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»  » Diamond Prices and Grading »
 » RockyTalky
»  » How do your stones rate on the HCA?
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| Pages: 1 of 2: [1] 2 > |
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How do your stones rate on the HCA? |
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| P: 12/21/2003 12:27:22 PM | |
Manks Rough Rock Total Posts: 78 Last Post: 12/20/2004 Member Since: 11/30/2003 |
Hi All How many of you have run your stones through the HCA? All of you I'd guess. What are your scores?
Manks |
| Posted: 12/21/2003 12:27:22 PM | |
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There are 35 replies to this message. There are 30 replies on this page. |
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| P: 12/21/2003 2:50:25 PM | |
stephcola Cut Rock Total Posts: 116 Last Post: 5/16/2005 Member Since: 10/3/2003 |
Hi Manks.
Never heard of the HCA before Pricescope but as soon as I heard, I put every stone' s numbers into the cut advisor. I now have a 3.01 ct. H SI1 - HCA score 1.2 FIC. Cheers!!!
stephcola |
| Posted: 12/21/2003 2:50:25 PM | |
| P: 12/21/2003 3:01:50 PM | |
canadiangrrl Ideal Rock Total Posts: 787 Last Post: 3/19/2008 Member Since: 6/10/2003 |
Mine rated 1.8 TIC (EX/VG/VG/VG) when I used the angles from the AGS DQD, and 1.0 TIC (EX/EX/EX/VG) when I used the angles given to me by the gentleman who appraised my stone, Rich Sherwood. A slight change in the pavilion angle can make a huge difference on the HCA. Sursum Corda! |
| Posted: 12/21/2003 3:01:50 PM | |
| P: 12/21/2003 3:15:41 PM | |
Mara Ideal Rock Total Posts: 27,922 Last Post: 11/23/2009 Member Since: 10/30/2002 |
In Nov 2002 when we got our stone, it rated a 1.5 BIC with something like EX VG VG EX.
In Feb 2003 when Garry made some changes to the HCA...it rated a 2.3 VG with something like VG VG VG EX.
And now whenever the last changes were made (sometime after Feb) to today, it rates 2.8 VG VG G EX.
 Confused yet? Funny add is that to be really honest, if the stone had rated the 2.8 in Nov 2002 when we bought it...we wouldn't have gotten it. It was up against another stone, that was actually pretty 'ideal' in terms of numbers that rated 1.0 TIC EX EX VG EX or similar and we went with the stone we have now because the HCA score was still excellent and was much bigger with diameter due to the shallow proportions.
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| Posted: 12/21/2003 3:15:41 PM | |
| P: 12/21/2003 3:19:30 PM | |
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Manks Rough Rock Total Posts: 78 Last Post: 12/20/2004 Member Since: 11/30/2003 |
Mara Mine too. I bought when I knew nothing at all and am pleased that the stone I bought is even on the scale! I am sure that the majority of stones bought in rings across the counter would rate very badly. Manks |
| Posted: 12/21/2003 3:19:30 PM | |
| P: 12/21/2003 3:27:14 PM | |
Petunia Rough Rock Total Posts: 56 Last Post: 12/28/2008 Member Since: 6/10/2003 |
Manks The diamond we purchased back in May of this year scored 1.3 on the HCA. It looked great to me then as it does now. Lately, however, I wish I had compared it to a 0.5 to see if there was any discernable difference between the two. Just a curiosity thing  I am happy with what I have.Helen |
| Posted: 12/21/2003 3:27:14 PM | |
| P: 12/21/2003 4:54:38 PM | |
lop Ideal Rock Total Posts: 2,651 Last Post: 9/7/2009 Member Since: 6/14/2003 |
My new e-ring stone is 1.6 TIC EX,EX,EX,VG. I don't have crown or pav measurements on any of my other stones to run through the HCA, but my bet is they wouldn't score well -- they all look as if they have large tables. (must be the "let's make it look as big as possible deal" and were all purchased years ago pre-pricescope and Internet diamond education.) I too am curious about how a 1.6 would compare visually to a .6 (we considered one, but it sold before we were ready to move).
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| Posted: 12/21/2003 4:54:38 PM | |
| P: 12/21/2003 5:45:31 PM | |
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Mara Ideal Rock Total Posts: 27,922 Last Post: 11/23/2009 Member Since: 10/30/2002 |
Something to note is that anything .5 or under may not be as good-looking as say something above, because under .6 you start to see a loss of contrast which is essential for the stone to scintillate while being moved. Reds and blacks if you will. So if your stone is something like a 1 TIC or a 1.5 TIC chances are comparing it to a .5 or similar would only make your stone look better
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| Posted: 12/21/2003 5:45:31 PM | |
| P: 12/21/2003 6:53:33 PM | |
aljdewey Ideal Rock Total Posts: 8,236 Last Post: 2/11/2008 Member Since: 11/25/2002 |
My new engagement ring rates a 0.9 - ex-ex-ex-vg.
