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Beautiful Round Diamond sparkled, but only a 4.9 on HCA?

mnachmia31

Rough_Rock
Joined
Sep 8, 2011
Messages
14
Here are the GIA specifications for the diamond I am currently interested in:

Shape: Round Brilliant
Measurements: 7.67 - 7.75 x 4.82 mm
Carat Weight: 1.76 carat
Color Grade: H
Clarity Grade: VS1
Cut Grade: Excellent
Polish: Very Good
Symmetry: Very Good
Fluorescence: None

Total Depth: 62.5%
Table Size: 58%
Crown Angle: 35 degrees
Pavilion Angle: 41.2 degrees

Price: $19,000

The diamond looked amazing in person, sparkled wonderfully and is reasonably priced (well at least in my opinion please let me know what you think). I came home excited and just checked to see what its HCA score is and come to find out it only ranks at a 4.6 (Good and only worth buying if price is my main factor). Is this diamond not as great as I thought it was? Confused please help :???:
 

yssie

Super_Ideal_Rock
Premium
Joined
Aug 14, 2009
Messages
21,118
mnachmia31|1317156779|3027189 said:
Here are the GIA specifications for the diamond I am currently interested in:

Shape: Round Brilliant
Measurements: 7.67 - 7.75 x 4.82 mm
Carat Weight: 1.76 carat
Color Grade: H
Clarity Grade: VS1
Cut Grade: Excellent
Polish: Very Good
Symmetry: Very Good
Fluorescence: None

Total Depth: 62.5%
Table Size: 58%
Crown Angle: 35 degrees
Pavilion Angle: 41.2 degrees

Price: $19,000

The diamond looked amazing in person, sparkled wonderfully and is reasonably priced (well at least in my opinion please let me know what you think). I came home excited and just checked to see what its HCA score is and come to find out it only ranks at a 4.6 (Good and only worth buying if price is my main factor). Is this diamond not as great as I thought it was? Confused please help :???:
GIA rounds averages around eight sections of diamond, then rounds - crown to nearest 0.5%, pav up to nearest 0.1%. So from the GIA report, without any additional info, pics, professional opinion, we don't know anything about the range of measurements that went into that average, or how much the average was rounded by. We don't know about optical symmetry, only physical (facet-meet) symmetry. All of which, as you might imagine, make a *tremendous* difference in how a stone looks. In general, if you saw it in-person and if you compared it with other stones of similar size w/ different proportions in-person (in a variety of lighting types - this is important), your best bet is to trust your eyes to tell you what they like best.
 

kindred

Brilliant_Rock
Premium
Joined
Dec 3, 2008
Messages
945
Can you get an idealscope image from the vendor? If not, I would suggest buying your own and seeing how the diamond looks under it. It if looks good, that trumps the HCA score.
 

Regular Guy

Ideal_Rock
Joined
Jul 6, 2004
Messages
5,954
kindred|1317159535|3027252 said:
Can you get an idealscope image from the vendor? If not, I would suggest buying your own and seeing how the diamond looks under it. It if looks good, that trumps the HCA score.
I'm sympathetic to this.

Mayma, yes, AGS000 trumps HCA, for it's defining measures, especially if it is current, based on light performance.

But, Nachmia, I'd be cautious. Compared to what may be comparables here:

https://www.pricescope.com/diamond-search-results/209683

yours seems only averagely priced.

As we contemplated in another thread, it could be helpful to specifically compare to diamonds that are vetted by you and others as considered ideal and/or well cut. One diamond alone...it's hard to not look good.


Ira Z.
 

slg47

Ideal_Rock
Joined
Apr 4, 2010
Messages
9,667
another option is to compare it to an AGS0 stone or a GIA Ex that scores well on HCA and see what your eyes like best. make sure to compare in different lighting.
 

MissGotRocks

Super_Ideal_Rock
Premium
Joined
Jun 23, 2005
Messages
12,673
The HCA really dings a stone for a pavillion angle over 41. With a pavillion angle that high, it probably calls for a crown angle much lower and I'm sure the overall depth pulls it down as well.

IS would tell you a lot as do your own eyes. The HCA is a rejection tool not a selection tool and you've already selected the stone based on what you saw - that counts for something as well!
 

mnachmia31

Rough_Rock
Joined
Sep 8, 2011
Messages
14
I think my best bet right now is to purchase a beginner ideal scope kit to see for my own eyes. I also noticed that people are saying that I should check in different lighting conditions. From my initial view of the diamond, I noticed that it really sparkled when in direct light, but not so much when not in direct light. Is that to be expected?
 

slg47

Ideal_Rock
Joined
Apr 4, 2010
Messages
9,667
mnachmia31|1317170504|3027438 said:
I think my best bet right now is to purchase a beginner ideal scope kit to see for my own eyes. I also noticed that people are saying that I should check in different lighting conditions. From my initial view of the diamond, I noticed that it really sparkled when in direct light, but not so much when not in direct light. Is that to be expected?
yes but you should compare to a known good performer to see if there is a difference.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
15,747
mnachmia31|1317170504|3027438 said:
I think my best bet right now is to purchase a beginner ideal scope kit to see for my own eyes. I also noticed that people are saying that I should check in different lighting conditions. From my initial view of the diamond, I noticed that it really sparkled when in direct light, but not so much when not in direct light. Is that to be expected?
Yes
Take the advice and compare it to a stone with closer to tolkowsky proportions and make your own appraisal.
Also if this stone was dirty and was compared as above then you will find a dead dull zone just inside the table and dead outer facets making the stone look like one of 1.4ct
 

mnachmia31

Rough_Rock
Joined
Sep 8, 2011
Messages
14
Someone mentioned to compare this diamond to an AGS 0 diamond to see the difference. Don't these proportions fall into AGS 0?

