Confusion about Table, Crown and Pavillion Angles

[lesco]

Reading the recent thread regarding ideal vs. superideal cuts I decided to research prior PS posts. I came across these old tread discussing round''s ideal crown and pavilion angles and I was hoping someone can answer this question.

1- Let''s say you have a diamond with a crown angle of 34, then how do you determine what would be an ideal counterpart in terms of pavilion angles? Is there a chart or something that would tell you, let''s say, if you have a crown angle of 34, the pavilion angle should be within ____ and _____?

2- What does table size tell you? I read on prior posts that ideal table %s range from 52.4% to 57.5%. Assuming this is correct, what''s a better choice: a larger % or a smaller %?

3- Can a diamond be cut too deep or too shallow an still score nicely (under 2) per the HCA? How is it so? I am confused as how all these elements play together.

Thank you before hand for your answers. I hope I get answers to this one. My prior post was not too hot I see.

Leslie

 

[strmrdr]

34 crown 54-57 table? easy 40.9,41 41.1 41,2 pavilion with 80% lgf% and 50% too 65% stars no painting.
How did I know that .. experience and testing combined with virtual diamonds and tools.

2: best pavilion angle for any given table depends on crown angle but the best in the 60% range are in the shallow crown angles/ steep pavilion where 55-57 can work with a wider range of crown angles. The best with tables under 55 is often steeper crowns with shallower pavilions.
The lgf% has too be matched too the c/p combo also.

3: the hca tells you if the crown and pavilion angles work together. Too tell anything else other tools are needed.
The hca reflects its creators bias which is against some steeper deeper combos and for some shallow shallow combos, most of the rest of the world disagrees with him in one area or another at some time or another, which is why some combos may be included under 2 that others think are not soo hot and some may get over 2 that some think are fine.
There are no absolutes!

 

[lesco]

Date: 3/23/2008 7:37:42 PM
Author: strmrdr
34 crown 54-57 table? easy 40.9,41 41.1 41,2 pavilion with 80% lgf% and 50% too 65% stars no painting.
How did I know that .. experience and testing combined with virtual diamonds and tools.

2: best pavilion angle for any given table depends on crown angle but the best in the 60% range are in the shallow crown angles/ steep pavilion where 55-57 can work with a wider range of crown angles. The best with tables under 55 is often steeper crowns with shallower pavilions.
The lgf% has too be matched too the c/p combo also.

3: the hca tells you if the crown and pavilion angles work together. Too tell anything else other tools are needed.
The hca reflects its creators bias which is against some steeper deeper combos and for some shallow shallow combos, most of the rest of the world disagrees with him in one area or another at some time or another, which is why some combos may be included under 2 that others think are not soo hot and some may get over 2 that some think are fine.
There are no absolutes!

Wow... (I guess this is like trying to explain calculus to a first grader) I''m trying to understand #1 and #2 above. So, if you have the following:
Table 57%
Crown angle 34%
Pavilion Angle 41%
You will need an LGF of 80 and a star of about 50% to 65% to make it work right? Anyhow, is GIA thinking about these things when they grade cut?

 

[strmrdr]

Date: 3/23/2008 8:24:04 PM
Author: lesco
Wow... (I guess this is like trying to explain calculus to a first grader) I''m trying to understand #1 and #2 above. So, if you have the following:
Table 57%
Crown angle 34%
Pavilion Angle 41%
You will need an LGF of 80 and a star of about 50% to 65% to make it work right? Anyhow, is GIA thinking about these things when they grade cut?

yep pretty much if you use the gia 5% rounding on the lgf% then its right on. using exact numbers 78%+
AGS takes this into account in a fine grained manner where GIA takes it with a much broader brush due too the rounding they use.
That does explain some of the differences in the 2 grading systems.
The AGS system can take the difference into account of lgf% of 72.6 and 77% which is a large difference optics wise, GIA cant because they round both too 75.
The difference between 77.5 and 82.49 which GIA rounds too 80 is much less a difference opticaly compared too GIA rounded 75(72.5 too 77.49%) with a lot of combos.
In the mid range 40.6-40.9 pavilion with 34.5-34.8 crown there is much less of a optical difference between GIA 75% and GIA 80% lgf%.(72.5-82.49).

 

[strmrdr]

The kewl thing is that you don''t have too know all the fine details of this stuff too find a beautiful diamond.
Using IS and ASET scopes eliminates a lot of it and your eyes can do the rest.

