, if you are wanting to buy a reliable car, your odds are really good that if you buy a Honda, everything will work great, but yet, even as good a reputation as Honda has as a car builder, an occasional lemon shows up. Conversely, if you buy a brand with a lesser reputation, you have a greater chance of ending up in the shop.
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
The hca plays it safe within the data it considers it would be rare to find a poor performing diamond that scores under 2 but you might find one more suited to a pendant or ear rings.
Because they do exist the HCA can only be used as a rough rejection filter.

Because it plays it safe it has been found to in some cases play it to safe.
There isn''t an easy answer because some combos can go both ways depending on factors the hca cant take into account.
The bottom line is that ASET/IS can overrule the hca score.
 
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