2 questions re: princess cuts & crown/pavilion angles

[nswartzb]

I understand that crown and pavilion angles are interdependant, that it is really best to see a stone in person to judge beauty, optical performance, etc., and that there are always exceptions to any "rule." That said, I have 2 questions:

1. Is there a TYPICAL OR ACCEPTABLE RANGE for crown and pavilion angles for top-of-the-line princesses (an AGA 1A or 1B), say a square (1.0 LxW ratio) stone with something like a 70% depth, 65% table, 10% crown, and 1-5% girdle?

2. What amount of variation among the crown and pavilion angles is TYPICALLY acceptable? For exmaple, the 4 sides a stone with an average crown angle of 37.5 and an average pavilion angle of 60 could have sides of 35, 35, 40, 40 (crown) and 57.5, 57.5, 62.5, 62.5 (pavilion) or it could have sides of 32.5, 32.5, 42.5, 42.5 (crown) and 55, 55, 65, 65 (pavilion). I''d guess the former numbers would be better, but when should variation become a cause for concern?

Thanks in advance for comments.

 

[researcher]

Every stone is different, so it's hard to say. This website by White Flash should help answer your questions though:

Princess Stones

 

[nswartzb]

Again, I just asking about RANGES and what you'd expect to see -- I know these are just guidelines. And can't even the second question be answered? For example, (and I know these dimension probably aren't possible), shouldn't one be concerned is the 4 side angles were 30, 30, 45, 45 (crown avg 37.5) and 50, 50, 70, 70 (pavilion avg 60)?

 

[valeria101]

There is no HCA-like rule to guess brilliance using numbers (angles) about a princess.

But you may find this page (LINK) interesting. It compares two AGA 1A princesses that are only told apart by their angles.

And there is more worth reading where this page comes from.

Also, it may not be very important to look at the average angles, 'cause a princess cut is not supposed to have just one of each, but two of each - so you would have to look at a combination of two pavilion and two crown angles respectively. And no one made up a clear rule just yet.

 

[oldminer]

For the questions you have asked, the answer is that the AGA charts don't use angles for fancy shapes. They can be all over the place and "average" does not really address it. WHat needs to be done is a simpler task. Look at crown height and symmetry. If the crown height of a princess is between 10%-15% and the symmetry is excellent to good, there will be no or nearly no variation in angles or facet arrangment. Then we have the crown issue settled. The same with depth. In a princess with the proper total depth, proper crown height, and with excellent to good symmetry, we will have little or no issue with improper pavilion angles or facet matching.

Looking at angles is for engineers, but is not needed for grading fancies. You can approach it that way if you prefer to do so, but the time involved is greater than the logical shortcut I have laid out above. Since I do this all the time, it seems doubtful to me there is a valid reason to go to the longer method. For engineer types we provide these numbers sometimes but I prefer not to interpret them in a way that means more than doing it my own preferred way.

 

[nswartzb]

Thanks. Your explantion of the relationship btwn symetry and varition in crown/pavilion angles was very clear and useful.

 

[nswartzb]

I have noticed that every (or almost every) SuperbCert Princess cut has a crown angle between 34 and 38 degrees and a pavilion angle between 56 and 60 degrees. The stones generally have a 10% difference between the depth and table -- depth in high 60s/low-mid 70s and table in the high 50s/low-mid 60s.
Barry, do you wish to comment on this? Anyone else?