How does lower girdle length affect face up performance?

[Rhino]

Date: 6/8/2008 6:45:15 PM
Author: Wink
Well, I was going to chime in that I think that when the lower girdles are towards the long end of the Exellent to Ideal range (GIA and AGS) that the flashes get smaller and often the diamond will show less dispersion, ESPECIALLY IN LOW LIGHT.

That is because dispersion''s flashes must be broader than the pupil of the eye at the point at which that light reaches the eye. The longer lower girdle facets create smaller flashes (shorter) flashes to begin with so more of the dispersion events will not be perceived as dispersion, but as white light since when all of the light enters the eye at the same time it is perceived as white by our eyes. Only when the entire flash of dispersion is NOT received completely in the iris of the eye do we perceive those wonderful flashes of color that some of us love so intensely.

Add to the already shorter width of the dispersive flashes in the longer lower girdle facets the widening of the iris in dim light and you begin to understand that if you are a dispersion fan you will probably want diamonds more to the middle or lower range of the lower girdle facet lengths if you wish to see the maximum dispersion in your diamond in lower light situations.

Then I was going to add that this is completely a matter of taste and that provided both stones are well cut that they will both be beautiful, but with slightly different flavors.

Then I saw the epic work provided by John Pollard and I decided not to expose the lack of time and effort that it would take me to respond what I was thinking when he has delved so deeply into the subject. It would just be too embarrassing...

Wink

Greetings Wink,

In the above I''m taking it to mean in low spot type lighting. Correct me if I''m wrong.

Something that I am noting in the diamonds I''ve specifically been having cut is that I am having the pavilion mains cut in the 40.7 - 40.9 neighborhood which is causing the lower halves to fall greater than 41 degrees. This is causing the lower havles (which are now comprising the majority of real estate on the pavilion) to grab lots of light from around the observer resulting in more pinks and slightly less blues in ASET as seen in John''s graphics.

The bold flash you get off of wider pavilion mains are now instead diverted to the lower halves. You still get bold flash but they''re coming from the halves now instead of the mains with some nice pin flash too!

So even in diamonds with the longer lgf''s you''ll still get some broad flash action in spot lighting.

In diffuse lighting your contrast pattern changes but again you get lots of great white light return off of those halves taking up more real estate on the pavilion. They''re all honies though.

I recently acquired a 34.5/41.0 combo with 65% lower halves in what I''d consider an "Ideal" proportioned OEC. Perhaps one of the best I''ve purchased through estate and wow is it pretty too!

 

[Rhino]

Date: 6/8/2008 6:41:01 PM
Author: John Pollard

Date: 6/8/2008 6:33:19 PM
Author: agc

John, just noticed something on your reflector images. Starting at 80 there is a dark area forming at the bases of the arrows and it gets more pronounced as lgf increases. What is this?

Oldminer was right...you are hungry. You realize the silent PS choppers and guys in black neoprene suits may come and get you tonight.

It''s how we recruit.

You''re seeing table reflection; the reflection of the table seen in the pavilion of the diamond. It is more obvious in diffuse lighting than in direct or filtered.

More info and graphics on table reflection: https://www.pricescope.com/community/threads/cut-question-for-non-aca-diamond.86196/

Just to add to John''s comments. While you do see table reflection on the pavilion the specific phenomena you are talking about agc isn''t entirely dependant upon the table as much as it is lower girdle facet length. Especially when talking about diamonds with ideal parameters.

My research has shown me that when you lengthen the lower half facets you cause more reflections off the pavilion to exit straight up through the table in that controlled environment as blacks in red reflector images are reflections of the eye/camera of the observer. The larger the diamond the easier it is to see the visible effects of doing this in the cutting. I would also add and emphasize that those darker reflections you see at the arrows shafts are then further amplified through the star facets. If you look carefully at any red reflector image (or ASET or DiamCalc image in controlled lighting) and you see those dark reflections at the arrows shafts take note of the blacks you see exiting the stars. The more pronounced they are at the arrow shafts, the more pronounced they will be in the stars. There will generally always be that corellation. This is one reason in larger diamonds I really like longer lower girdles coupled with good star length.

This, IMPO is what contributes to the higher pin flash observed in diamonds of this type as compared to say the 73-75% length.

When you get to diamonds less than 1ct though its not as easy to observe the effects of this.

Hope that helps.

Kind regards,

 

[honey22]

At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

 

[arjunajane]

Honey, I will let the experts answer the more technical parts of your question

But as I have recently just researched this myself, my understanding is a longer or shorter lgf will just create a different "flavour" of H&A stone (of course assuming C and P angles work together etc).
Neither is any better or worse, just a personal preference.

I think Jon has some videos if he cares to share..

 

[Lorelei]

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let's say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

I think the difference can be seen if you know what to look for, my diamond has long LGFs and this is apparent in some lights. As to whether we should be considering LGFs when advising, we need to be aware of the potential to overcomplicate things for some posters, so I think if the poster mentions they want to know more about LGFs, then that is our cue, but not everyone wants or needs that level of info, so personally I think it is best for us to play it by ear so to speak!

 

[honey22]

Date: 6/9/2008 4:57:07 AM
Author: Lorelei

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

I think the difference can be seen if you know what to look for, my diamond has long LGFs and this is apparent in some lights. As to whether we should be considering LGFs when advising, we need to be aware of the potential to overcomplicate things for some posters, so I think if the poster mentions they want to know more about LGFs, then that is our cue, but not everyone wants or needs that level of info, so personally I think it is best for us to play it by ear so to speak!

