Tolkowsky Ideal and shallow CA

[whatmeworry]

Long time lurker on PS. Was reading the advanced tutorial on cut and I decided to do follow the math on Tolkowsky''s thesis on the ideal cut and Jesper Paulsen''s addition to the ideal cut when adding a girdle. With a thin girdle, the Tolkowsky ideal would be pavilion angle 40.75 and crown angle around 33.5 degrees, table 55 and depth 61 or so. From lurking on this board, some folks would label crown angles of 33.5 as "shallow". When you add a medium girdle, the Tolkowsky/Paulsen crown angle is close to 33 degrees.

These proportions get great HCA scores yet it is rare to find stones in the virtual databases with these proportions (particularly for crown angles in the low to mid 33s). Is there something wrong with crown angles in the low to mid 33s? Most crown angles in the database stones seem to be in the 34s or higher. What would these "shallow" stones look like? All the ideal cuts I have seen have crown angles in the 34+ range so I can''t comment on seeing such a stone in person. Is there a reason most cutters prefer crown angles above 34 degrees? Is this a consumer preference?

 

[Garry H (Cut Nut)]

Read the stuff that comes up on the link after you do an HCA caalculation.

I prefer them - they do not show dirt and look great from 10 inches away to the other side of the room.

One day the rest of the world will agree.

 

[Dancing Fire]

Date: 5/24/2006 4:48:05 AM
Author: Garry H (Cut Nut)
Read the stuff that comes up on the link after you do an HCA caalculation.

I prefer them - they do not show dirt and look great from 10 inches away to the other side of the room.

One day the rest of the world will agree.

Garry
how shallow is too shallow?

 

[oldminer]

The tradition of cutters aspiring to cut "ideal cut rounds" is to make 34.5 crown angles, not 33.5. Maybe they are wrong to do it that way, but tradition is a very strong force in this field. The details of how to cut diamonds, until very recently, have been left to tradition. Now a wave of technology is rolling in, but it has yet to influence the entire cutting industry quite yet.

Undoubtedly, the traditional world of the diamond cutter is changing. Exactly how fast this will become apparent when you search for specifically cut diamonds is still not known. In time, we will see changes to traditional cuts becoming more accepted and available.

 

[whatmeworry]

Dave,
Interesting about tradition and the cutting industry. Jesper Paulson points out that Tolkowsky made a rounding error in his thesis. Had Tolkowsky corrected that error, the crown angle in his thesis would be 35 degrees not the 34.5 target of today''s industry! Do you know if the 34.5 target is worldwide or is just geared to the U.S. market?

Thanks,
WMW