HCA sensitivity (how much diff. will you see?)

[glt4392]

I have been using the HCA and some of the stones I have seen with agsl 0 cut stones, H&A and GIA excellent symetry and polish vary a lot. In fact, a stone that was not ideal cut scored a .9. Another ideal scored a 1.9, and the last stone I have plugged in which is agsl 0,excellent, excellent GIA polish and symetry and H&A scored a 3.2. Now since this is a "cut" driven forum and very rightly so, how sensitive is this tool? If I have an ideal cut stone which scores a 3 and a non ideal that scores a 1 is the difference in brilliance and shine noticeable to the eye of a consumer and not a stone collector? Or is this more like the disclaimer says a tool to make final decisions with or more for the ones looking for a stone they can measure in fancy machines when no difference may be seen if we are talking about 2 close stones (a 2 and a 2.5 or so forth)
thanks

 

[Stephan]

The HCA is a very nice tool, but the beauty of your diamond depends on the minor facets too, not only on the main crown and pavilion angle...

 

[Stephan]

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On 7/21/2003 5:56:45 PM glt4392 wrote:

If I have an ideal cut stone which scores a 3 and a non ideal that scores a 1 is the difference in brilliance and shine noticeable to the eye of a consumer and not a stone collector?
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I think that you will see the difference between 3 and 1, believe me...

 

[glt4392]

Stephan,
If an ideal cut stone, GIA excellent/excellent (sarin report with all 0) with unbranded H&A gets a 3.2 and a non ideal gets a .9 and you are saying that I will see a difference what does that say about the level to which everyone here pushes the ideal cuts, excellent/excellent and H&A stones when by your statement stone with a very good cut stone that is not ideal you can get a .9 and again by what you said, "You will see a difference..."?

 

[Stephan]

A diamond that scores 3.2 is not an ideal cut, even if it's AGS-0.

 

[Stephan]

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On 7/21/2003 6

9:41 PM glt4392 wrote:

Stephan,
If an ideal cut stone, GIA excellent/excellent (sarin report with all 0) with unbranded H&A gets a 3.2...
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Can you tell me the proportions of your 3.2 ideal cut?
It seems VERY difficult to find such a bad AGS-0...

 

[smaggard]

Also keep in mind that the crown and pavilion angles you are entering are AVERAGES. So you put in crown angle of 34.3, when the rock may have crown angles from 34.2-34.4 and so on.

Also keep in mind the give or take between instruments. A stone may show an average crown angle of 34.2 on a Sarin and 34.4 on an OGI Megascope. Which is right??? Well machines all have tolerances and such. As such if you change the angles in the HCA just by .2 here or there, you'll see a different score overall.

So it's a nice way to weed out "losers", but don't just buy because there is a low score on HCA.

Good luck!

 

[glt4392]

Stephan,
Here is the stone I gave as an example of the 3.2 score
This stone was at a local dealer:
color: E
clarity: SI1
weight: 1.31
sarin report was:
diameter: 7 (6.97-7.03) 0
total depth: 4.38 62.6%
crown height: 1.12 16% 35.5 degrees 0
pavilion: 3.02 43.1% 40.9 degrees 0
table 3.87 55.3% 0
girdle medium 0
GIA excellent, excellent.
Diamond description said: ...meets requirements for AGSL "ideal" cut diamond, shows heart and arrow pattern.." Now, I did see the hearts and arrows and they looked very sharp and symetrical to me but it was unbranded so I don't know if it was in fact that.
The .9 was scored by a stone that was a 1A cut accross the board except for a 13% crown and a 33 crown angle so it was not an ideal cut.

 

[Stephan]

I understand your problem.
I think I would buy the HCA 0.9, if it has a GIA EX/EX.

 

[glt4392]

but do you see where a consumer like myself now gets comfused, due to the result of this tool, you would sacrifice the "ideal cut" grade for a lower grade cut but higher score. And this is also seen in some of the "ideals" and H&A shown in some sites. Some get 1.x some 2.X and they are I thought as close to 100% light return as you can get. After looking a stone after stone for a long time, I noticed that the regualar consumer only sees a stone at 1x magnification and not with tools. So when does a score from this tool make or break a stone? Is a 1 point difference in score equal to what shine and fire difference...10, 20, 30? Is a 3 x% more than a 2 (high limit for excellent) I am trying to quantify the value of this tool for a consumer like myself. Specially after CUT is being permanently implanted into eveyone's brain here.
After a while I feel that while a lot of the information given here is amazyingly usefull and the pursue of that perfect cut is fine, I have now experienced first hand that put together a cut 0 or 1 is almost impossible to tell appart by a normal person. So as everyone argues that it is impossible to tell between a D and an F color would a normal person know the difference when a 1 is put next to a 3 scored in the HCA? or a two? if they are all ideal and excellent polish and symetry?
Can someone with multiple stones see what honestly their stones look like side to side and what they score?

thanks

 

[Stephan]

Only one solution : ask CutNut on this forum !

He can tell you a lot about the HCA...

So, guys, it's 2AM here and I go sleep now...

C U tomorrow !

 

[Richard Sherwood]

You're talking about nuances.

Take for example body color. You might not notice the difference between an "F" and a "G" color, but you would notice a difference between an "F" and an "H".

Does the "H" look bad? No. The "F" just looks better though.

Same goes for say a "1" and a "2". To the lay person, they might not see a difference, but they would between a "1" and a "3".

There's always a reason why a stone scores lower. Look for example at the following DiamCalc simulated images for the 1.31 carat that ranked a 3.2. It may fall within the technical parameters of an AGS 0, but those are only numbers. What counts is the optical performance of the stone, and some AGS 0's don't perform as well as others. The HCA will help you weed those stones out.