I can always count on you for a good answer Lorelei! Thanks! I quite often suggest stones and didn''t want to be leading someone up the garden path with such an important purchase!!

 

[Lorelei]

Date: 6/9/2008 6:06:25 AM
Author: honey22

Date: 6/9/2008 4:57:07 AM
Author: Lorelei

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

I think the difference can be seen if you know what to look for, my diamond has long LGFs and this is apparent in some lights. As to whether we should be considering LGFs when advising, we need to be aware of the potential to overcomplicate things for some posters, so I think if the poster mentions they want to know more about LGFs, then that is our cue, but not everyone wants or needs that level of info, so personally I think it is best for us to play it by ear so to speak!

I can always count on you for a good answer Lorelei! Thanks! I quite often suggest stones and didn''t want to be leading someone up the garden path with such an important purchase!!

You are too kind!

I think in the three years I have been here, the level of info has increased tremendously, as has the type of information the newbies request, so it is an excellent question Honey, and one that needs consideration - that we are serving those who seek advice in the best way. You are doing a great job, and I think that is the best way is to know as you do, that one set of advice doesn''t fit all, so I think we are doing the best thing in tailoring the advice we give according to the individual.

 

[Ellen]

Date: 6/9/2008 4:57:07 AM
Author: Lorelei

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

I think the difference can be seen if you know what to look for, my diamond has long LGFs and this is apparent in some lights. As to whether we should be considering LGFs when advising, we need to be aware of the potential to overcomplicate things for some posters, so I think if the poster mentions they want to know more about LGFs, then that is our cue, but not everyone wants or needs that level of info, so personally I think it is best for us to play it by ear so to speak!

I agree, well said miss. I will only bring them up if I see some that are way to one extreme or the other. That doesn''t happen very often.

 

[Lorelei]

Date: 6/9/2008 7:02:25 AM
Author: Ellen

Date: 6/9/2008 4:57:07 AM
Author: Lorelei

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

I think the difference can be seen if you know what to look for, my diamond has long LGFs and this is apparent in some lights. As to whether we should be considering LGFs when advising, we need to be aware of the potential to overcomplicate things for some posters, so I think if the poster mentions they want to know more about LGFs, then that is our cue, but not everyone wants or needs that level of info, so personally I think it is best for us to play it by ear so to speak!

I agree, well said miss. I will only bring them up if I see some that are way to one extreme or the other. That doesn''t happen very often.

Fankies!!

 

[Garry H (Cut Nut)]

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

It is semantics and taste Honey, except that the longer lgf stones should not be called classic H&A''s.

John and Jon are each making assessments of how these diamonds perform in different lighting types.

I ran DCPro for various table sizes for a huge variety of factors including various fire metrics, and it would seem that fire will take a hit once you pass above 80% lgf length (82% lgf Depth). But we are only talking 2 or 3%.

 

[Rhino]

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let''s say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

Insofar as "that much better" ... I leave that for the consumer to decide as it is their eyes that must be pleased at the end of the day. On a personal note I like each the same. When I''m showing clients diamonds and I have both alternatives available I''ll show them to the best of my ability what those differences look like and let them decide. I''ve done this with more than one PS''r and some who have even flown to our store after seeing the comparison via the web to ensure that their eyes weren''t playing tricks on them. Bem for example was one who preferred the longer LGF''s among others who do also. I don''t and wouldn''t tout longer LGF''s as superior to shorter LGF''s although and vice versa. As expressed its a matter of preference and that between 2 equally beautiful diamonds, all other things being equal. Insofar as "true" Hearts & Arrows go, one is not superior to the other ... closed clefts or open clefts. 76-77% lower havles or 80-83%. Again it is a matter of preference. One is not superior to the other.

All the best,

 

[Rhino]

Date: 6/9/2008 8:26:44 AM
Author: Garry H (Cut Nut)

Date: 6/9/2008 2:22:52 AM
Author: honey22
At the risk of sounding like a dope here

Is the average person (or even the educated PSer let's say) going to be able to tell the difference when looking at a stone with shorted lgf compared to longer lgf assuming that table, crown and pav numbers are the same? Is one going to look that much better that you would easily chose that stone?

I am curious as when I purchased my stone I obsessed over the numbers - crown, pav, table and depth until I nearly went insane. I ended up with an ACA so all my fears were put to rest. However, I never even considered lgf. Is it something we need to look more closely at when picking a stone, or for example, can I simply chose an ACA or AGS 000 stone and know that it will be top-notch without even considering lgf?

It is semantics and taste Honey, except that the longer lgf stones should not be called classic H&A's.

John and Jon are each making assessments of how these diamonds perform in different lighting types.

I ran DCPro for various table sizes for a huge variety of factors including various fire metrics, and it would seem that fire will take a hit once you pass above 80% lgf length (82% lgf Depth). But we are only talking 2 or 3%.

There are other optical technologies that suggest fire and sparkle are increased once you hit the longer zone too. It's minutia and I'd agree though ... not an insanely notable difference. I see it more easily in the larger sizes. Hope things are well in Oz there.

 

[Rhino]

Date: 6/9/2008 2:46:10 AM
Author: arjunajane
Honey, I will let the experts answer the more technical parts of your question

But as I have recently just researched this myself, my understanding is a longer or shorter lgf will just create a different ''flavour'' of H&A stone (of course assuming C and P angles work together etc).
Neither is any better or worse, just a personal preference.

I think Jon has some videos if he cares to share..

As much as I like to contribute educationally to a subject here on PS, as a vendor I am prevented from linking to my site. Too bad we can''t embed.