My cheapo earrings from Zales - probably rate a 20! UGH. (Didn't know any better then.
)_____________________ |
| Posted: 12/21/2003 6:53:33 PM | |
| P: 12/21/2003 7:08:16 PM | |
MC Ideal Rock Total Posts: 8,848 Last Post: 11/23/2009 Member Since: 2/8/2003 |
I've never run my eng. ring through the HCA since it's set and i only have the table and depth numbers. Next stone purchase will be run through for certain! Michelle
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| Posted: 12/21/2003 7:08:16 PM | |
| P: 12/21/2003 7:35:41 PM | |
derekinla Cut Rock Total Posts: 467 Last Post: 6/16/2005 Member Since: 9/8/2003 |
My Fiance's 1.4 Carat G SI1 has an HCA of 0.3 (Ex Ex Ex Ex)
Derek in Los Angeles |
| Posted: 12/21/2003 7:35:41 PM | |
| P: 12/21/2003 7:47:51 PM | |
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Butterfly17 Ideal Rock Total Posts: 678 Last Post: 6/13/2006 Member Since: 1/14/2003 |
When I use my TIC diamond's AGS measurements I get 1.1. When I use the Sarin from Whiteflash I get 1.0. When I use the Sarin from AGA I get 1.0. "I'm a Brat" - Mara (PS Queen) |
| Posted: 12/21/2003 7:47:51 PM | |
| P: 12/21/2003 9:59:21 PM | |
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stephcola Cut Rock Total Posts: 116 Last Post: 5/16/2005 Member Since: 10/3/2003 |
Canadiangrrl,
I too had my stone evaluated by Rich Sherwood. I was so happy he gave me a great report that I did not run his numbers through the HCA. One number (and I cannot remember which) was ever so slightly different. Rich's appraisal is now in the vault and I am curious!!! It is Sunday night and I know I will not get to the vault this week. I am interested to see if there is any difference. I know it will bug me all week!! Regards,
stephcola |
| Posted: 12/21/2003 9:59:21 PM | |
| P: 12/21/2003 10:18:24 PM | |
abbymax825 Rough Rock Total Posts: 76 Last Post: 10/5/2004 Member Since: 12/21/2003 |
So I'm obviously new at all of this and trying to learn as much as I can. What is the HCA and what nubers do you need, where do you find it to input the numbers if you have them. What does the Ex, ex ex ex all mean. I know it is excellent but what about the diamond is it describing. If no one wants to take the time in explaining, there must be a web site somewhere???
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| Posted: 12/21/2003 10:18:24 PM | |
| P: 12/21/2003 10:38:02 PM | |
Patty Ideal Rock Total Posts: 4,031 Last Post: 6/4/2008 Member Since: 12/7/2003 |
abbymax, At the top of the page you will see a link to "cut adviser." This is the Holloway Cut Adviser which was designed to give you an idea as to the quality of the cut of your diamond. You need your stone's measurements including the angles to put into the formula and then it gives you your result. It says on the site that anything below a 2 (or was it 3?) is very good.
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| Posted: 12/21/2003 10:38:02 PM | |
| P: 12/21/2003 11:18:51 PM | |
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canadiangrrl Ideal Rock Total Posts: 787 Last Post: 3/19/2008 Member Since: 6/10/2003 |
And just to add to Patty's remarks - the HCA will presently only work for round brilliant diamonds.
Sursum Corda! |
| Posted: 12/21/2003 11:18:51 PM | |
| P: 12/21/2003 11:48:00 PM | |
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Petunia Rough Rock Total Posts: 56 Last Post: 12/28/2008 Member Since: 6/10/2003 |
Mara, Does this stone explain what you describe? http://www.goodoldgold.com/1_42ct_f_vs1_AGS000.htm When I plugged the numbers into the HCA, it returned a score of 0.5 ex ex ex ex. Yet when you look at the Isee2 results: 7.7, and the Brillianscope results: Med, Very High, High/Very High. This is not what I would have expected from a 0.5 score. But now I see that that a low score does not equal exceptional performance on these tests. Of course, visually the stone may be very appealing. Then again, it might not. Beauty is in the eye of the beholder (or as my friends would say, beer holder ) Helen |
| Posted: 12/21/2003 11:48:00 PM | |
| P: 12/22/2003 1:35:04 AM | |
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Mara Ideal Rock Total Posts: 27,922 Last Post: 11/23/2009 Member Since: 10/30/2002 |
Possibly Petunia...maybe one of the experts can chime in on the low HCA scores and contrast. I used to think super low was best but I guess not. Also, if you note on the HCA itself, Garry says that 'your personal preference may be for a diamond with a score of 1.5 instead of 0.5'...that must have something to do with this as well.
