Ideal proportions.

[lenhejo]

Hi everyone.

Can anyone fill me in on what exactly ideal proportion means? I used to think that meant H&A, but thanks to all of you I know now they are two different things. When they say ideal proportions, are they referring to the table being between 58%-60% (not sure if these numbers are accurate) and depth perception being between xx and xx. If so, doesn''t the GIA certification rate these characteristics of the diamond.

Thanks

 

[oldminer]

American Ideal Cut
Table %53.0%-58.0%
Crown Angle 34.0°-34.7°
Crown Height %14.3%-16.3%
Pavilion Depth %42.8%-43.2%
Girdle Thickness:Thin to Medium or Medium to Slightly thick
Total Depth %58.70%-62.30%
Polish / Symmetry Excellent-Very Good
The above is a synopsis of the AGA Cut CLass 1A parameters for "Ideal Cut " rounds. This is the traditional approach and there are new ideas about light behavior that are creating the possibility that we will have other styles that also some may see as "Ideal".

I doubt anyone will ever have doubts about the Tolkowsky model being anything but Ideal.

The AGA grades are somewhat tighter than the AGS 0 grade which the majority of the trade consier Ideal... Many are okay and I feel some are not quite up to par. Then again, no one came to me for my blessing. While I have a pretty well developed opinion, the AGS is considered very important in what constitutes the wider range of "Ideal" cut rounds.

 

[verticalhorizon]

A-ha! Caughtcha... what about pavillion angle?

 

[oldminer]

With a small to pointed culet, the pavilion percentage depth defines the pavilion angle. It is simple trig. However, I recognize others insist on the angle. If someone prefers to use pavilion angle then they can delete their concern over pavilion depth.

The reason I used depth and not angle is that fancy shapes have no defined place to measure the angle while their depth is a constant against their width. Since we don't use pavilion angle for fancy shapes, I figure it is somewhat a waste to use it for rounds. Depth suffices.

I used crown height and crown angle in rounds, but only crown height for fancy shapes for the same reasons. Since everyone wanted both the angles and the heights for rounds, and they both mean the same thing, I figured, "why not?"
With fancy shapes, the crown height against width has meaning, but the crown angle has little useful meaning as it can vary widely.

Maybe someday all the angles will have importance in some complex formula for best cut. Right now, it is not the case.

 

[verticalhorizon]

I didn't mean to give you a hard time! I'm just being a little devil!

 

[oldminer]

Little devils, no problem. I sort of appreciate someone questioning answers. It makes me try to be complete and fair. Keeps me honest.

 

[Magnum]

Here are the AGS0 proportions in diagram form that oldminer mentioned:

 

[Dancing Fire]

----------------
On 5/24/2004 11:02:28 AM oldminer wrote:

American Ideal Cut
Table %53.0%-58.0%
Crown Angle 34.0°-34.7°
Crown Height %14.3%-16.3%
Pavilion Depth %42.8%-43.2%
Girdle Thickness:Thin to Medium or Medium to Slightly thick
Total Depth %58.70%-62.30%
Polish / Symmetry Excellent-Very Good
The above is a synopsis of the AGA Cut CLass 1A parameters for 'Ideal Cut ' rounds. This is the traditional approach and there are new ideas about light behavior that are creating the possibility that we will have other styles that also some may see as 'Ideal'.

I doubt anyone will ever have doubts about the Tolkowsky model being anything but Ideal.

The AGA grades are somewhat tighter than the AGS 0 grade which the majority of the trade consier Ideal... Many are okay and I feel some are not quite up to par. Then again, no one came to me for my blessing. While I have a pretty well developed opinion, the AGS is considered very important in what constitutes the wider range of 'Ideal' cut rounds.----------------

Hi Dave,

About two weeks ago I sent in a stone to Chris for an appraisal and he did an excellent job explaining to me in detail. The first off of AGA-CERT (SARIN ?)and the second one is off of OGI, there is big differences in proportions between the two reports.

Dimensions: 9.69 x 9.66 x 5.91 (big difference between the 2)

Total depth: 61.1%
Table: 55.7%
Crown height: 15.2%
Crown angle: 34.6%
PAV depth: 43.2%
PAV angle: 41 degrees

Now this second one is off of OGI machine.

Diameter: 9.71 mm (9.70-9.73)
Total depth: 60.8%
Crown angle: 34.2%
Crown height: 14.8%
PAV angle: 40.9%
PAV depth: 43.1%
Table size: 56.3%

My question is: which one would be more accurate? Based on your 1A American ideal cut, what would be the range of the PAV angle?

Thanks,

 

[oldminer]

What you are seeing is the nearly same readings given by the Sarin and Ogi. How different they are is the range of error built into them. It is instructiuve to realize that neither of these devices is highly accurate in the true scientific sense. Much more accurate devices are coming, but not here today.

Picking apart the Sarin or Ogi results without know which one is correct or if either is partially or totally correct, would be a foolish excerise. We have no standard stone to calibrate these beyond diameter measurements. They do have some slight errors built in and they do measure in different ways. CLose is just about right at this point in time.

 

[69gm]

yes, i have heard this too. there is no "perfect". close enough will have to do.

any idea when "better" machines will hit the market and find it's way into your lab, dave?

 

[oldminer]

I expect to have something operational early Fall 2004 in one of my labs.