Crown and Pavilion?

[DND168]

Hi all, I know in order for a diamond to maximize light return, the Crown and Pavilion angles are very important, however on this site there is no mention of what are the ideal angles... I.E like for table and total depth we were given an ideal range, but are there such ranges for the Crown and Pavilion? or are these two measurements contingent on all other measurements of the stone with respect to table, and depth?

 

[oldminer]

Back in the dark ages, about three or four years ago, when we still sort of thought the sun and planets revolved about the earth, we also promoted certain crown and pavilion angles as sacred to the best of diamond cuts. Some of this is still natural law, but some of this has now proven subject to new technology of many kinds.

Diamonds have certain weaknesses. Below a 30 degree crown angle combined with a thin girdle is a somewhat durability compromised stone. Over certain crown and pavilion angles the stone may still look good, but because of too much depth it won''t look proper for its weight. It will look rather too small in diameter. Overly thick girdles also diminish overall size appearance.

You can use angles and percentages for screening purposes. You should not use them for the final decision process on well cut examples. You then should be looking at Beauty, not numbers.

Hope that helps you some.

 

[Regular Guy]

Dave actually is the author of some suggested ranges, still published on this site, and found here.

Another page you may find helpful here, also in the tutorial, is this one.

Regards,

 

[beryl]

. The 'ideal' proportions, 'discovered' by Tolkowsky circa 1910, are pavilion main slope = 40.75°, crown main slope = 34.5°, and table size 54% (Tolkowsky said 53% but made an arithmetic error). His theoretical reasoning is discussed in "'Diamond Design' Revisited", which is published by Octonus at www.gemology.com. Actually he obtained these data by measuring diamonds polled as 'best' by the public and his treatise incorrectly explains 'why'. This was the standard used for grading by GIA for many years. Michael Cowing says that an American cutter, Morse, did it before Tolkowsky but did not write about it.
. Since then, in works by GIA, MSU, Garry Holloway, and myself ("Faceting Limits", 1975, now reprinted at Octonus website), we have learned that other combinations are also attractive but favor brightness or 'fire', from which the buyer can select his/her preference. Much, much, much was discussed about this in 'DiamondTalk' forum circa 2000-2002 and at the IDCC conference in Moscow May, 2004. New grading standards by AGS and GIA address these variations and the proportions of secondary facets as well (note that pavilion 'mains' are no longer dominant; the 'halves', when 80% deep, become the dominant feature of the pavilion and are at about 42°)

 

[Regular Guy]

Date: 9/29/2005 5:36:54 AM
Author: beryl

(note that pavilion 'mains' are no longer dominant; the 'halves', when 80% deep, become the dominant feature of the pavilion and are at about 42°)

Beryl,

I suppose this sort of thing has been discussed here for some time...but...care to elaborate?

For example, from a purely non-technical perspective, I offered this as a question in February, and it appears that you're pointing to a variation in the percentages I posed in the opening of that thread. Relatedly, from the point of view of the consumer, on the ground, what tools do you see as most effective for making informed choices for optimizing light performance in diamonds?

Thanks,

 

[beryl]

Date: 9/29/2005 6:41:54 AM
Author: Regular Guy

Date: 9/29/2005 5:36:54 AM
Author: beryl

(note that pavilion ''mains'' are no longer dominant; the ''halves'', when 80% deep, become the dominant feature of the pavilion and are at about 42°)

Beryl,

I suppose this sort of thing has been discussed here for some time...but...care to elaborate?

For example, from a purely non-technical perspective, I offered this as a question in February, and it appears that you''re pointing to a variation in the percentages I posed in the opening of that thread. Relatedly, from the point of view of the consumer, on the ground, what tools do you see as most effective for making informed choices for optimizing light performance in diamonds?

Thanks,

. The others must be sleeping; I expected to find a myriad of comments and arguments here tonight.
. I am not involved in diamond buying or selling. My contributions are usually technical, for which I have recently been criticized, but I will offer some thoughts - and that''s all they are.
. We know that Tolkowsky proportions are near the center of the ''good design'' spectrum; GIA ansd MSU studies have shown this. Hiowever, when Tolkowsky ''chose'' these proportions the halves were rather short - perhaps 65-75%; the ''mains'' were the dominant factor in the view through the table; now they are not. Studies by MSU and GIA, circa 1999, were with 80% halves (measured the GIA way, 82% measured the MSU way).
. It is my feeling that when the pavilion halves are too long they overpower the effect of the ''mains'' and there is not as strong contrast effect as the stone is moved; furthermore, dynamic contrast is still happening over a wider range of tilt angles. On the other hand, their slopes are closer to those of the mains, so it takes less tilt to cause a change in contrast = mini-scintillation.
. I think that very long halves create more of a ''reflector'' than a ''gem'' - as might be the case if they were 100% and there were no mains.
. My personal preference is lots of dynamic contrast as the stone is waggled over a wide range - rather than brilliance. I hear about stones that blind someone on the other side of a restaurant; I''ll bet that these have very long pavilion halves.
. I can''t back any of this up with experience or scientific data - it is my ''gut'' feeling - some of it seen while cutting colored stones. ... and what is ''beauty'' is the beholder''s preference.