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| Posted: 12/22/2003 1:35:04 AM | |
| P: 12/22/2003 2:46:21 AM | |
Toska Cut Rock Total Posts: 114 Last Post: 7/7/2004 Member Since: 11/3/2003 |
Mine scores VG/EX/EX/EX HCA=1.3 What sort of stone scores in the FIC or BIC range? Why is it that most people scores for spread/diameter, are VG as opposed to excellent? I've seen about 80% of stones score a VG in this category while all of the others vary. 
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| Posted: 12/22/2003 2:46:21 AM | |
| P: 12/22/2003 2:48:56 AM | |
QueenMum Ideal Rock Total Posts: 1,971 Last Post: 10/28/2009 Member Since: 2/13/2003 |
The best diamond I have is a 0.8 TIC, EX-EX-EX-EX. It looks better than all my other diamonds. Stephan |
| Posted: 12/22/2003 2:48:56 AM | |
| P: 12/22/2003 2:58:45 AM | |
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Mara Ideal Rock Total Posts: 27,922 Last Post: 11/23/2009 Member Since: 10/30/2002 |
Toska, most of the stones are like this when run through HCA (VG vs EX for spread).
Seems that mostly only the stones like BIC or similar get EX for spread though I have seen a few TIC's get it as well. Spread being EX would seem to require it looking bigger than a typical same size stone...so maybe that area of rating in the HCA is more strict.
I tend to look at the other 3 designations more when I run the #'s and if a Spread = EX then I am pleasantly surprised, but it doesn't seem to be the rule, rather the exception.
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| Posted: 12/22/2003 2:58:45 AM | |
| P: 12/22/2003 3:11:07 AM | |
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Toska Cut Rock Total Posts: 114 Last Post: 7/7/2004 Member Since: 11/3/2003 |
As I previously mentioned my stone scores VG/EX/EX/EX It has a table of 59.7, I notice that when I plug in 59.6 it scores EX in all of the categories, therefore I believe it is almost 4 excellents, how much difference can 0.1 of a degree significantly make? 
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| Posted: 12/22/2003 3:11:07 AM | |
| P: 12/22/2003 5:09:14 AM | |
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Manks Rough Rock Total Posts: 78 Last Post: 12/20/2004 Member Since: 11/30/2003 |
Mine scores VG/EX/EX/EX HCA=1.3 What sort of stone scores in the FIC or BIC range? Why is it that most people scores for spread/diameter, are VG as opposed to excellent? I've seen about 80% of stones score a VG in this category while all of the others vary. Now then, let me see if I can explain that: Spread is a positive characteristic, and a stone increases in spread with increased table size. The reason that spread is important is not for reasons of performance, it is because it makes the stone look bigger - i.e. you are getting a bigger looking stone for your money. Most uninformed buyers and many informed ones, it appears, prefer a stone with good spread for this reason. The other measures on the HCA are directly about performance, i.e. Light return, fire and scintillation. All of these measures are INCREASED by REDUCING table size from that which will give best spread, because a larger table reduces these properties in a diamond. The practical upshot of this is that a stone with a low score (i.e. high rating) on light return, fire and scintillation will tend to score lower on spread, whereas a stone with good spread will be compromised on the other three measures. I am not an expert, if anyone who is would like to improve on that explanation, please feel free. Manks Manks |
| Posted: 12/22/2003 5:09:14 AM | |
| P: 12/22/2003 5:13:51 AM | |
Garry H (Cut Nut) Ideal Rock Total Posts: 11,582 Last Post: 11/24/2009 Member Since: 8/16/2000 |
Puuuurrrr fect Manks 
Garry Holloway FGAA DipDT |
| Posted: 12/22/2003 5:13:51 AM | |
| P: 12/22/2003 4:48:24 PM | |
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Toska Cut Rock Total Posts: 114 Last Post: 7/7/2004 Member Since: 11/3/2003 |
Garry, Would you be able to let me know if 0.1% in table size is that much of a difference to visually affect a diamond. 0.1% in table size is the difference between my diamond scoring an excellent in light return as opposed to the Very Good it gets. Is there any upper/medium/lower range of Very Good on the HCA? Or to put it simply, a VG is just a VG, not matter if it is 0.1% away from Excellent or Good? What is your interpretation of these scores, can they be broken down any further?
