Hit me if you can!

[Rhino]

Hey Al,




I wouldn't say there is a hugely perceptible difference either. As stated earlier, in the critical analysis I've found the slightly steeper combo to outdo the slightly shallower combo in some circumstance. Generally though the shallower combo generates better optics most of the time. Again... this is not any kind of huge difference either way especially when you consider the amount of crap on the market that these are compared to.




Peace,


Rhino

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On 1/20/2004 3:08:33 PM aljdewey wrote:







Actually, I'm not sure that's entirely the heart of the issue, PQ.




What I understand Stephan to be noting is that the angles are often at the upper end of the range on BOTH angles, and he's asking about how that affects the performance.




The crown/pav angles are almost like a yin-yang.....for each move up in one angle, there should be a corresponding move down in the other angle to preserve 'optimal' performance.




So, if the 'superideal' range on crown is 34.3 to 34.8, and the range on pavilion angle is 40.6 to 40.9....Stephan is observing that many of the stones reflect angles on the upper end of BOTH ranges, instead of upper/lower. So,


he's saying '34.3 would be most optimally suited for 40.9, yet most of these stones are closer to the 34.8 than the 34.3.'




I guess my comment would be this. If the ranges were bigger, I'd expect it to have a much more direct impact on performance. When you're talking about SUCH a narrow window of ranges, I'm not sure I think there'd be a hugely perceptible difference.

----------------

 

[Paul-Antwerp]

Stephan,

First of all, I have to thank you for plugging our product. I feel ambarassed to say, that in the meantime, I have extreme difficulties to find the perfect rough stone for you. I hope that you can hold on for somewhat longer. In the end, you will get exactly what you want.

Now, may I add some technical notes, and maybe tear open the discussion. Let us assume that we, being cutters of super-ideals, all aim for that sweet spot-combo where the M.S.U.-studies show that you have the highest quality of light return.

What most of you do not know, is how diamonds are cut, and more specifically how one facet is cut. Cutting does not happen in a linear movement, but in a circular movement. In the last four years, I have designed about a dozen tools, which allow cutting in a linear movement, but none of my cutters wants to work with it, because it is too difficult for them or because it slows them down.

For those who cannot follow anymore. With linear movement, I mean the following: when starting the cutting of a specific facet, you start at 40.7° and you stay at that same angle, until the facet is finished. In reality, you have a circular movement: you start a facet at 42, then you make the circular movement to 41.5, then to 41 to try and stop exactly at 40.7°. Now let this sink in, and then try to follow the rest of my explanation.

Suppose that you are aiming for 40.7, but you stop cutting at a certain point in time, because you think that you are there. You take the stone out of its tool, and check it on the Sarin or the OGI. This machine shows you that you have stopped at 40.9°. Now, you can put the stone back into your tool (very difficult to put it in the exact same way) and you can recut each facet for a few seconds in order to come to 40.7°. That is extremely difficult, and I can fully understand that a lot of cutters would not risk it and leave the stone at 40.9°.

The same is true for the crown, only there it is even more difficult to obtain a specific angle. In the pavillion, your cutting tool gives you some idea of where you are going, but in the crown, you can only judge by eye.

Knowing this, I think that it is natural that most cutters maintain a slightly deeper pavilion and a slightly steeper crown.

We, from our side, try to go for that sweet spot at whatever risk. However, this also creates the problems which you can see in the stone that pqcollectibles brought up. In that case, we went slightly too far in cutting the pavilion, ending up with 40.4°. Too bad, impossible to correct.

I hope that I have shed some light on the difficulty of cutting to this extreme detail. We tend to take more risk in obtaining the best possible combination. Sometimes, I wonder if that extra risk is worth it.

Maybe, you guys can give your opinion whether that extra risk is worthwile.

Looking forward to your opinion,

Paul

 

[Mara]

I was actually talking to Brian at WF last nite regarding this same thing Paul...he called to discuss my wedding ring and we got off on a tangent about crown and pav angles. He noted the exact same thing you did. That you can cut to try to reach a certain angle, but that the precision can be so hard to attain that many times you are so close...but can't really risk trying to get any closer because of the fear of over-shooting the mark, as you note with the 40.4 stone, and then having something that possibly would not meet your brand requirements.




In reality as others noted, the beauty of a stone is not really quantifiable by angles or numbers...but rather to the naked eye. I would venture to agree with F&I in that a well-cut stone will most likely be darned beautiful. If enough care is put into cutting...then chances are very good you will have a beautiful stone.

Everyone's 'sweet spot' may be different.

 

[valeria101]

Paul, did anyone do some senzitivity analysis on these issues? Talking about a tenth of a degree sounds rather extreme to me. If there is a sweet spot in sizing these angles, I really doubt that it is a unidimensional "dot" - there must be a level of tollerance for these angles given what can be seen and appreciated in the end result. If color and clarity grades that fall just under the limit of visibility make sense for preserving the credibility of the grading system, could some similar policy be applied to cut quality? Did anyone try? Just curious, as usual...

