Question - Light Performance based on cut

[dmus]

I really enjoy this site and want to thank all you regulars for your insight and patience. I''m addicted.

Question:

Does an AGS0 H&A have better light performance than an AGS0 no H&A? Or is it just the characteristics of the light performance are just different? I ask because the H&A doesn''t do much for me if the light performance of a AGS0 non H&A is just as good. Or am I missing the point, namely excellent optical symmetry performance which is a trade mark of H&A gives better light performance.

Need help understanding these nuances. Thanks.

 

[strmrdr]

depends on the lighting most of all then how far off from h&a it is and diamond size.
The answer is yes no maybe so ...

on advantage of h&a is:
Balanced contrast - nice arrows and messy hearts will get the same result.
Nice patterns - nice arrows and messy hearts will get the same result.

All the facets work together:
This is an advantage but how much of one is endlessly debated.

workmanship:
I love workmanship and the fact that I bought a diamond with superior workmanship is a "mind clean" issue for me like D and IF is for others.

The crown, pavilion angles and lgf% all have too work together or h&a is meaningless.

When PSers talk of h&a diamonds they are really pursuing the proportionally correct h&a diamonds with the best polish and symmetry grades possible not just h&a diamonds. Some of which have the best physical tightness of the range in angles that anyone can cut too take it too the next level of diamond insanity.
ie: superieur workmanship.

 

[dmus]

Date: 3/13/2008 7:43:48 PM
Author: strmrdr
depends on the lighting most of all then how far off from h&a it is and diamond size.
The answer is yes no maybe so ...

on advantage of h&a is:
Balanced contrast - nice arrows and messy hearts will get the same result.
Nice patterns - nice arrows and messy hearts will get the same result.

All the facets work together:
This is an advantage but how much of one is endlessly debated.

workmanship:
I love workmanship and the fact that I bought a diamond with superior workmanship is a ''mind clean'' issue for me like D and IF is for others.

The crown, pavilion angles and lgf% all have too work together or h&a is meaningless.

When PSers talk of h&a diamonds they are really pursuing the proportionally correct h&a diamonds with the best polish and symmetry grades possible not just h&a diamonds. Some of which have the best physical tightness of the range in angles that anyone can cut too take it too the next level of diamond insanity.
ie: superieur workmanship.

So you can have H&A but have angles that don''t work together reducing performance. If so an AGS0 H&A doesn''t necessarily have better light performance than a plain old AGS0?

 

[strmrdr]

Date: 3/13/2008 9:07:22 PM
Author: dmus
So you can have H&A but have angles that don''t work together reducing performance. If so an AGS0 H&A doesn''t necessarily have better light performance than a plain old AGS0?

yes h&a without good angles and matching lgf% will have reduced performance but if its ags0 the pavilion and crown angles and lgf% will almost always work together(some combos are better than others).

 

[strmrdr]

keep in mind that ags0 isnt the end all of round diamond performance either.
I have round mixed cut design that can hold its own with the best of the AGS0 rounds in performance and smoke a good many of them that is 99% of the way nailed down, im working to get that 1/10 percent that will make it smoke the best of the best RB.

 

[dmus]

What is a mixed cut design? Is this something different than a 58 facet RB?

Based on what you have said I will tend to look for ideal cuts and forget about having to have H&A because I don''t want to pay a premium if I can get the same light performance with an ideal cut. I do understand I might loose some of the nice consistent patterns H&A may give though.

By the way, I bought a 1.53 AGS000 which is beautiful but never got an idealscope, ASET or H&A pictures to see if it was a H&A because I didn''t know about this stuff before. Now that it''s been set in a ring I regret not having this info because reading here on PS has peeked my interest.

Thanks Strmrdr for your help.

 

[strmrdr]

A mixed cut is one that has a bottom like an RB and a top like an emerald cut or asscher(step cut)

 

[strmrdr]

Date: 3/13/2008 9:44:42 PM
Author: dmus
What is a mixed cut design? Is this something different than a 58 facet RB?

Based on what you have said I will tend to look for ideal cuts and forget about having to have H&A because I don''t want to pay a premium if I can get the same light performance with an ideal cut. I do understand I might loose some of the nice consistent patterns H&A may give though.

By the way, I bought a 1.53 AGS000 which is beautiful but never got an idealscope, ASET or H&A pictures to see if it was a H&A because I didn''t know about this stuff before. Now that it''s been set in a ring I regret not having this info because reading here on PS has peeked my interest.

