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GIA Very Good Cut vs Excellent HCA score question

wyprix

Rough_Rock
Joined
Nov 4, 2015
Messages
7
Hi all,

I have been a long time reader of this forum and wanted to start off by thanking everyone for investing their time and sharing their knowledge in enriching this community.

I am posting this thread on behalf of my relative who is in search for an engagement ring for his girlfriend. This is the diamond he is considering: http://www.gia.edu/cs/Satellite?pagename=GST%2FDispatcher&childpagename=GIA%2FPage%2FReportCheck&c=Page&cid=1355954554547&reportno=7182595843

Its cut is only graded as "very good" while the other two are "excellent". The stone scores "excellent" (score 1.1) on HCA, indicating only a weakness in spread. Can I get the community's opinion on this stone? (PS, I know IF clarity is complete overkill and have surely related that to him).

Thank you in advance
 

ChristineRose

Brilliant_Rock
Premium
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Aug 5, 2012
Messages
926
It's because the girdle is too thick. The HCA does not take girdles into account.

I am not sure how the appearance of the stone would be affected, but it will appear small for its weight and your relative should not pay as much as he would for another 1.50.
 

flyingpig

Ideal_Rock
Premium
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Nov 7, 2015
Messages
2,558
This is a good example of HCA limitation; inability to recognize badly cut stones with extreme angles. The stone has no chance for GIA ex because of thick girdle and shallow pavillion angle of 40.2, which can cause significant light leakage.

Try HCA again and see where X is situated on the graph. Clearly outside AGS0 and GIAX boundaries.

You want a GIA X or AGS 0 stone that scores well at HCA. You should never rely on just one screening tool


This stone is no good
 

ringo865

Ideal_Rock
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2,397
HCA is a tool to use ONLY on GIA 3x stones. Not VG, not good. 3x only.
 

Dancing Fire

Super_Ideal_Rock
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32,462
The stone is cut too deep at 62.8%.
 

pfunk

Brilliant_Rock
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770
ringo865|1458685838|4009569 said:
HCA is a tool to use ONLY on GIA 3x stones. Not VG, not good. 3x only.
Are you sure about that? Pretty sure it is for any round but it makes a couple of assumptions. One assumption is a symmetrical stone and another is for a medium thickness girdle. Aside from that I am not aware that it can only be used on 3x stones and don't think that is the case. But I've been wrong before.
 

ringo865

Ideal_Rock
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Pfunk, you are right. I must have been thinking that because many PSers don't recommend anything but GIA 3X. It seems the HCA should still score appropriately as long as it has the medium girdle. Sorry all :silenced:
 

pfunk

Brilliant_Rock
Premium
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770
No problem! Just wanted to make sure we had it straight for the OP. Often times when someone is on a tight budget or their wants are not in line with their budget, I specifically look at very good cuts that have a thick girdle but all the right angles. It won't detract from a visual standpoint but will drop the diameter some. However, it will come at a discount because it isn't 3x. As long as the consumer is aware of this these can be a good option.
 

wyprix

Rough_Rock
Joined
Nov 4, 2015
Messages
7
Thank you all for your clarification on HCA! We have a better understanding on how to further narrow down candidates.
 

yssie

Super_Ideal_Rock
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21,255
Super shallow pavilion - it'll be a black slate IRL when you lean over it (over-obstruction), and I wouldn't be surprised if it shows girdle reflection under the table at very slight tint w/ that shallow pav, larger table, and thicker girdle - esp if longer lgfs.
 

Texas Leaguer

Ideal_Rock
Trade
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Jul 27, 2009
Messages
3,320
A good example of the extent to which a cutter is incented to retain a magic weight. If the GIA cut grading system did not reward that make with a "very good" grade, you would probably have seen the diamond become a beautiful 1.35!
 

Wink

Ideal_Rock
Trade
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May 3, 2001
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7,516
pfunk|1458690498|4009601 said:
ringo865|1458685838|4009569 said:
HCA is a tool to use ONLY on GIA 3x stones. Not VG, not good. 3x only.
Are you sure about that? Pretty sure it is for any round but it makes a couple of assumptions. One assumption is a symmetrical stone and another is for a medium thickness girdle. Aside from that I am not aware that it can only be used on 3x stones and don't think that is the case. But I've been wrong before.
It is nice to see you posting again PFunk, I have missed you for a while.