 

[lesco]

Date: 3/23/2008 9:06:37 PM
Author: strmrdr
The kewl thing is that you don''t have too know all the fine details of this stuff too find a beautiful diamond.
Using IS and ASET scopes eliminates a lot of it and your eyes can do the rest.

Thank you strmrdr. I guess you''re right ! The more I read the more I wonder.
By the way, a million thanks. I ended up buying the diamond you gave me the green light on. I am just waiting now for the finish product and yes, I am still thinking about it. I seriously worry about GIA rounding on this stone cause to me it''s borderline in some parameters. This is the link to my prior post.

https://www.pricescope.com/community/threads/help-i-need-opinions-about-this-diamond-please.80808/

 

[strmrdr]

that combo is fine anywhere within the range of the gia rounding, I took it into account and thought about what it would look like on the extremes of the rounding and its fine.

 

[lesco]

Great news ... (relief)

 

[lisa1.01fvs1]

Date: 3/23/2008 8:59:15 PM
Author: strmrdr

Date: 3/23/2008 8:24:04 PM
Author: lesco
Wow... (I guess this is like trying to explain calculus to a first grader) I''m trying to understand #1 and #2 above. So, if you have the following:
Table 57%
Crown angle 34%
Pavilion Angle 41%
You will need an LGF of 80 and a star of about 50% to 65% to make it work right? Anyhow, is GIA thinking about these things when they grade cut?

yep pretty much if you use the gia 5% rounding on the lgf% then its right on. using exact numbers 78%+
AGS takes this into account in a fine grained manner where GIA takes it with a much broader brush due too the rounding they use.
That does explain some of the differences in the 2 grading systems.
The AGS system can take the difference into account of lgf% of 72.6 and 77% which is a large difference optics wise, GIA cant because they round both too 75.
The difference between 77.5 and 82.49 which GIA rounds too 80 is much less a difference opticaly compared too GIA rounded 75(72.5 too 77.49%) with a lot of combos.
In the mid range 40.6-40.9 pavilion with 34.5-34.8 crown there is much less of a optical difference between GIA 75% and GIA 80% lgf%.(72.5-82.49).

Strmrdr:

Just covering my thread questions.

What about P/40.9 and C/35.2 w/ lgf% 75? Any significant optical change here?

 

[strmrdr]

Date: 3/24/2008 1:42:49 AM
Author: lisa1.01fvs1
Strmrdr:

Just covering my thread questions.

What about P/40.9 and C/35.2 w/ lgf% 75? Any significant optical change here?

some, Id want it on the longer side of the GIA 75% range.
ie: 76-77.4
That is one you have too have a full sarin or an IS image on too tell for sure whats goin on the gia numbers dont tell the full story.

 

[lisa1.01fvs1]

Date: 3/24/2008 2:29:01 AM
Author: strmrdr

Date: 3/24/2008 1:42:49 AM
Author: lisa1.01fvs1
Strmrdr:

Just covering my thread questions.

What about P/40.9 and C/35.2 w/ lgf% 75? Any significant optical change here?

some, Id want it on the longer side of the GIA 75% range.
ie: 76-77.4
That is one you have too have a full sarin or an IS image on too tell for sure whats goin on the gia numbers dont tell the full story.

Thanks for the speedy reply actually not GIA but Tifffany''s.

just curious where to get a sarin?

 

[strmrdr]

Date: 3/24/2008 2:36:07 AM
Author: lisa1.01fvs1


Thanks for the speedy reply actually not GIA but Tifffany''s.

just curious where to get a sarin?

some appraisers have them and it can be pretty accuratly guessed at from an IS image.
A sarin scan cant be used mounted, a IS image is the better option than unmounting it.
I have no clue if tiff rounds or not.
In an open setting a string or stick and a marker can be used also too get close.

 

[strmrdr]

also what is the table size? that can change things slighly also but not as much as the c/p combo.

 

[lisa1.01fvs1]

Date: 3/24/2008 3:44:24 AM
Author: strmrdr
also what is the table size? that can change things slighly also but not as much as the c/p combo.

Strmrdr you''re a doll or insomniac or diamond dali lama (sp).

The table is 57%, c/35.2, p/40.9, lgf%/75

ttldepth/61.9, crwnht/15.4, starlgth/55, pavdepth/43.3, gird/med-slthk