Thanks Strmrdr for your help.

If your looking for value stones look into some of the JA h&a and non-h&a and the WF ES line, or Wink''s pgs graded stones, Niceice or GOG could round one up too and provide the information needed too select one and skip paying for the report with a cut grade.

 

[dmus]

Interesting. Are there any like that online to look at?

By the way, another thing that bothers me is knowing what are acceptable (good performing ) combinations of P angle, C angle and LGF? I''ve read several threads here but it''s very confusing. I''ve read where you and others have said if the C is like 35.4 or 35 you''d like to see a A angle around 40.6. I''ve also seen comments where certain combinations are called FIC, TIC or BIC. I''ve also seen a generalization where to get a good balance of fire and brilliance you''d like a lgf between 78-82. Is there a matrix anywhere that shows a table of combinations of these and gives a characterization? That would be invaluable for people crazy about these numbers and performance. Something like:

Pav Crown LGF
----- ------- -------

40.9 34.2 76
40.5 35.4 80.2 FIC
41.1 34.5 75 Steep deep, poor light perf

You get the idea. and maybe include what doesn''t go together well. Sorry I got long winded here, but I''m loaded with more questions than answers!

 

[strmrdr]

nope no one is cutting them yet that I know of.

As far as the angles go run it thru the HCA then if the pavilion is in the 40.7-40.9 and the crown around 34.5-35 range then any reasonable lgf is going too work ok.(slight differences in personality)
40.6 can go wither way with needing long or short, 40.5 and under or 41 and over need long lgf% 77%(80GIA) or over. Some extreme combos are best with 85% lgf%.

 

[dmus]

Thanks Strmrdr. Sounds like you weight the importance of the pavillion angle a bit more than the others.

 

[ksinger]

Date: 3/14/2008 2:03:34 AM
Author: strmrdr
nope no one is cutting them yet that I know of.

As far as the angles go run it thru the HCA then if the pavilion is in the 40.7-40.9 and the crown around 34.5-35 range then any reasonable lgf is going too work ok.(slight differences in personality)
40.6 can go wither way with needing long or short, 40.5 and under or 41 and over need long lgf% 77%(80GIA) or over. Some extreme combos are best with 85% lgf%.

I''m reading this thread with interest. Strm, while we''re at this could you possibly give a short low-down on GIA rounding (the thing that made me think of it was you''re comment above). I tried to read through a thread about the new GIA cut system and forced rounding but it assumed a base level of knowledge I didn''t have and quickly became mired in jargon and minutiae that I pretty much couldn''t (actually didn''t want to take the time) to follow. I guess what I''m asking is, I take it there is software involved that forces rounding one way or the other, yes? And that the grader gets to choose the direction of the rounding? So as above, if you really have a lgf of 77%, GIA will almost always round to 80? Are there ever times when rounding is NOT forced? Speak slowly and please frame your response in small minimum syllable words....

I''m SO confused!!!

What else is new....


Mmmmmm!!!!! Sparrrrrkly!!!!

 

[dmus]

Didn''t realize lgf was rounded to 75, 80 or 85?? Does AGS also d this and on the Sarin or Helium or OGi reports if they appear there are they also rounded like this? It dilutes the value of providing the number if so.

 

[Paul-Antwerp]

Storm has informed you correctly about AGS-0 and H&A, but may I add my 2 cents, and give you the scientific background.

AGS grades light performance, based upon a 3D-scan of the stone, and a ray-tracing-program, which tracks where potential rays of light end up. In this regard, they have finished their study on two of the three parts of light return, being brilliance and fire. The scintillation-study is in progress, and is not a part of the light-performance-grade right now. This is not only the case with AGS-grading, most labs are way behind on AGS as far as cut-research is concerned.

The main benefit of H&A is actually in scintillation. Since scintillation is not a part of the AGS-grade yet, it might be interesting to combine the AGS-0-grade with true H&A.

However, like Storm tells you, you also need to be careful, since H&A as such (without checking the AGS-grade) is obtainable in a rather wide range. Many of the stones marketed as H&A would not be considered H&A here on Pricescope.

To summarize it, I think that proportions are the basis, thus the first thing to check is the AGS light performance grade. And within that grade, getting a good H&A-pattern is definitely an extra, especially with regards to scintillation.

