About HCA and VG cut - a discussion?

[Tourmaline]

Hi. I am well aware of the preferences here about cut (I don't need to see stock answers about light performance). I am also aware that angles can change from ideal in both directions, and that they can change to complement each other, thus a brilliant shallow stone or a fiery deep one. So...assuming the price DOES make a less than ideal cut stone worth purchasing, if that stone gets a good score on the HCA, should the HCA be totally disregarded, or do you think it would be worth pursuing further? In other words, do you think the HCA is a tool worth using for stones without triple Ex?

 

[soxfan]

Hi. I am well aware of the preferences here about cut (I don't need to see stock answers about light performance). I am also aware that angles can change from ideal in both directions, and that they can change to complement each other, thus a brilliant shallow stone or a fiery deep one. So...assuming the price DOES make a less than ideal cut stone worth purchasing, if that stone gets a good score on the HCA, should the HCA be totally disregarded, or do you think it would be worth pursuing further? In other words, do you think the HCA is a tool worth using for stones without triple Ex?

I have a 2.04 carat bright and brilliant VG cut shallow stone (I think it's rather shallow, but I am far from an expert) with excellent spread. Scored a 3.4? On the HCA. I got a great deal on it from a family friend and don't regret buying for a second. As a matter of fact, I was out shopping yesterday, and was a little self-conscious of it because it's REALLY sparkly and much bigger than the diamonds most women wear around where I live. My finger size is a 4.5 and it's in a VC halo so it's big and blingy.

There is actually a thread a while back where one of the resident experts did a little analysis of it based on the numbers. [URL='https://www.pricescope.com/community/threads/gia-vs-ags-cut-grading.192169/']https://www.pricescope.com/community/threads/gia-vs-ags-cut-grading.192169/[/URL]

I had my choice between that diamond and one that was an excellent cut and I couldn't tell the difference with my own eyes. Not to mention, the spread on my diamond was larger than the other 2 carat. So I chose mine. I think if the price DOES make a VG stone worth purchasing, it is definitely worth pursuing further. There are members on here who have stones that score between a 3-5 on the HCA and they love them. I'd probably get an ideal scope or an aset image of it to make sure it is going to perform well. While a lot of PS'ers can tell the difference between a VG cut and an EX cut, no one in my social circle can. So I don't care.

So for me, yes, it's worth pursuing further. For many others on here, no it wouldn't be.

 

[JulieN]

Is the hca under 4?

 

[WinkHPD]

Hi. I am well aware of the preferences here about cut (I don't need to see stock answers about light performance). I am also aware that angles can change from ideal in both directions, and that they can change to complement each other, thus a brilliant shallow stone or a fiery deep one. So...assuming the price DOES make a less than ideal cut stone worth purchasing, if that stone gets a good score on the HCA, should the HCA be totally disregarded, or do you think it would be worth pursuing further? In other words, do you think the HCA is a tool worth using for stones without triple Ex?

There are incredible looking diamonds with "horrible" HCA scores. There are crummy looking diamonds with "great" looking HCA scores.

It is a useful tool for deciding which diamonds to look at if you are not working with someone you know and trust to help you look through his/her eyes.

BBBBBUUUUUUUUUUUUUUUTTTTTTTTTTTTTTTTTTTTTTTTTTTT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

You must be able to see, and return if you do not like it, the diamond involved. You can not judge only by paper and you can not judge solely by the tools involved at showing diamonds. YOu can only determine, with YOUR EYES, if you actually like the diamond that you are thinking of buying.

Wink

 

[Dreamer_D]

Hi. I am well aware of the preferences here about cut (I don't need to see stock answers about light performance). I am also aware that angles can change from ideal in both directions, and that they can change to complement each other, thus a brilliant shallow stone or a fiery deep one. So...assuming the price DOES make a less than ideal cut stone worth purchasing, if that stone gets a good score on the HCA, should the HCA be totally disregarded, or do you think it would be worth pursuing further? In other words, do you think the HCA is a tool worth using for stones without triple Ex?

There are incredible looking diamonds with "horrible" HCA scores. There are crummy looking diamonds with "great" looking HCA scores.

It is a useful tool for deciding which diamonds to look at if you are not working with someone you know and trust to help you look through his/her eyes.

BBBBBUUUUUUUUUUUUUUUTTTTTTTTTTTTTTTTTTTTTTTTTTTT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

You must be able to see, and return if you do not like it, the diamond involved. You can not judge only by paper and you can not judge solely by the tools involved at showing diamonds. YOu can only determine, with YOUR EYES, if you actually like the diamond that you are thinking of buying.