The crown/pavilion angle combination of this stone creates an area of moderate leakage under the table. In the first image (IdealScope), this shows up as the very light pink areas under the table facet. In the second image (PhotoReal), it shows up as a dark area under the table facet.

A person who never looks much at diamonds would say, "Wow! Gorgeous stone", while a PriceScope educated consumer who had trained his eyes what to look for by examining different diamonds would spot that the center of the stone showed some darkness.

 

[Richard Sherwood]

Simulated idealscope image...

 

[Richard Sherwood]

Simulated photoreal image

 

[glt4392]

Thanks, I wish I had that tool you used as well!

 

[Mara]

BTW Stephan--I have seen AGS0 stones that score between 3-5 on the HCA...they are all over the place. Blue Nile has some...DCD has some..I found some on random other sites. Every time I find a stone with an AGS cert and AGS 0 proportions, I plug it into the HCA for curiousity's sake. While the ratio is better than 50/50...there are still alot of AGS 0 stones that come up with non desirable scores on the HCA. Non-desirable to me for a purchase now would be anything over 2.5 (though if I was buying now I'd focus on under 2.0)...but alot of these come up with scores in the 3.5-4.5 range..not exactly 'ideal' on a scale to 10.

IMO use the HCA as one tool of many to make your decision. But just because the stones are AGS 0 does not mean that the stone is excellently cut. IdealScope images may look great to your eyes, but you are not trained to look for the details that mark down the stone. Neither am I...most IdealScope images look darn good to me, as do alot of H&A images that have been rejected as TRUE H&A's because of small details. Just seeing hearts and arrows does not mean that its a true H&A stone.

It's all very tricky...got about another 10 months for research? That is how long it will take to learn many of the nuances...and even then you won't be done!

Good luck!

 

[glt4392]

SO with that said, and I understand how that stone can score just that now. It is so much easier when you SEE IT. Thank you again for the images. Now, does that mean that a stone like Mara's (I hope you don't mind!) from another post with the following dimmensions:
table: 61.4%
depth: 56.9%
crown angle: 29.9% (very shallow...under 30 is always noted on GIA report)
pav angle: 41.1%
culet: none (under 1%)
which she mentioned that scored under a 2 a few months back and now scores a 2.5 and
which is obviously not an ideal cut diamond, will return more light and have more brilliance and fire and therefore give more sparkle to the naked eye (look shinier) than the ideal given as an example here?
Or is the overall "shine" not completely meassured by this tool?

 

[Richard Sherwood]

The beauty of a diamond is a balancing act between five factors:

Brilliance (white light return, positive effect)
Fire (dispersed colored light return- rainbow colors, positive effect)
Contrast (light-dark-light-dark scintillation, positive effect)
Light leakage (negative effect)
Fisheye effect (reflection pattern of girdle seen inside table, negative)

The durability of a diamond is affected by the following factors:

Thinness of the girdle
Shallowness of the crown angles

All these factors need to be taken into account when considering a stone. Take your last stone listed, for example. A simulated IdealScope image of the diamond is attached.

As is immediately obvious, this diamond does indeed have more brilliance (white light return) than the previous 1.31 carat mentioned (see IdealScope tutorial). The dark reds and pinks attest to that.

But what negatives lower the HCA score? (I got 2.8 when I input the numbers). The lower crown height combined with the lower crown angles diminish the fire (colored light return), while the "headlight" brilliance of the stone tends to diminish the light-dark-light-dark contrast scintillation of the stone. The shallowness of the stone gives a great surface diameter, but also makes the girdle reflection inside the table seen easier when the stone is tilted.

Add to this the increased probability of chipping because of the sharper crown angles and a girdle that is probably thinner than the norm, and you understand the lower HCA score.

2.8 versus 3.2 is a close race. You would have to view both stones in order to decide which "look" you like best.

 

[Mara]

My stone is VERY white brilliant, at the price of less fire and scintillation. Definitely. But in certain lighting, my stone is a fireball. So it's kind of like a lighting hunt..I always feel like I get a special treat when I find great lighting, say in a restaurant, because it shows me my stone in an entirely more colorful light that I don't get to see everyday.

Ideals or SuperIdeals or Excellently cut stones 'ideally' have a balance of the white light and fire and scintillation...as opposed to a stone like mine which is heavy on white light and less on fire and scint. It's a preference thing, you have to like a stone that exhibits alot of white light, or else it may just look like a rock to you at times. If you have a FIC, you have to like the color light more heavily than white light..etc etc. Many people that go 'ideal' are happy with the 'balance' of white light, fire and scint that is struck within their stone. A good way to understand this a little better is to look at some of the Bscope images on the GOG site...some are really off the scale on the fire side and lower on the white light side...those probably display more color than white light (by a miniscule amount to naked eye) and vice versa.

The shallow crown angle of my stone does indeed lend itself to the stone chipping more easily. We got insurance and don't worry about it anymore. The girdle is thin-med...so not quite a bad thing..but better safe than sorry.

Lastly, important to note that tools such as HCA assume your stone has excellent symmetry, so if it does not, the results will be different of course. This would be important if you were running a stone through the HCA that has Good symmetry as opposed to an Excellent.

Oh and BTW Rich..no girdle reflection in my stone!!! and definitely no fish-eye!

 

[Garry H (Cut Nut)]

glt you asked about DiamCalc
"Thanks, I wish I had that tool you used as well!"
You can get it from the main page here, and from www.ideal-scope.com for $280.
It is a very powerful proffessional tool and lots of fun too

It is possible for the steepest crown and deepest pavilioned AGS 0 proportioned diamond to score 4.9 on HCA, and yes it is pretty silly to call such a stone "ideal".

AGS will change their grading system. Sooner the better