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is a stone with a pavil angle of > 41'' that bad? i know the HCA ...

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Dancing Fire

Dancing Fire

Super_Ideal_Rock
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Apr 3, 2004
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kills the stone with a pavil angle of 41'' or more but, i have seen couple of stones that is" lively" so could the HCA be wrong about > 41 pavil ?

1- 34.5 crown combine with 41.2 pavil

2- 34.9 crown combine with 41.1 pavil
 
AGS have changed their new system.

They agree with me now that those proportions are AGS2 to 4
 
From what I can gather Brian tends to disagree.
From what i understand of his thinking on the matter with the proper crown angles and the right minor facet cutting they can be every bit as good as 40.9 and lower out to a max of 41.2.
Without actual seeing them I cant say if I agree or not but I put a lot of weight in his opinion.
Im pointing this post out to John to verify that I understand what Brian was saying currectly.
 
Date: 3/20/2005 10:44:40 PM
Author:Dancing Fire
kills the stone with a pavil angle of 41'' or more but, i have seen couple of stones that is'' lively'' so could the HCA be wrong about > 41 pavil ?
Click to expand...
The HCA was not meant to handle everything, no ?

It was good to sort through the old AGS0 for the unfortunate few in the upper right corner of that box. Now there''s new AGS0... so there need for a new box with the proverbial (*) missing corner !
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(*) this reffers to a Romanian proverb... hard to translate. I am all ears for an appropriate English fit, Garry
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my two cents..i have earrings that have about a 41 pav angle if i remember correctly, ACA stones. they sparkle like mad. but my H SI1 large stone and this new J SI stone both have a 40.8 pav angle and they both seemed more eye popping than my earrings.

it sounds odd that such a small difference could really be noticed, but i think when you compare a stone side by side then maybe you can see small nuances..don''t know if you can attribute that entirely to the pav angle...but i definitely prefer the lower pav angle when it is possible. for earrings though, i personally don''t mind that 41 angle as they aren''t as visible as something worn on the hand.
 
Date: 3/21/2005 1
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1:36 AM
Author: strmrdr
From what I can gather Brian tends to disagree.
From what i understand of his thinking on the matter with the proper crown angles and the right minor facet cutting they can be every bit as good as 40.9 and lower out to a max of 41.2.
Without actual seeing them I cant say if I agree or not but I put a lot of weight in his opinion.
Im pointing this post out to John to verify that I understand what Brian was saying currectly.
Click to expand...
strmrdr

i notice WF aca stones are cut closer to teh 41'' pavil....now on the other hand,Paul of infinity diamonds cuts pavil more closer to 40.7'', so alot of his stones will score under 1 on the hca ,because of the more shallow pavil.
 
Date: 3/21/2005 2:24:35 AM
Author: Mara
my two cents..i have earrings that have about a 41 pav angle if i remember correctly, ACA stones. they sparkle like mad. but my H SI1 large stone and this new J SI stone both have a 40.8 pav angle and they both seemed more eye popping than my earrings.

it sounds odd that such a small difference could really be noticed, but i think when you compare a stone side by side then maybe you can see small nuances..don''t know if you can attribute that entirely to the pav angle...but i definitely prefer the lower pav angle when it is possible. for earrings though, i personally don''t mind that 41 angle as they aren''t as visible as something worn on the hand.
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mara
could it be the size of the stones?. well....i saw a stone today .72 ct, crown 34.5'' X 41.2'' pavil that sparkle like mad.
 
They will look great loose in tweezers or in open backed mounts.

Seet them and get a little dirt on the back and see who is right
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Date: 3/21/2005 4:40:25 AM
Author: Garry H (Cut Nut)
They will look great loose in tweezers or in open backed mounts.

Seet them and get a little dirt on the back and see who is right
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Garry
i''ll make sure i have dirty hands the next time.
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I suppose one thing about your incredible questioning of any thing and evrything I say or suggest Storm is it makes me think of simple answers.