Wink

I couldn't have said it better myself! Literally

Ideally every consumer would be able to spend quality time not only with one or two diamonds they are considering buying, but many different stones and cuts to determine where their priorities lie in terms of cut and the other Cs.

For me personally, what I like about MRBs is the perfection in the cut, which for me is reflected by a rather narrow set of proportions and very symmetrical cutting. I think if I was more after spread I would go for an oval or pear rather than a less than ideal MRB.

 

[Tourmaline]

Thanks, Wink. HCA score of 1.6, in the BIC range. Low crown angle. We already bought my diamond last year. It is one that the expert prosumers would turn their noses at because of the crown angle. Because of the 58% table, though, the crown height is decent, and the pavillion angle is just high enough to complement the crown angle nicely. I enjoy reading this forum, but I keep seeing all diamonds outside of Tolk proportions being panned by the prosumers. My diamond is a major reflector. It takes on the color of its surroundings. I have never had another diamond this big (5.01cts), so I don't know how other diamonds (differently cut) would react to surroundings. I love, love, love my diamond outside in indirect natural light. But it really looks different in all lighting situations. I feel like I am reading from the prosumers that ideal cut diamonds look sparkly and amazing in all lighting conditions, but I wonder how true that is. I wonder if the 1.6 on the HCA means anything. The color is (GIA) L, and I wonder if that plays a part in its performance. I love the facet pattern and spread. I really was wondering if a good (1.6) HCA score meant anything or not. When you (Wink) said that there are great stones with bad HCA scores and ugly stones with good HCA scores, that sort of answered the question. Although I think I was wanting to know, more specifically, if people think it's worth it to use the HCA on VG cut stones, or just reject them without doing so, even if the price is extremely attractive.

We all make choices when choosing a stone, and I guess the question is usually: With a given amount of money to spend, how would you balance the 4 Cs? I chose spread, weight and clarity, and I compromised on color and cut.

It's interesting to me that people seem to feel that the only benefit of a MRB is ideal light performance. I like the roundness. And I like the facet pattern if it's not particularly splintery. Mine has a circle of hearts in the middle, face up, and then arrows coming out of that. The lighting in my bathroom is also really lovely for diamond viewing, haha! I, um, sit there and stare at the little hearts, hee hee.

 

[WinkHPD]

If you got a diamond you love, then nothing else really matters. And with an HCA of 1.6 it is definitely a worthy diamond, no matter what the diamond paper says.

When I was working with trying to do a small selection of Value Select diamonds I had several diamonds that would have been rejected by many here because their HCA scores were above 2. One of the very prettiest had an HCA above 4, but to the eye it was incredible. And it was CHEAP. Somehow the cutter mistaked his way into an incredible diamond, or perhaps he was an incredible cutter who made a dog into an outstanding show champion, I do not know. All I know is the diamond did not fit any parameters that I would normally have chosen and it was stunning to the eye. Those treasures are not found by wandering around the net looking at paper, they are found by looking at diamonds.

Wounds like you got a great looking diamond!

Wink

 

[Tourmaline]

Thanks, Wink. I do love my diamond, especially when I spend a few days not reading PS! Hee hee.

Another thing...I have heard so many times about jewelry store lighting vs. other lighting. I have always hated jewelry store lighting. I don't feel as if I can see a diamond at all with those lights. I am definitely a BIC (white light return) person vs a fire person, I guess, though fire is fun in sunlight.

 

[diamondseeker2006]

I just like diamonds to have a near perfect symmetrical cut, regardless of what shape the diamond is. So if I found a steal of a deal on a very good cut diamond, I would just have it recut to better proportions! Win-win for me!

 

[Tourmaline]

I like optical symmetry, too, and my diamond has that. It couldn't get an excellent for symmetry because it has an extra facet on a natural on the pavilion. I thought about having my diamond recut, and I looked into it, but I would lose too much weight and spread! I really enjoy the fact that my diamond is 5.01cts. I never dreamed of having one this big (I was looking at 3.5ish stones), but this one fell into our laps, so to speak (meaning it was really affordable and had so many properties that I wanted).