As you already know the HCA is a rejection tool, not a selection tool. It can, as you correctly say be used on any round diamond and give some good insights into some diamonds and lousy insights into others. In this case the HCA grade is influenced by Garry Holloway's preference for shallow diamonds, but not this shallow. With the spread of a 1.40 ct diamond, assuming that that spread could be kept while salvaging a decent pavilion angle, which it can not, this stone is to me over rated even as a Very Good. It clearly was cut to maintain the price break weight of 1.50 cts and is much more expensive even as a poorly cut diamond at a 1.50 ct than it would be as a properly cut stone of lesser weight. Texas Leaguer has suggested a 1.35ct weight. I do not have time to go estimate a good recut weight for this diamond, but I agree with Texas Leaguer that it would be certainly no larger than his suggested weight and would have less cost. It certainly would have GREATER VALUE to the client in terms of beauty for his fiance' but would bring less money to the cutter, who could afford to pay more for the rough knowing he was going to "cheat" the diamond to the 1.50 ct weight. Thus that diamond was lost to those who would cut it correctly but have to pay less for the starting crystal, knowing what it would be worth at the 1.35 ct (or less) weight.

It is often so sad what cutters will do to a diamond crystal in the hunt for the highest price, rather than the greatest beauty. As a business man I can make myself understand that when cutting thousands of stones per month and gaming the GIA cut grading system to make weight savings of even 5% can be worth millions of dollars. When you look at a stone like this, where the weight savings was at least 11% and the price increase, assuming no discount for the poor cutting or premium for proper cutting, a whopping 45% for this color and clarity grade. In real life that premium is probably closer to 20%, but that is A LOT of incentive to "cheat" the cut.

It is also probably why the vendors of such diamonds never offer buy back programs or have trade up policies demanding at least double the original cost. Who wants to ever own such a dog again?

Just my thoughts.

Wink
 

flyingpig

Ideal_Rock
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2,558
wyprix|1458765247|4010030 said:
Thanks again for all the replies!

We have the following candidates and was wondering if we can get some input.

1. BN Signature Ideal (1.11ct, E, VVS2)
http://www.bluenile.com/diamond-details/LD06739495

2. Whiteflash ACA (1.11ct, H, VS2)
http://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3596838.htm

Essentially, my cousin is wondering if the bump in colour grade and clarity is worth the extra $1800 USD.
Normally, I would say ACA. But that BN signature. It has bigger spread. love the proportions... 1.8k for 3 grade up in color, 2 grade up in clarity. Very tempting.. Can't decide....
 

Diamond_Hawk

Brilliant_Rock
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1,221
flyingpig|1458765992|4010040 said:
Normally, I would say ACA. But that BN signature. It has bigger spread. love the proportions... .
I agree with most of what has been said above, but I would advise the OP that more information is needed than just “proportions.” Like others here, I maintain that numbers in a certain range can be promising. But that is not the end of the story. As an example, “pavilion angle” on a grading report is a single number that stands for eight separate measurements. Same with crown angle, same with stars. “Lower halves” stand for 16 and the upper girdles (16 of them) are not even reported. Within the numbers there can be wild variations which create reduction of light return, leakage and dead zones in the diamond.

As time goes on we are seeing more diamonds showing “nice proportions” on their GIA reports, but they have crazy deviations inside the numbers. It is really not a surprise, since manufacturers are learning to “game” the system: If a diamond has a knot which limited blocking to 41.3 degrees on one pavilion main, a clever producer can insist on an overpolish on the other side to 40.3. Why? Because the average will work out to 40.8, which becomes printed on the grading report. It looks good to those analyzing proportions, but there’s trouble inside the numbers.

For this reason I like to encourage getting an ideal-scope or ASET image. It helps reveal what is behind the surface-numbers which are reported.
 

wyprix

Rough_Rock
Joined
Nov 4, 2015
Messages
7
Just wanted to update and close this thread with a ring shot of my cousin's final choice. He went with the BN Signature Ideal in the end. The ring on her finger is stunning! Thank you all for the input and taking the time to answer our questions!

img-20160418-wa0018.jpg
 
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