 

[Garry H (Cut Nut)]

Thanks for the lesson Paul, it was well stated and made sense to me.

What would you think about cutting the crown angle first and where ever it falls, the pavilion be cut to the sweet spot for that stone.

In many instances there is more weight to be gained in the crown anyway.

 

[mdx]

This\thread is certainly becoming interesting.

The bottom line point I was trying to demonstrate with that actual example is that I know there are a lot of excellent skillfull cutters out there (and I am sure Paul is one) that have the willingness and skill to produce beautiful diamonds but are often limited by available material.

These cutters often have to contend with expensive rough with odd shapes coupled with the practical mechanical problems Paul mentioned., but still use the available research to create technical works of art maybe outside the popular “sweet zones” but still conforming to the generic term “Ideal”

It’s for this reason I am reluctant to criticise a diamond on only one dimension but prefer to look at it as a whole. The example I showed might have had some weird looking numbers but the internal geometry was not that different to the popular “Ideal Cuts” The two examples that Gary (Cut Nut) posted demonstrates that there is a lot more to it than popular numbers.

Gary - cutting the crown first? that could be interesting. What do you think Paul

Johan

 

[pqcollectibles]

Thank You, Paul, for your interesting view into the world of cutting! As always, your post was filled with information. As for the risks you take, in cutting rough, I don't see a problem for the consumer. The stone I pointed out was an example of the "non sweet spot" looking like a good performer on paper. I doubt you would have put your logo on the girdle if the diamond were a dud. I will be interested to see the response to Garry's question about cutting the crown first.

Lots of people have bought diamonds that looked great on paper and no one complains. Mara noted the numbers kinda relieve some of the worries associated with buying site unseen. And so far, many people have been more than pleased. Rhino noted a specific combination that he finds more appealing, but he sees waaaay more diamonds than most of us. Most of us only care if our diamond sparkles and shines, draws our eye, and knocks our socks off. Not many diamonds I've seen other people wearing do that. But, my ACA's most certainly do. I am constantly getting compliments from people on my A Cut Above diamonds.

F&I is right. There are the diamonds you see in person that grab your soul. Are the numbers right?? Who cares!! You love the personality that exudes from that fiesty little hunk of carbon!!

 

[Stephan]

----------------
On 1/20/2004 3:08:33 PM aljdewey wrote:


a) So, if the 'superideal' range on crown is 34.3 to 34.8, and the range on pavilion angle is 40.6 to 40.9....Stephan is observing that many of the stones reflect angles on the upper end of BOTH ranges, instead of upper/lower. So, he's saying '34.3 would be most optimally suited for 40.9, yet most of these stones are closer to the 34.8 than the 34.3.'


b) I guess my comment would be this. If the ranges were bigger, I'd expect it to have a much more direct impact on performance. When you're talking about SUCH a narrow window of ranges, I'm not sure I think there'd be a hugely perceptible difference.
----------------

Hello!

Sorry for my late reply, but with the Vietnamese New Year, it's hard to find an open internet cafe!

Thanks Paul for your explanation!

My reply:

a) 34.8, 40.9 ???
Hum... That's not the sweet spot of David Atlas... Look at the charts!
Do you guy's really think that a distortion of the arrow-pattern is important for the life in your diamond? I think that if that what you need is an excellent symmetry: all the arrows have to be the same. The fiery diamond of Johan does certainly have particular arrows with such a shallow pavilion, but I believe that his diamond must be breath-taking...

b) I can see a huge difference between two of my diamonds:

1) 0.8 I-VS1 GIA certed EX/EX, 60.6 depth, 56% table, 34.3 crown, 40.9 pavilion, H&A.
2) 0.64 N-VVS2 HRD certed VG/VG (finish grade and proportions), 59.5 depth, 58% table, 14% crown (+/- 33.7 degrees), 43% pavilion (+/- 40.7 degrees).
Both diamond are not fluorescent and have pointed culets.

Everybody on this forum will take the first stone, if I offer to choose one. Why? It's bigger, better color, AND you think : "that's the sweet spot!".
The first one seems to be shallow.

The difference between this 2 diamonds is VERY perceptible, believe me!

If I take the 2 diamonds and stay far from the mirror (+/- 4 meters), you only see the 2nd one twinkle. It's scintillation is spectacular and it has some huge flashes of color. It looks BIGGER and has more LIFE. At +/- 30cm, you will also notice more fire on the second one. That's why I believe in the HCA cut adviser, who penalizes the GIA certed stone with "only" very good spread and scintillation. The HRD stone has 0.8 TIC with 4 EX! And as we all know, the cut adviser takes consideration of the MSU-charts. And we should all know that the most "super-ideal brands" on the market are slightly to deep.

 

[Stephan]

Oh, and I forgot: of course I will wait, Paul!
But I hope that the Euro will stay high !!!