 

[Karl_K]

The hca is overly lenient on shallow diamonds for use in a ring and slightly overly harsh on steep deeps.
I do hca in my head for every RB report I look at.
Only some of the stranger combos will I actually run it.
When properly applied it can narrow down a long list to a short one with high potential.
Once the list is down to a manageable level then IS/ASET and in person viewing comes into play.
IS/ASET in most cases trumps hca, but in some cases hca can point out issues not shown in reflector images.
My bottom line it does a good job for what it was designed to do, sort large lists of diamonds for further review. It is a rejection tool.
Will it downgrade some nice diamonds? Yes but so will GIA x and AGS0.
Will it give a good score to a dud? Yes, because the numbers are rounded then averaged then in the case of GIA grossly rounded and it does not take into account the minor facets and optical symetry.
But it is not a selection tool so a false positive does not matter if it is properly used.
They will be rejected in the next step.

One way of looking at it is hca tells you if the basics are reasonable then you have to find out if the whole supports them.

 

[LLJsmom]

My first ering was very good in the categories. I forgot. GIA did not have cut grades back then. I love how it sparkles. I don't even know the HCA score.

My current ering stone is very white to me in all kinds of lighting, office, bathroom, shade outdoors. In direct sunlight I see the medium blue fluor. In the dark it seems even whiter to me. I think I prefer brilliance to fire. I don't think HCA is everything. IRL, my moms ring scored a 4 something. But it still looks very sparkly to me. Well, maybe that says I have crappy eyesight.

 

[Dreamer_D]

Tourmaline, what are you after here... You want a general discussion or do you want to discuss and validate your diamond? Because people won't likely participate in a thread that mixes those two intentions... Already I see you taking some peoples comments personally.

ETA and yes, you will almost never see any prosumers on PS recommend a diamond like yours. That's partly because many of us want to make safe recommendations to buyers and the straightest way to that end is to stick with ideal proportions. But so what? I own a diamond with no papers that I bought on eBay. I would also never recommend anyone buy a diamond like that you love your diamond, why be insecure??

 

[Tourmaline]

Dreamer_D, good point. I really wanted people's answers to the question of whether the HCA should be used on diamonds that are VG, as opposed to Ex, or if the HCA becomes not useful in non-Ex cut stones. You're right, though, that I have been trying to justify my diamond, too. Ignore that part, please.

Karl and Wink have given interesting info about the HCA. I am still wondering what the experts think about punching in numbers of non-ex diamonds - does the HCA have the same value on VG stones as it does on Ex stones (in terms of showing which ones deserve further consideration)? I mean...I know that many expert prosumers would not even bother with checking non-ex cut stones, but if they did it, would the HCA score still be valid? I am interested in this question in general, not just because I bought a VG stone.

 

[WinkHPD]

<SNIP>

Wounds like you got a great looking diamond!

Wink

Sigh, proof read much? That was supposed to read, "Sounds like..."

 

[teobdl]

Yes, there are examples of diamonds graded VG by GIA that are nevertheless wonderful diamonds. The best example of this is a diamond cut to great proportions, but it has a thick girdle. I suppose you could use the HCA if you don't have what these proportions are in mind.

Another example is a diamond with proportions that grade 0 AGS but VG by GIA. There is a small segment of diamonds w/ a high crown that meet this criteria. If you look at the bold and dotted lines in the HCA tool's heat map, you'll see what I'm talking about in the bottom right. The HCA tool does not give these diamonds high scores because 1) the HCA creator's preference for shallow crown diamonds (whether justified or not, depending on whom you ask), and 2) the difficulty in cutting these diamonds w/o totally screwing up--search the forums for "cutting cliff"--I imagine that more often then not, diamonds w/ these average proportions stink, but a skilled cutter can make bring everything together to make it just right. Again, these diamonds would be graded VG by GIA but 0 by AGS.

So to answer you question, if you want to find a really nice diamond graded VG by GIA, then sometimes you can use the HCA tool and sometimes you can't. If you suspect that you've found a winner, you almost absolutely need a reflector image verify that all is well... much more so than for a diamond graded Ideal by GIA.

 

[LLJsmom]

Yes, there are examples of diamonds graded VG by GIA that are nevertheless wonderful diamonds. The best example of this is a diamond cut to great proportions, but it has a thick girdle. I suppose you could use the HCA if you don't have what these proportions are in mind.

Another example is a diamond with proportions that grade 0 AGS but VG by GIA. There is a small segment of diamonds w/ a high crown that meet this criteria. If you look at the bold and dotted lines in the HCA tool's heat map, you'll see what I'm talking about in the bottom right. The HCA tool does not give these diamonds high scores because 1) the HCA creator's preference for shallow crown diamonds (whether justified or not, depending on whom you ask), and 2) the difficulty in cutting these diamonds w/o totally screwing up--search the forums for "cutting cliff"--I imagine that more often then not, diamonds w/ these average proportions stink, but a skilled cutter can make bring everything together to make it just right. Again, these diamonds would be graded VG by GIA but 0 by AGS.