LeakageISbadSmall.jpg
 
yeah but no but yeah but no but yeah but the question* wasnt about a C of 35° but 34.5° and 34.4°

ooo Is that a new super volcano found erupting in Oz... or Just Garry melting in frustraition?






























*Need to have seen Little Britain to understand that one...
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Date: 3/21/2005 6:21:39 AM
Author: Garry H (Cut Nut)
I suppose one thing about your incredible questioning of any thing and everything I say or suggest Storm is it makes me think of simple answers.
Click to expand...

Garry thats how I learn :}
There are a lot of areas where one person says one thing and one another so I try to get more information to see where both sides are coming from.
It just so happens that a lot of times your stuff is different than im hearing from others.
Thank you for having the patients to answer the questions and clarify your position.
 
Date: 3/21/2005 2:30:55 AM
Author: Dancing Fire
Date: 3/21/2005 1
6.gif
1:36 AM

Author: strmrdr

From what I can gather Brian tends to disagree.

From what i understand of his thinking on the matter with the proper crown angles and the right minor facet cutting they can be every bit as good as 40.9 and lower out to a max of 41.2.

Without actual seeing them I cant say if I agree or not but I put a lot of weight in his opinion.

Im pointing this post out to John to verify that I understand what Brian was saying correctly.
Click to expand...
strmrdr


i notice WF aca stones are cut closer to teh 41'' pavil....now on the other hand,Paul of infinity diamonds cuts pavil more closer to 40.7'', so alot of his stones will score under 1 on the hca ,because of the more shallow pavil.
Click to expand...

The diamonds have different personalities.
Paul''s are know for an incredible amount of smaller flashes of light that add up to a whole lot of return.
The aca''s return broader flashes of light but fewer of them but they too add up to a whole lot of light return.
The 8* returns fewer yet flashes but they are bigger yet.

Which is better?
Depends on what you like and the lighting.

I recommend a study of the diamond pictures on the b-scope images on goodoldgold.com for seeing the different personalities of the different cutting styles.
 
Date: 3/21/2005 9:24:50 AM
Author: strmrdr

The diamonds have different personalities.

Paul''s are know for an incredible amount of smaller flashes of light that add up to a whole lot of return.

The aca''s return broader flashes of light but fewer of them but they too add up to a whole lot of light return.

The 8* returns fewer yet flashes but they are bigger yet.


Which is better?

Depends on what you like and the lighting.


I recommend a study of the diamond pictures on the b-scope images on goodoldgold.com for seeing the different personalities of the different cutting styles.
Click to expand...

But is that difference more down to the length of the lower girdles that give those charatoristics you mention...

75% LGs give fatter arrows = broader flashes - 80% = less broad and 85% = thin arrows... thin flashes..
 
Date: 3/21/2005 2:13:14 PM
Author: Lord Summerisle
Date: 3/21/2005 9:24:50 AM

Author: strmrdr


The diamonds have different personalities.


Paul's are know for an incredible amount of smaller flashes of light that add up to a whole lot of return.


The aca's return broader flashes of light but fewer of them but they too add up to a whole lot of light return.


The 8* returns fewer yet flashes but they are bigger yet.



Which is better?


Depends on what you like and the lighting.



I recommend a study of the diamond pictures on the b-scope images on goodoldgold.com for seeing the different personalities of the different cutting styles.
Click to expand...


But is that difference more down to the length of the lower girdles that give those charatoristics you mention...


75% LGs give fatter arrows = broader flashes - 80% = less broad and 85% = thin arrows... thin flashes..
Click to expand...
Ah someone has been paying attention.
Iv just got a few minutes and this is a complicated issue.
The minor facet cutting has to match the major angles for it to perform well.
A long lgf combined with a 35/41 stone gives you the steep/deeps that Jon talks about not performing well.
Shorten them up a tad like the ACA and you get the performance back up.
All the facets have to work togehter and all of the cutters of super-ideals have different ideas about what the best combination is.
There are some combo's that fight each other and result in less performance.

Take Paul's recipe if they were cut 34.1/40.9 leaving the minors the same they would have different personalities and different performance.
They would still likely have smaller flashes then some but not the massive amount of fine flashes they have now.
 