Live long,

 

[Ellen]

Date: 3/14/2008 10:04:27 AM
Author: dmus
Didn''t realize lgf was rounded to 75, 80 or 85?? Does AGS also do this and on the Sarin or Helium or OGi reports if they appear there are they also rounded like this? It dilutes the value of providing the number if so.

AGS gives the actual measurement on their grading reports, and the other tests you mention will give actual numbers for any stone.

And yes on diluting, no one is fond of GIA''s rounding.

 

[dmus]

Thanks again for this invaluable info Strmrdr, Paul, Ellen.

Observation:

Based on what Paul has said it sounds like you can get a H&A without being a top grade from AGS or GIA? I''m excluding polish from this statement. Could symmetry and/or proportion be less than 0 on AGS and still get true H&A? If this is generally true it sounds like in order of importance; look for AGS0 for cut for top notch light performance, then look for H&A for the improved light characteristics that Strmrdr and Paul mention. I love the scintillation when my wife moves her hand or when I move my head so now I''m leaning back to wanting H&A as a value add in light performance. Bottom line I''m now thinking for the best light performance you want ideal cut and H&A, not just an AGS0. If this sounds confusing it is. But I definitely have a better appreciation and understanding of H&A value because of your help. Thanks. I''ll probably never b able to afford a diamond again. My standards are quickly sky rocketing out of site!

 

[strmrdr]

A stone that has vg/vg polish/sym could be true h&a and have ags0 light performance but not get the overall ags0 grade.
The lab report symmetry grade is not optical symmetry.

Don''t get too hung up on the AGS cut grade, there are a lot of cutters of exceptional diamonds that only use GIA it is just a little harder too sort them out but some vendors already do that for you.
One of them is on my wifey2b''s finger :}

 

[strmrdr]

Date: 3/14/2008 10:11:54 AM
Author: Paul-Antwerp
Storm has informed you correctly about AGS-0 and H&A, but may I add my 2 cents, and give you the scientific background.

AGS grades light performance, based upon a 3D-scan of the stone, and a ray-tracing-program, which tracks where potential rays of light end up. In this regard, they have finished their study on two of the three parts of light return, being brilliance and fire. The scintillation-study is in progress, and is not a part of the light-performance-grade right now. This is not only the case with AGS-grading, most labs are way behind on AGS as far as cut-research is concerned.

The main benefit of H&A is actually in scintillation. Since scintillation is not a part of the AGS-grade yet, it might be interesting to combine the AGS-0-grade with true H&A.

However, like Storm tells you, you also need to be careful, since H&A as such (without checking the AGS-grade) is obtainable in a rather wide range. Many of the stones marketed as H&A would not be considered H&A here on Pricescope.

To summarize it, I think that proportions are the basis, thus the first thing to check is the AGS light performance grade. And within that grade, getting a good H&A-pattern is definitely an extra, especially with regards to scintillation.

Live long,

yes no maybe so.

I''m not a huge fan of the AGS approach too fire mapping.
Environmental interaction is used too view fire much more often than looking directly at the diamond and that''s not taken into account.

The scintillation study has promise of separating events by size which is good but turning that into a grade is a huge can of worms.
Personal preference plays a huge role and again environmental interaction must be accounted for it too be true too life.

 

[rocku]

Date: 3/14/2008 8:41:04 AM
Author: ksinger
I''m reading this thread with interest. Strm, while we''re at this could you possibly give a short low-down on GIA rounding (the thing that made me think of it was you''re comment above). I tried to read through a thread about the new GIA cut system and forced rounding but it assumed a base level of knowledge I didn''t have and quickly became mired in jargon and minutiae that I pretty much couldn''t (actually didn''t want to take the time) to follow. I guess what I''m asking is, I take it there is software involved that forces rounding one way or the other, yes? And that the grader gets to choose the direction of the rounding? So as above, if you really have a lgf of 77%, GIA will almost always round to 80? Are there ever times when rounding is NOT forced? Speak slowly and please frame your response in small minimum syllable words....

I''m SO confused!!!

What else is new....


Mmmmmm!!!!! Sparrrrrkly!!!!

I read it somewhere that GIA round LGF% to the closest 5%.
So I am assuming 77% would become 75%; 78% become 80%

 

[strmrdr]

Date: 3/14/2008 3:30:36 PM
Author: rocku

I read it somewhere that GIA round LGF% to the closest 5%.
So I am assuming 77% would become 75%; 78% become 80%

77.49 goes down, 77.5 up.

