HCA Score Concerns

[Himmstress]

I am presently choosing between three diamonds that are all GIA triple X 1.2 carat stones and that I have seen in person. The first one is a G, VS2 and rates a 1.8 on HCA. In person it was pretty, but out of the spot lights it seemed to show the least amount of fire. The second one is an F, SI1 (eye clean) and rates a 3.4 on HCA. The third is an F, VS2 and rates a 5.5 on HCA. I found out the HCA score for the F, VS2 before going to see that stone and had decided that I could not choose it because of the low score. However, in person, the F, VS2 seemed to show more sparkle to it (more rainbow colors bouncing back) when it was in the shadows and in natural sunlight. Being a scientist, it scares me to choose a stone with an HCA of 5.5. I realize that it is still an excellent cut by GIA standards, and purchasing a diamond is really based on personal preference over calculations; but should I revert to the F, SI1 with the HCA of 3.4, which showed a tad less sparkle factor to my eyes? The specs for each stone is below. Cost between the three is not a factor in this decision. I just don't want to purchase something that most others would find less attractive.

F, VS2
Measurements - 6.75 - 6.80 x 4.25 mm
1.2 carat
F color
VS2 clarity
Excellent cut grade
Excellent polish
Excellent symmetry
No Fluorescence
Table 58%
Crown Angle 36%
Pavillion Angle 41.2%
Depth 62.7%
Star length 55%
Girdle medium-slightly thick faceted 3.5%
Crown height 15%
Pavillion depth 44%
Lower half length 80%
No cutlet

F, SI1
Measurements - 6.81 - 6.84 x 4.19 mm
1.2 carat
F color
SI1 clarity
Excellent cut grade
Excellent polish
Excellent symmetry
No Fluorescence
Table 59%
Crown Angle 34.0%
Pavillion Angle 41.2%
Depth 61.3%
Star length 50%
Girdle medium-slightly thick faceted 4.0%
Crown height 13.5%
Pavillion depth 43.5%
Lower half length 75%
No cutlet

G, VS2
Measurements - 6.78 - 6.82 x 4.18 mm
1.2 carat
C color
VS2 clarity
Excellent cut grade
Excellent polish
Excellent symmetry
No Fluorescence
Table 59%
Crown Angle 34.5%
Pavillion Angle 40.8%
Depth 61.5%
Star length 50%
Girdle medium-slightly thick faceted 4.0%
Crown height 14.5%
Pavillion depth 43.5%
Lower half length 80%
No cutlet

 

[JulieN]

58 and 59% table size is by no means large, but you could easily find smaller-tabled, higher-crowned diamonds than the three you listed with good HCA scores. Perhaps if you pulled the table down to 56 and below, and a crown height of at least 15%, that would have the desired effect.

 

[Himmstress]

Thanks Julie. Would you suggest against selecting one of the two F colored stones based on their HCA scores? I guess I am unsure how relevant a poor score is with respect to what the eye sees? The F, VS2 was super sparkly, and if I had never researched the HCA score, I would have felt totally okay with selecting that stone. But does the score of 5.5 mean something bad?

 

[JulieN]

Since you were sensitive enough to pick out the difference between 1, 2, and 3, I feel confident that you will be able to identify the difference between #1 and and an ideal cut of Tolkowsky-style proportions.

 

[Himmstress]

So it sounds like you are indicating that an HCA score of 5.5 is a bad thing, despite it looking nice in person? If it is a bad thing, should I have seen the stones that scored a 1.8 and a 3.4 as better than the 5.5 in that case? If I saw the 5.5 as being the most sparkly, could you help me understand what a change in the HCA score to a better one should yield in terms of what I would see visually? I am working with a local jeweler, who doesn't have any exciting scopes for me to look at the diamond. If I wanted to get more information on the diamond, what would be the easiest thing he could provide to me in terms of cost and work from his end? Would a Sarin report be helpful in this case to see if the 5.5 is inaccurate? Or should I ask for something else? I feel bad, because these stones he is showing me are presently on loan from his diamond guy and he indicated he has a finite amount of time to keep the stones before they have to go back. I understand I am the consumer, but I don't want to draw this process out too horribly long and gruelingly for either of us.

 

[diamond-enthusiast]

Get a Sarin and post it here. There are limitations to the Sarin though. It only tells you how precisely the facets are cut. But doesn't tell you the relationship between angles and light performance.

 

[JulieN]

A Sarin will not tell you anything useful. GIA's calibration of their machines should be better than those maintained elsewhere. Also GIA's machines should be a high-end model with better precision. Disregarding accuracy and precision, the best case scenario for the numbers given is a 35.8/41.1 combo, which yields a 5.1 HCA. Broad usage guidelines for HCA: less than 2 is predicted to be "excellent," follow up with Ideal-Scope or see in person. 2-4 with excellent symmetry is predicted to be "very good," with good symmetry these stones may be as attractive as one that scores <2, but you should follow up with an Ideal-Scope and trusted vendor if buying online, or see for yourself next to an ideal cut. 4+ gives you the mesage "only if price is your main concern." These largish-table steep/deep combos are weight-retaining and they should not cost as much as a Tolk-style.

