Find your diamond
Find your jewelry
shape
carat
color
clarity

Directionality of different cuts?

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
7,863
This is a quick post as it came to mind just now but I'm supposed to be writing a job application... :???: lol


I was just wondering - is there a 'best' cut in terms of 'directionality' (or lack of it)?

To put that into English :lol: I am thinking about the angle of tilt at which different cuts 'stop working' and start windowing (for example).

For example, 'classic' ovals seem to often be windowing on the far side in the videos once they near 90 degrees of tilt/rotation (or even much lower angles of rotation) but some asschers seem to work well at all angles in the videos (bar 'side on', obviously).


Is there a trade-off between having an excellent play of light head-on but then a somewhat leaky stone once tilted?

Or can cuts be designed to balance (or even maximise) 'off-axis' performance at the expense of head-on performance?

Is it simply a limitation tied to the pavilion angles and how they will become see-through as they approach being perpendicular to the angle of viewing?


I recall reading a Instagram post from Yoram a while ago, or it might have been his website, where he said that his antique cuts are optimised to work well 'off-axis'.



Anyway, as I say - this is a quick and dirty brain-dump post - any input would be appreciated! :))
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
15,656
I started putting it together in my head but just an explanation of methodology of a comparison would be huge.
Leaving it to Karl and Yoram!!!!
But even within individual shapes proportion variations can result in totally different effects. For example emerald cuts with very dark obstruction issues look great when tilted away fronm the obesrver
 

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
7,863

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,313
To do proofs and ranking is not going to be practical at this time so this is my opinion and is not taking into account some obscrure cuts.

Off Axis looks is not one single factor but many.

1: 3d sculpture look/art/presence. When looking at the side of the stone on the hand the setting and the diamond form a sculpture.
This will range from the diamond standing proud and having a strong 3d look for the high crowned designs to a flat top princess cut with almost no presence other than the setting.
"modern ideal" cut rounds fall in the middle some place.

2: White light return off axis.
High top pears in my experience are very high in this area of performance along with high crown step cuts.
Not to pick on princess cuts but they are really not that great at doing off axis so I will put them at the bottom.
"modern ideal" cuts are again in the middle some place.

3: Fire off axis.
Pretty much the same story with white light but more commonly seen.
High top pears in my experience are very high in this area of performance along with high crown step cuts.
Im going to pick on princess cuts they are really not that great at doing off axis so I will put them at the bottom.
"modern ideal" cuts are again in the middle some place.

An oec with a high crown scores well as sculpter, a little back on off axis white light and fire than the top end but well above the mrb ideal cuts.

Yes, there are worse designs than the princess cut but they are the most common of the lower end of off axis performance.
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,313
The best off axis performance I have ever seen have been high top pears, high crown step cuts, and one I can not name because.
What say you?
 
Last edited:

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,313
part 2 of directionality is how wide an area they draw light from face up?
This is something that if you not careful designing for ags0/ASET will kill this for on axis performance.
This is part of what I rant about the mrbification of diamonds.
Long story, no time :}
 

AV_

Ideal_Rock
Joined
Aug 5, 2018
Messages
3,889
[QUOTE="Garry H (Cut Nut), post: 4777069, member: 1006"
emerald cuts with very dark obstruction issues look great when tilted away fronm the obesrver
[/QUOTE]

Love of my life
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,272
Yoram,
Can you provide details on the cut parameters? Is this a proprietary cushion?
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,313
Talking about tilt in aset looking at it both in virtual and under the scope it does not aline with what I see in person as well as face up does.(not perfect but in the right ligting not bad face up)
Many of the areas aset shows as leaky are actualy fiery and they are brighter than aset indicates.
I admit to a small sample size and not scientifically sound but to me its atleast a trend.
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,272
Just a note about AGSL light performance grading - the ray tracer tests performance through a range of tilt. Performance must hold up through a minimum of 15 degrees in order to achieve a cut grade of ideal.

Looks to me like Yoram's example is holding up well at 20 degrees.
 

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
7,863
Talking about tilt in aset looking at it both in virtual and under the scope it does not aline with what I see in person as well as face up does.(not perfect but in the right ligting not bad face up)
Many of the areas aset shows as leaky are actualy fiery and they are brighter than aset indicates.
I admit to a small sample size and not scientifically sound but to me its atleast a trend.
ASETscope imaging uses a light source from behind and then the ASETscope on top of the diamond, the edge parallel with the girdle, doesn't it?

I guess I'm wondering if you're seeing the results of light entering from the horizontal axis and reflecting off what ASET suggests are leaky facets (which wouldn't come up in ASET as the light sources aren't there in ASET)?
 