 

[rocku]

Date: 3/14/2008 5:18:48 PM
Author: strmrdr

Date: 3/14/2008 3:30:36 PM
Author: rocku

I read it somewhere that GIA round LGF% to the closest 5%.
So I am assuming 77% would become 75%; 78% become 80%

77.49 goes down, 77.5 up.

Strmrdr, 77.49

that is rocket science.

 

[strmrdr]

Date: 3/15/2008 11:47:48 AM
Author: rocku

Date: 3/14/2008 5:18:48 PM
Author: strmrdr

Date: 3/14/2008 3:30:36 PM
Author: rocku

I read it somewhere that GIA round LGF% to the closest 5%.
So I am assuming 77% would become 75%; 78% become 80%

77.49 goes down, 77.5 up.

Strmrdr, 77.49

that is rocket science.

lol
Of course if you measure it again that might be 77.0 depending on the scanner.
Scanners have a hard time with the lgf% which is the excuse GIA went with for using rounding so the $5k scanners can be used instead of the $20k ones.
In the center of the range other than some slight personality differences it don't matter a lot but once you get out too the edges that 5% can become critical.

 

[diagem]

Date: 3/15/2008 12:02:51 PM
Author: strmrdr

Date: 3/15/2008 11:47:48 AM
Author: rocku

Date: 3/14/2008 5:18:48 PM
Author: strmrdr

Date: 3/14/2008 3:30:36 PM
Author: rocku

I read it somewhere that GIA round LGF% to the closest 5%.
So I am assuming 77% would become 75%; 78% become 80%

77.49 goes down, 77.5 up.

Strmrdr, 77.49

that is rocket science.

lol
Of course if you measure it again that might be 77.0 depending on the scanner.
Scanners have a hard time with the lgf% which is the excuse GIA went with for using rounding so the $5k scanners can be used instead of the $20k ones.
In the center of the range other than some slight personality differences it don''t matter a lot but once you get out too the edges that 5% can become critical.

Storm..., which $20K scanners are accurate...? All the once I tried are a joke with fancy shapes.... (no mater the cost of device...)!

 

[diagem]

Date: 3/13/2008 9:50:19 PM
Author: strmrdr
A mixed cut is one that has a bottom like an RB and a top like an emerald cut or asscher(step cut)

Or vice-a-versa....

 

[strmrdr]

Date: 3/15/2008 12:38:39 PM
Author: DiaGem
Storm..., which $20K scanners are accurate...? All the once I tried are a joke with fancy shapes.... (no mater the cost of device...)!

the 20k sarin does a good job on rounds with all the updates and properly calibrated.
on fancies helium is the only scanner that comes close.

 

[strmrdr]

Date: 3/15/2008 12:54:56 PM
Author: DiaGem

Date: 3/13/2008 9:50:19 PM
Author: strmrdr
A mixed cut is one that has a bottom like an RB and a top like an emerald cut or asscher(step cut)

Or vice-a-versa....

true.
I haven''t tried the reverse yet on diamond models.

 

[diagem]

Date: 3/15/2008 2:55:42 PM
Author: strmrdr

Date: 3/15/2008 12:54:56 PM
Author: DiaGem

Date: 3/13/2008 9:50:19 PM
Author: strmrdr
A mixed cut is one that has a bottom like an RB and a top like an emerald cut or asscher(step cut)

Or vice-a-versa....

true.
I haven''t tried the reverse yet on diamond models.

One thing is for sure..., much more challenging...

 

[strmrdr]

Date: 3/15/2008 3:30:57 PM
Author: DiaGem
One thing is for sure..., much more challenging...

guessing it would take a short first step of 43 degrees on the pavilion then the rest around 41 16 fold.

 

[Garry H (Cut Nut)]

As others have said, just showing great H&A''s does not guarantee good effective proportions.
Here is an example of a stone that shows excellent H&A''s patterns, but it is an absolute woofer

 

[diagem]

Date: 3/15/2008 3:37:00 PM
Author: strmrdr

Date: 3/15/2008 3:30:57 PM
Author: DiaGem
One thing is for sure..., much more challenging...

guessing it would take a short first step of 43 degrees on the pavilion then the rest around 41 16 fold.

Thats the easy way out...

Feeling lazy? Try a 3 or even 4P..., with a brilliant crown it can get pretty interesting!!!

Ooh..., and an 8 fold should be challenging enough...

, but you could always go crazy...