Date: 3/20/2005 11
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6:49 PM
Author: Garry H (Cut Nut)
AGS have changed their new system.

They agree with me now that those proportions are AGS2 to 4
Click to expand...
Garry
so when the new ags cut grade comes out any stone with a > 41'' pavil will not make teh "0" cut?
 
Storm,

I must say, you are an incredible observer.

The main point is this, I think: in our cutting, we approach an area, where the labs (AGS and GIA) say that there is a ''whole lot of shaking going on'' (thank you, Jerry Lee Lewis).

For AGS, we are very close to an area, where cut-grading suddenly goes from grade-0 to grade-3, with just a slight difference.
For GIA, if we deviate just slightly from our goal-angles, we suddenly end up in their second grade, in stead of the top-GIA-grade.

In this, we follow the studies and the theory of Bruce Harding, who claims that, for all gemstones, the known best area of performance is very close to an area, which one should avoid at all cost. We always describe it in this way: ''the most beautiful flowers grow at the edge of a cliff''.

In our cutting, we aim to get as close to that cliff as possible. This results in the obserations that you describe.

Live long,
 
There is an important distinction to be pointed out here. We have observed that Diamonds .35cts and down can have up to 41.1 pav because we seem them perform better. Brian’s favorite parameters are pavilion 40.6 to 40.9. Occasionally he will brand one >.35cts with a 41.1, but the rest of the proportions – including minors – must fall into specific parameters (as Strm has discussed). 41.2 is a NO NO.

Paul - Strm is an excellent listener & observer and has a very analytic mind. We burn the yahoo oil often.
 
Date: 3/21/2005 2:56:24 PM
Author: Paul-Antwerp

In this, we follow the studies and the theory of Bruce Harding, who claims that, for all gemstones, the known best area of performance is very close to an area, which one should avoid at all cost. We always describe it in this way: ''the most beautiful flowers grow at the edge of a cliff''.
Click to expand...
Great way to put it!
 
Well, there it is: A set of ray tracings showing the changes in path as pavilion anglegoes over the cliff!

I've been curious to see just that sort of thing for a few months. Thanks very much for doing that, Garry!

Okay, so what does it mean?

It seems to show that at 41.1 there is a broadly refracted path being returned upward, called out as 45%

Then at, moving downward in pavilion angle, it jumps to 57%, then settles in at 60%, 63%, 62%.

How closely does that number equate to light return? It's not that P40.7 is returning one-third more light to the eye, is it?
 
Let''s see if this works....

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It is only inside the ''ring of death'' that suffers the No Go Zone very bad leakage.

Humans can see this in stones over about 1/4 to 1/3rd of a carat. Some computerized devices miss it.

It was from making charts like this that I devised hCA.

If you really want to understand this stuff then www.diamond-cut.com.au has been free to read for several years.

Leakage41.5to40.6Small.jpg
 
Hey that is Cool Lost Dog :)

If I was smart I could actually make that movie using DiamCalc
 
And attached is a 57% T 35C 40.7P

IS_AGS-5507909.jpg
 
The back light is a bit strong on DiamCalc, and a bit weak on the photo
 
but those differences... in Dimcalc allow for ease of analysing.. while the darker helps saturate the photo... ?
 
Date: 3/21/2005 2:56:24 PM
Author: Paul-Antwerp
Storm,


I must say, you are an incredible observer.
Click to expand...
Thanks Paul that is a huge compliment coming from you :}
 
I made a DiamCalc movie of the ray trace thingy - if anyone wants it (2MB compressed) email me
garryh at ideal-scope.com
 
Gary, your chart illustrates exactly why I prefer pav angles of 40.6(7) or lower when the crown angles hit 35 or higher.

DF ... if you summarize the info on this thread it is only in smaller goods (under .5xct) where you''ll find good combo''s including 41-41.1 combined with crown angles around 35. In larger goods I generally avoid these and stand in 100% agreement with Gary.
 
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