There is no reason to feel bad for your vendor, borrowing/loaning diamonds "on memo" is the standard industry practice. IMO if the stones are recalled, then so be it, there is no need to feel pressured to make a decision based on that.

Diamonds with poor cut are still sparkly, or else no one would buy the typical radiant that leaks like a sieve, but people do, all the time. If you did not perceive the other two as more attractive, that's ok, brightness isn't everything. Basically, the proportions that yield a 5+ HCA are predicted to have visible leakage. Leakage means light that goes in does not come out, a small amount of loss is normal.

Though beauty is difficult to define and convey, from what you have posted you may benefit from comparing it to a Tolk-style ideal cut, or a FIC (which has crown angle of <=36, like #1, but with complimentary proportions.) Once you compare them you might still prefer the original, but at least you will have made a better informed decision. In my experience men posting on PS about diamonds with HCA of 5+ tend to be attracted to the price, or that was what their jeweler had to show them. They either take our advice to compare to an ideal cut, and then say that the ideal cut was the clear winner. Or in one case, IIRC he bought the 5+ stone and boast about the good deal he got in comparison to suggestions that PSers make for him, and then proceeded to post pictures of a visibly leaky diamond.

 

[Himmstress]

Thanks for all the info Julie. I'm actually female in this case. My boyfriend is just ready to pay the bill and less interested in the process The 5.5 HCA diamond was actually $1,800 more than the 3.4 HCA diamond and and $1,200 more than the 1.8 HCA diamond. I think that was based on it being the better clarity combined with the better color. I think I will call the jeweler back to see if I can see one with a lower HCA number. Can you explain the difference between a TIC, an FIC, and a BIC in terms of what I would see when I look at them? I really liked the rainbow colors that I saw coming out of the 5.5 diamond a lot, so what would be good for that? The jeweler had never heard of HCA, but his diamond dealer had. If I talk to the jeweler, what do you suggest I specify to him regarding the HCA? A set of approximate proportions or ask him to have the dealer find one with a low HCA score? And is it worth going down in carat size a little bit in order to get a better HCA scoring diamond? Or maybe I should look into seeing if I can get an F, SI1 with a good HCA and stay around 1.2 carats?

 

[JulieN]

The B in BIC stands for bright. Then we have Tolkowsky and firey. HCA carries some informative fine print:

Deeper proportioned stones, near the upper part of the red area, have more leakage. Leakage means reduced light return. A limited amount of reduced light return can contribute to a diamonds contrast. Diamonds with a large area of partial leakage table, seen as a pale pink area with an Ideal-Scope, are best set in open backed rings so light can get in the bottom or pavilion of the diamond. It is possible for light entering the pavilion to leak back out the top as firey dispersed colored flashes. Deeper diamonds that have perfect or hearts and arrows grade symmetry, with scores around 2, will often perform far better than diamonds of lesser symmetry.

You might read this. I would skip the pages on painting/digging, though: http://www.goodoldgold.com/4Cs/NewCutGrading/

I would ask to see AGS 0 or GIA EX with ~56 and below table, crown height 15+, with HCA under 3.

 

[Himmstress]

The jeweler is bringing in another stone for me to take a look at that has proportions that would be closer to 0-2 on the HCA. But I was wondering if anyone here might be able to help me out with running modeled Ideal-Scope simulations for the three stones that I have already looked at. It might be helpful for me to see.

 

[TC1987]

This is the highly, highly condensed version: https://www.pricescope.com/wiki/diamonds/diamond-crown-and-pavilion
TIC cut for a good balance between brilliance (white light) and fire (dispersion.)

BIC Larger table, lower crown angles, less %of the total depth is the crown. Many "60/60" diamonds fall into this category. Flashes of white light (brilliance) are what you see from across the room, though.

FIC steeper crown angle 35-36 or more, with a smaller table. Lots of fire = less white light reflected back, so these diamonds sometimes look "dark." But very fiery. More % of the overall depth is crown height. Some of the FICs might face up a bit small for carat weight.

NiceIce dotcom used to be a Pricescope vendor, but now he just runs an information site. These are his very tight ranges for picking the best-cut diamonds. Crown and pavilion have to be balanced with each other: A steeper crown angle needs a shallower pavilion angle, and vice versa, or you get leakage. The symmetry is what produces scintillation and contrast. His explanations are concise, if you just want to scan-read something fast.
Total depth between 59 – 61.8%
Table diameter between 53 – 57.5%
Crown angle between 34.3 – 34.9 degrees
Pavilion angle between 40.6 – 40.9 degrees
Girdle edge between 0.7% thin to medium
Culet: GIA “none” or AGS “pointed” (same thing)

I bought three of my diamonds online, two from Good Old Gold. I found that the local stores just didn't get the same caliber of cut, and if they had to order it and add their store markup, the prices were far higher than buying from GOG or WF, Brian Gavin, etc.