help comparing please?

[gemnewbie]

Can you help me compare the cuts on these two stones. For reading prior posts on here, they both appear to be very similar. Both are round brilliant stones, around the same weight, and have no cutlets or floressence. Assuming no inclusions that would affect light return, would you expect the ASET images to look similar?

I''ve provided the table/depth percentages and crown/pavillion angles for each:

Stone#1-
56%
61.6%
35
40.6

Stone #2-
56%
61.3%
34.5
40.6

 

[stone-cold11]

Maybe, maybe not depends on the alignment of the facets and length of the star and lower half facets too.

Which labs graded these stones? #2 stone might have some obstruction problem if the alignment of the facets and size of the lower half is off.

So best to be able to see the IS/ASET image.

 

[jet2ks]

By the numbers provided, both stones are worthy of further inspection. The numbers you have posted just give an outline, how those lines are filled in will tell the whole story.

ASET/IS images take much more into account than just the numbers you listed, so may or may not be similar. Crown and pavillion angles are the result of the average of the measurements of eight facets each, so you only have some measurements for 16 of the 57 facets. Then with GIA stones, those angles are rounded. How much variation there is in the numbers used to get the averages, which direction the numbers are rounded, the precision of the other "minor" facets, lower half length, and other factors will play into the complete picture of how a stone looks and performs.

 

[outatouch0]

Date: 11/5/2009 5:11:57 PM
Author: jet2ks
By the numbers provided, both stones are worthy of further inspection. The numbers you have posted just give an outline, how those lines are filled in will tell the whole story.


ASET/IS images take much more into account than just the numbers you listed, so may or may not be similar. Crown and pavillion angles are the result of the average of the measurements of eight facets each, so you only have some measurements for 16 of the 57 facets. Then with GIA stones, those angles are rounded. How much variation there is in the numbers used to get the averages, which direction the numbers are rounded, the precision of the other ''minor'' facets, lower half length, and other factors will play into the complete picture of how a stone looks and performs.

wow now THAT was really well said !!! - I can see this statement as a sticky

 

[gemnewbie]

Stone and Jet, thank you very much for the detailed explanation. In answer to your question, both are GIA stones.

So I take it that, even if these four sets of numbers were IDENTICAL, and inclusions were not an issue, two stones with such identical numbers might have significantly different light return?

Sorry to be such an dunce, but could you please explain further, in more lay terms, how facet allignment, lower half length and rounding might affect the ASET/IS images as far as light return is concerned? Any chance that someone might have ASET or IS pictures of a stone with great numbers, but terrible light return based on these factors? Whenever I look at poor light return pictures it appears that the problems are bourne out by the percentages and angles in these numbers.

 

[stone-cold11]

This article on lower half.

http://journal.pricescope.com/Articles/68/1/Do-the-pavilion-mains-drive-light-return-in-the-modern-round-brilliant.aspx

 

[Lorelei]

Date: 11/5/2009 6:41:25 PM
Author: gemnewbie
Stone and Jet, thank you very much for the detailed explanation. In answer to your question, both are GIA stones.

So I take it that, even if these four sets of numbers were IDENTICAL, and inclusions were not an issue, two stones with such identical numbers might have significantly different light return?

Sorry to be such an dunce, but could you please explain further, in more lay terms, how facet allignment, lower half length and rounding might affect the ASET/IS images as far as light return is concerned? Any chance that someone might have ASET or IS pictures of a stone with great numbers, but terrible light return based on these factors? Whenever I look at poor light return pictures it appears that the problems are bourne out by the percentages and angles in these numbers.

Concerning averages, it depends on how tightly cut a diamond is. Imagine a diamond circle and the appropriate angles, the angles can have some variance and ideally you want as little variance as possible between them. If your angle averages start swinging out all over the place, this can affect efficiency of light return leading to light leakage.

With rounding, some borderline angle combos can go one way or another depending on that rounding. For example shallow shallow angle combos ( 40.6) or shallow pavilion combos ( 41>). If the proportions are in fact shallower for the rounding for a steep deep then the diamond might be perfectly fine and not show leakage, if steeper then leakage is a real possibility. Sometimes lower half measurements can help particularly if longer to reduce leakage but not in all cases.

Moral of the story - images are the best method of evaluation.