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| Posted: 12/22/2003 4:48:24 PM | |
| P: 12/22/2003 5:28:47 PM | |
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Garry H (Cut Nut) Ideal Rock Total Posts: 11,582 Last Post: 11/24/2009 Member Since: 8/16/2000 |
if you read about this at www.diamond-cut.com.au you will see that .1% is right on the cusp of a numerical rounding. 1.99 vs 2.00 Toska Garry Holloway FGAA DipDT |
| Posted: 12/22/2003 5:28:47 PM | |
| P: 12/22/2003 5:53:10 PM | |
Rhino Ideal Rock Total Posts: 4,865 Last Post: 11/22/2009 Member Since: 3/29/2001 |
Just some comments....
I would not agree with the assessment that larger table = greater spread. This is not the cast all the time. I can show ya diamonds with >60 tables that have yucky spread.
The HCA cut off for "excellent" spread is 60.3% so if the stone has 60.4 it will not get excellent. Why 60.4?... no logical reason that I can think of because you can have a beautifully proportioned diamond with a depth of 60.4-62 and be way more beautiful than a diamond with a 60.3% depth or less.
My point is, while it is interesting to know it is not a factor in determining diamond beauty.
In the coures of my studies on diamond beauty and optics it seems that both ends of the AGS "Ideal" range lack in one area or another. In the steep/deep combos within the AGS "0" there is the obvious "ring of death" ie. an undesireable ring of light leakage under the table but when we go to the opposite end of that spectrum, the shallow/shallow end of the AGS spectrum I have been finding equally disatrous results using the technologies we use. The shallow/shallow combinations are similar to what our posted referred to above which generally have pavilion angles ranging from 40.2 - 40.6 coupled with crown angles in the low 34's and high 33's. These kind of stones do get very low (and seemingly great) HCA scores but IMO are not the most optically pleasing stones. This is why I would stress (to anyone truly concerned with the diamonds optical properties) that an optical analysis be performed. Of course if I had to choose between a steep/deep vs a shallow/shallow I'd go with the shallow/shallow but would choose neither if I had the opportunity to throw another into the fray like a 34.x/40.7-40.9.
My .02c
Rhino |
| Posted: 12/22/2003 5:53:10 PM | |
| P: 12/22/2003 6:34:38 PM | |
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Toska Cut Rock Total Posts: 114 Last Post: 7/7/2004 Member Since: 11/3/2003 |
---------------- I understand Garry, but my question still remains unanswered...
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| Posted: 12/22/2003 6:34:38 PM | |
| P: 12/22/2003 8:31:13 PM | |
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Garry H (Cut Nut) Ideal Rock Total Posts: 11,582 Last Post: 11/24/2009 Member Since: 8/16/2000 |
Then read it again till you understand Toska IT is all there Garry Holloway FGAA DipDT |
| Posted: 12/22/2003 8:31:13 PM | |
| P: 12/22/2003 9:24:49 PM | |
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Toska Cut Rock Total Posts: 114 Last Post: 7/7/2004 Member Since: 11/3/2003 |
I've read it all before, would you be so kind to provide a link to the exact section which speaks about the 'cusp of numerical rounding'?
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| Posted: 12/22/2003 9:24:49 PM | |
| P: 12/22/2003 10:00:27 PM | |
strmrdr Ideal Rock Total Posts: 23,296 Last Post: 10/9/2009 Member Since: 11/1/2003 |
You have to remember that the hca is a tool nothing more nothing less. Like any other tools it has its flaws. The ags rating system is another tool. Between the 2 I think that hca is a better tool and study of Rhino’s results for his diamonds will possible prove that. But like the gia that is trying to reduce the calculations needed to come up with the perfect shape to 8 for something that would need 1000s if not 100000s of parameters it doesn’t take everything into account. For example it does not take the size and shape of the facet meet points into account. One diamond with perfect sharp meet points and one with rolled meet points could have the same hca score but would look very different. Same thing for varied individual facet angles. Rhino’s optical test results would pick these up because they make a huge difference in appearance but the hca that just uses an average would not. I could go on but I wont at this time because you should get the idea. ........... Karl has joined the diamond trade and is now posting as Karl_K |
| Posted: 12/22/2003 10:00:27 PM | |
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