So to answer you question, if you want to find a really nice diamond graded VG by GIA, then sometimes you can use the HCA tool and sometimes you can't. If you suspect that you've found a winner, you almost absolutely need a reflector image verify that all is well... much more so than for a diamond graded Ideal by GIA.

Quick question. So can you trust your eyes? If you like the stone and it's beautiful to you, it's all good right? I'm just wondering if there are people who won't buy a stone if the specs are not "right" but they love it's look anyway. Please ignore if this is a thread jack.

 

[teobdl]

Quick question. So can you trust your eyes? If you like the stone and it's beautiful to you, it's all good right? I'm just wondering if there are people who won't buy a stone if the specs are not "right" but they love it's look anyway. Please ignore if this is a thread jack.

Not a thread jack at all. I think this is critical point: find out what YOUR eyes like!

 

[Tourmaline]

Quick question. So can you trust your eyes? If you like the stone and it's beautiful to you, it's all good right? I'm just wondering if there are people who won't buy a stone if the specs are not "right" but they love its look anyway. Please ignore if this is a thread jack.

Certainly not a thread jack! Good question. I think the going belief is that if you compare a non-ideal cut stone with an ideal one, the ideal one will make the other one look terrible. While I'm sure that ideal cut stones do sparkle more than less-than-ideal cut ones, I think some people value that extra bit of sparkle more than others.

 

[Garry H (Cut Nut)]

If you got a diamond you love, then nothing else really matters. And with an HCA of 1.6 it is definitely a worthy diamond, no matter what the diamond paper says.

When I was working with trying to do a small selection of Value Select diamonds I had several diamonds that would have been rejected by many here because their HCA scores were above 2. One of the very prettiest had an HCA above 4, but to the eye it was incredible. And it was CHEAP. Somehow the cutter mistaked his way into an incredible diamond, or perhaps he was an incredible cutter who made a dog into an outstanding show champion, I do not know. All I know is the diamond did not fit any parameters that I would normally have chosen and it was stunning to the eye. Those treasures are not found by wandering around the net looking at paper, they are found by looking at diamonds.

Wounds like you got a great looking diamond!

Wink

Hi Wink, do you remember the stones proportions?
was it loose or set?
Was light able to enter the pavilion when you viewed it?

 

[Karl_K]

Karl and Wink have given interesting info about the HCA. I am still wondering what the experts think about punching in numbers of non-ex diamonds - does the HCA have the same value on VG stones as it does on Ex stones (in terms of showing which ones deserve further consideration)?

Yes.
The crown pavilion angle relationship along with the lower halve/girdle angle and table size define the potential of an RB diamond.
Painting and digging can modify it but not without a compromise in scintillation.
Optical symmetry can also alter it a little.
Tightness of the angle ranges can also have an effect, in some cases large ones.
There are cliffs to avoid over 41.4 is one, color entrapment goes off a cliff at 41.4 degrees with pretty much any crown.
Under around 40.6 in a ring obstruction can be an issue if the crown angle is not steep enough to compensate. I wont argue that a 40.5 pavilion with a 34.5 crown 55t if it is precision cut to tight angle tolerances can be just fine in a ring.
The hca does not catch shallow pavilions, it gives them a good score because they are awesome earring and pendant stones and Garry likes them.

The hca has a bias against 41+ degree pavilions that many old timers and those that learned from the old timers and don't want to relearn anything share.
I suspect this goes back to the days when 41.4 could not be measured, because the tools only measured very roughly to the .5 degree. 41 was good 41.5 has entrapment issues so always stay under 41!
We can measure the angles much more closely today but the bias remains.
Also the lower girdle/halve angles become more critical when you go over 41 degrees.

 

[Tourmaline]

Thank you, Karl! My pavillion angle is 41.2, with a very low crown angle, just FYI. Color entrapment, though...that could be what's going on with my stone - how it reflects the colors around it (takes on the color around it). Is that what that means?

 

[Andelain]

If you got a diamond you love, then nothing else really matters. And with an HCA of 1.6 it is definitely a worthy diamond, no matter what the diamond paper says.