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
7,863
The best off axis performance I have ever seen have been high top pears, high crown step cuts, and one I can not name because.
What say you?
The Cut That Shall Not Be Named was sort of a prompt for this thread, actually :D

The central stripe of what appears as small triangles seems to window a bit when tilted past a certain angle, going from Yoram's recent videos, but the rest of the facets each side of that central stripe are still working well :)

I know that not all leakage is bad as it can in some ways also be considered as contrast, and that a stone in motion on the finger is totally different to a studio lighting environment and slow-motion movement, so I didn't think it would be any sort of issue 'in real life', but it made me wonder! :D
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,313
@OoohShiny yep it exists. Nature of the beasts the other side of the crown becomes the efective pavilion bypassing the pavilion at extreme angles..
Since there is a ton of sparkle and fire moving it hides.
Static the 3d statue effect is primary and there is rarely total darkness on the other side of the stone.
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,313
I do not find that all that accurate relative to what you would actualy see but it ahows it exists with all cuts.
 

diagem

Ideal_Rock
Trade
Joined
Oct 21, 2004
Messages
4,960
Yoram,
Can you provide details on the cut parameters? Is this a proprietary cushion?
Hi Bryan, Yes its proprietary so wont get into numbers here but in general its an opposing design to a standard Tolkowsky, very shallow pavilion combining a significant steep/high crown, small table and of course a Kozibe (trade-mark of mine).

And was described by an AGS senior gemologist as a "fire cracker", a term I adopted with pride.

M8F_Izo.png M8F_tilt_HDR.png
 

diagem

Ideal_Rock
Trade
Joined
Oct 21, 2004
Messages
4,960
Just a note about AGSL light performance grading - the ray tracer tests performance through a range of tilt. Performance must hold up through a minimum of 15 degrees in order to achieve a cut grade of ideal.

Looks to me like Yoram's example is holding up well at 20 degrees.
The problem for this design was its face-up position, originally the design consisted of wider (thicker) arrows (four main blues), at Aset 40 it displayed to much obstruction (blue) but it the tilted position it passed 000 with no efforts. We fixed it.

Also because of U/LGF azimuth limitations, one of the sections (C/P) possessed a bit more dugout halves and created an uneven girdle as per AGS standards, this was fixed as well. Below is an AGS explanation to the illustration attached.

"Here is an ASET 33.5, ASET 40, Reverse Fire Map and Forward Fire Map for the scan of m8f-13 for AGSL analysis srn that you emailed me.

The stone gets a 0 for light performance. There is a girdle deduction (very thin) and I noticed on the scan that the symmetry has some problems - pointing and a wavy girdle - so you won't get a Triple 0 report unless you clean it up."

It was all cleaned up and we achieved the Ideal 000 for this design..., and the rest is history as they say.


M8F_AGS_analysis.jpg
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
15,656
Just a note about AGSL light performance grading - the ray tracer tests performance through a range of tilt. Performance must hold up through a minimum of 15 degrees in order to achieve a cut grade of ideal.

Looks to me like Yoram's example is holding up well at 20 degrees.
This is one reason why AGSL fancy shape cut grades do not work.
For rounds there is not a huge difference in angle of rotation of viewing.
Imagine how this would work for other shapes.
For e.g. the style of crushed ice cushions used for fancy yellows when tilted away 45 degree (image tilting to 1.30 on a clock) and you see right out the big window top right.

https://youtu.be/uVqlptC7_WU
https://youtu.be/thhWHnWtjz0
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,272
This is one reason why AGSL fancy shape cut grades do not work.
For rounds there is not a huge difference in angle of rotation of viewing.
Imagine how this would work for other shapes.
For e.g. the style of crushed ice cushions used for fancy yellows when tilted away 45 degree (image tilting to 1.30 on a clock) and you see right out the big window top right.

https://youtu.be/uVqlptC7_WU
https://youtu.be/thhWHnWtjz0
Looks like it works for Yoram's cushion.
 

Texas Leaguer

Ideal_Rock
Trade
Joined
Jul 27, 2009
Messages
3,272
Indeed. The Octonus model looks outstanding and performs well thru tilt.

AGSL does not currently cut grade ALL facet configurations. Only the ones that fall into their already developed algorithms. Certain configurations may require R & D and a taylor made set of metrics. All are possible in their system, but the demand may not be there for some configurations.
 
Be a part of the community It's free, join today!
    20th Anniversary Upgrade
    20th Anniversary Upgrade
    Horses for Courses: Polo Match Jewelry
    Horses for Courses: Polo Match Jewelry
    An Excellent K Color Graded Diamond
    An Excellent K Color Graded Diamond

Need Something Special?

Get a quote from multiple trusted and vetted jewelers.

Holloway Cut Advisor



Diamond Eye Candy

Click to view full-size image.
Top