AGS 0 criteria
Crown angle: 33.7 to 35.8
Pavilion angle: 40.15 to 41.20
Pavilion depth: 42.2 to 43.8
 

slg47

Ideal_Rock
Joined
Apr 4, 2010
Messages
9,667
mnachmia31|1317187421|3027627 said:
Someone mentioned to compare this diamond to an AGS 0 diamond to see the difference. Don't these proportions fall into AGS 0?

AGS 0 criteria
Crown angle: 33.7 to 35.8
Pavilion angle: 40.15 to 41.20
Pavilion depth: 42.2 to 43.8
under AGS proportion chart, 58 table/41.2 pav/35 crown gets 'excellent' not 'ideal'.

not all combinations of those angles will be AGS0.
 

slg47

Ideal_Rock
Joined
Apr 4, 2010
Messages
9,667
I downloaded it from AGS. I know they do grading by ray-tracing...not sure when the proportion chart is used.

I just posted part of it here...

58 41.2 28.5 Good
58 41.2 29 Very Good
58 41.2 29.5 Very Good
58 41.2 30 Excellent
58 41.2 30.5 Excellent
58 41.2 31 Excellent
58 41.2 31.5 Excellent
58 41.2 32 Ideal
58 41.2 32.5 Ideal
58 41.2 33 Ideal
58 41.2 33.5 Ideal
58 41.2 34 Ideal
58 41.2 34.5 Excellent
58 41.2 35 Excellent
58 41.2 35.5 Very Good
58 41.2 36 Very Good
58 41.2 36.5 Good
58 41.2 37 Good
58 41.2 37.5 Fair
 

Regular Guy

Ideal_Rock
Joined
Jul 6, 2004
Messages
5,954
slg47|1317188938|3027638 said:
I downloaded it from AGS. I know they do grading by ray-tracing...not sure when the proportion chart is used.
]
Maybe for their gold vs platinum?


Ira Z.
 

yssie

Super_Ideal_Rock
Premium
Joined
Aug 14, 2009
Messages
21,118
Do they even issue the old gold anymore?

I thought it had to be both - the stone had to have the right proportions by the charts and look nice in the simulation
 

Stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
Messages
14,069
Nope, it does not have to be.

That is just the cutter's guideline, when many stones failed to achieve AGS0 grade when the performance based grading was first introduced.
 

yssie

Super_Ideal_Rock
Premium
Joined
Aug 14, 2009
Messages
21,118
Stone-cold11|1317221634|3027793 said:
Nope, it does not have to be.

That is just the cutter's guideline, when many stones failed to achieve AGS0 grade when the performance based grading was first introduced.
Ah - thanks SC :bigsmile:
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
15,747
Yssie|1317220464|3027775 said:
Do they even issue the old gold anymore?

I thought it had to be both - the stone had to have the right proportions by the charts and look nice in the simulation
I believe they do, they probably should not as it appears to have hurt their brand.
Here are good reference charts that the cut Group and OctoNus have put together
http://www.octonus.ru/oct/mss/gia&agspgs.phtml

If the stone in question had say 41.1 pav and 34.8 crown and or with very tight symmetry is might well make AGS 0 on light performance.
But the chances in populations are greater that is would be 41.29, 35.2 and not as good because there are more steepish deepish GIA Ex than shallower stones.
 

yssie

Super_Ideal_Rock
Premium
Joined
Aug 14, 2009
Messages
21,118
Garry H (Cut Nut)|1317261349|3028394 said:
Yssie|1317220464|3027775 said:
Do they even issue the old gold anymore?

I thought it had to be both - the stone had to have the right proportions by the charts and look nice in the simulation
I believe they do, they probably should not as it appears to have hurt their brand.
Here are good reference charts that the cut Group and OctoNus have put together
http://www.octonus.ru/oct/mss/gia&agspgs.phtml

If the stone in question had say 41.1 pav and 34.8 crown and or with very tight symmetry is might well make AGS 0 on light performance.
But the chances in populations are greater that is would be 41.29, 35.2 and not as good because there are more steepish deepish GIA Ex than shallower stones.

I've lost track of all the reports they're shipping out now. DQDs for RBs, DQRs for RBs without light performance evaluation, DQRs for branded fancies with light performance evaluation, DQDs for fancies...


Thanks for posting those Garry.
 
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