When I was working with trying to do a small selection of Value Select diamonds I had several diamonds that would have been rejected by many here because their HCA scores were above 2. One of the very prettiest had an HCA above 4, but to the eye it was incredible. And it was CHEAP. Somehow the cutter mistaked his way into an incredible diamond, or perhaps he was an incredible cutter who made a dog into an outstanding show champion, I do not know. All I know is the diamond did not fit any parameters that I would normally have chosen and it was stunning to the eye. Those treasures are not found by wandering around the net looking at paper, they are found by looking at diamonds.

Wounds like you got a great looking diamond!

Wink

Do you still have a link for that stone? I'd love a look at it.

 

[Karl_K]

Thank you, Karl! My pavillion angle is 41.2, with a very low crown angle, just FYI. Color entrapment, though...that could be what's going on with my stone - how it reflects the colors around it (takes on the color around it). Is that what that means?

unless a lot of the angles exceed 41.4 degrees it is not likely color entrapment. (remember they are averaged)
Color entrapment means the light bounces multiple times and intensifies the body color.

Showing the color around it just means it is returning light.
This is more obvious in some diamonds proportion sets than others but they all do it.
Can you post all the numbers you have for your diamond and where you got them ie: gia report, sarin scan etc.?

 

[msop04]

This topic is fascinating to me -- thanks Tourmaline!

I am also a an owner of a stone with HCA >2 (I know, I know... "banish me to the maul!!") Maybe Garry, Karl, Wink or another expert can explain why my stone was "dinged" on the HCA.

I have a 2.43 ct GIA XXX (60/60 stone) in a J color that has awesome sparkle and looks really white to my eyes, yet receives 2.7 on the HCA. Here are the specs:

D: 60.1
T: 61.0
CA: 33.5
PA: 41.1

8.7mm

I'm not trying to validate my stone, because I loved it prior to knowing the HCA, and I still love it after... I also got an good deal on it (well, a better than fair deal...) Are 60/60 stones typically scored as such, or is it just how it panned out for mine in particular??

 

[Karl_K]

This topic is fascinating to me -- thanks Tourmaline!

I am also a an owner of a stone with HCA >2 (I know, I know... "banish me to the maul!!") Maybe Garry, Karl, Wink or another expert can explain why my stone was "dinged" on the HCA.

PA: 41.1

Pavilion angle over 41 read my post above where I talk about the 41 degree bias.

 

[msop04]

This topic is fascinating to me -- thanks Tourmaline!

I am also a an owner of a stone with HCA >2 (I know, I know... "banish me to the maul!!") Maybe Garry, Karl, Wink or another expert can explain why my stone was "dinged" on the HCA.

PA: 41.1

Pavilion angle over 41 read my post above where I talk about the 41 degree bias.

Thanks, Karl -- I thought it was >41.4, but must have misinterpreted.

 

[Karl_K]

This topic is fascinating to me -- thanks Tourmaline!

I am also a an owner of a stone with HCA >2 (I know, I know... "banish me to the maul!!") Maybe Garry, Karl, Wink or another expert can explain why my stone was "dinged" on the HCA.

PA: 41.1

Pavilion angle over 41 read my post above where I talk about the 41 degree bias.

Thanks, Karl -- I thought it was >41.4, but must have misinterpreted.

41.4 is where color entrapment actually goes off a cliff. There is a bias in hca and many in the trade with pavilions 41 and over based on the more or less industry tradition.

 

[msop04]

This topic is fascinating to me -- thanks Tourmaline!

I am also a an owner of a stone with HCA >2 (I know, I know... "banish me to the maul!!") Maybe Garry, Karl, Wink or another expert can explain why my stone was "dinged" on the HCA.

PA: 41.1

Pavilion angle over 41 read my post above where I talk about the 41 degree bias.

Thanks, Karl -- I thought it was >41.4, but must have misinterpreted.

41.4 is where color entrapment actually goes off a cliff. There is a bias in hca and many in the trade with pavilions 41 and over based on the more or less industry tradition.

Ahhhh, I see... I guess I saw 41.4 and ran with it in my little head! Thanks for the clarification.

 

[Tourmaline]

Color entrapment means the light bounces multiple times and intensifies the body color.

Showing the color around it just means it is returning light.
This is more obvious in some diamonds proportion sets than others but they all do it.

Oh! Interesting. Here's a visual of that effect.



I am reluctant to post my diamond's numbers, because I am very interested in the topic in general, but I don't want to steer the thread to public scrutiny or justification. I chose the diamond before I knew anything about the HCA or ideal cut details (its HCA score of 1.6 was luck, after the purchase), as it reminded me very much of my mom's diamond (the top one in the following photo), which I always loved. They are very similar!