LGF and Stars

[Daniel B]

I understand that lengthening the LGF''s to 80-82 will open up the stars and give a diamond more Scintillation and fire.

On the other hand, wouldn''t 65% stars give more pop and fire than 55%. So why would some people prefer 55%, in essence reducing the fire and scintillation? Storm- I think of you here.
Also, what is the best combo for LGF''s and Star% and why? In other words, which combo give the MOST fire and Scintillation?
Thanks!

 

[JohnQuixote]

Date: 12/2/2005 1:04:50 AM
Author:Daniel B

I understand that lengthening the LGF's to 80-82 will open up the stars and give a diamond more Scintillation and fire.

On the other hand, wouldn't 65% stars give more pop and fire than 55%. So why would some people prefer 55%, in essence reducing the fire and scintillation? Storm- I think of you here.
Also, what is the best combo for LGF's and Star% and why? In other words, which combo give the MOST fire and Scintillation?
Thanks!

This is not an absolute statement Daniel, nor does reducing star length sacrifice performance qualities. As a matter of fact, when the upper girdles are 'taken' (run on the wheel) from the star to the girdle the stars are reduced, but there is not so much angle variance between main crown and upper girdles then - and many people have a preference for the resultant broadfire flashes and fluid quality to the scintillation. More info here if you are interested.

Beyond broad performance the balance of fine (subtle) qualities such as these in a diamond is dependent on overall configuration, and the desirability of configuration depends on the taste of the observer.

The 'best combo' is also about taste. There are different looks. In my opinion, patterning (good optical symmetry) is a must to maximize performance qualities. After that, you will need to observe many diamonds of different configurations in many different lighting conditions to arrive at your preference. There are tremendous fans of short LGF, medium LGF and longer LGF alike when debating the subtleties - and far more fans of 'diamonds' in general who just want overall performance - which is available in all of those combinations.

If there was just one combination of proportions 'at the top,' a lot of us would have nothing to discuss, because all fine-make diamonds would be targeted there.

You have surely absorbed a lot of info in a short time. Until you have seen many well-cut diamonds in these configurations I would resist trying to judge 'best' of such subtle differences. You need to see many, many samples in diferent panoramas of illumination to do that. Don't let anyone else tell you what 'best' is when making tiny distinctions like this. Only your own eyes can tell you that.

 

[Daniel B]

Date: 12/2/2005 1:23:08 AM
Author: JohnQuixote

This is not an absolute statement Daniel, nor does reducing star length sacrifice performance qualities. As a matter of fact, when the upper girdles are 'taken' (run on the wheel) from the star to the girdle the stars are reduced, but there is not so much angle variance between main crown and upper girdles then - and many people have a preference for the resultant broadfire flashes and fluid quality to the scintillation. More info here if you are interested.

Beyond broad performance the balance of fine (subtle) qualities such as these in a diamond is dependent on overall configuration, and the desirability of configuration depends on the taste of the observer.

The 'best combo' is also about taste. There are different looks. In my opinion, patterning (good optical symmetry) is a must to maximize performance qualities. After that, you will need to observe many diamonds of different configurations in many different lighting conditions to arrive at your preference. There are tremendous fans of short LGF, medium LGF and longer LGF alike when debating the subtleties - and far more fans of 'diamonds' in general who just want overall performance - which is available in all of those combinations.

If there was just one combination of proportions 'at the top,' a lot of us would have nothing to discuss, because all fine-make diamonds would be targeted there.

You have surely absorbed a lot of info in a short time. Until you have seen many well-cut diamonds in these configurations I would resist trying to judge 'best' of such subtle differences. You need to see many, many samples in diferent panoramas of illumination to do that. Don't let anyone else tell you what 'best' is when making tiny distinctions like this. Only your own eyes can tell you that.

Yea, I wish i could see tons of diamonds to judge them all by eye, but thats just impossible for me to do so without working in the profession, so thats why Im asking so I can get a least a general picture

i understand table,crown/pav. angles but I want to learn deeper into LGF's/ Stars, UGF, and everything else that can impact a diamond. I read the GOG tutorial on Minor facets and Its really interesting to me.
~Are there such combos that are just more brilliant and scintillating than others? (I'll never know unless I ask an expert). I know I like the mid to longer LGF presense in diamonds as opposed to the fatter arrows. Could anyone tell me what the result would be with, say, 52%, 55%, and 65% stars with a default of 81 LGF? Or tell me what the personality of the diamond would be like with those three combos? I understand this is hard question, but anything would be helpful! Thanks!

 

[JohnQuixote]

Date: 12/2/2005 2:03:33 AM
Author: Daniel B

Yea, I wish i could see tons of diamonds to judge them all by eye, but thats just impossible for me to do so without working in the profession, so thats why Im asking so I can get a least a general picture

i understand table,crown/pav. angles but I want to learn deeper into LGF's/ Stars, UGF, and everything else that can impact a diamond. I read the GOG tutorial on Minor facets and Its really interesting to me.
~Are there such combos that are just more brilliant and scintillating than others? (I'll never know unless I ask an expert). I know I like the mid to longer LGF presense in diamonds as opposed to the fatter arrows. Could anyone tell me what the result would be with, say, 52%, 55%, and 65% stars with a default of 81 LGF? Or tell me what the personality of the diamond would be like with those three combos? I understand this is hard question, but anything would be helpful! Thanks!

Understood, and it's great to have people here who are so interested in details. I relate!

I was fortunate enough to have the opportunity to compare a healthy number of extremely well cut diamonds in short, mid and long LGF configurations very early on in my initiation. Since that time I've seen thousands, and have developed certain preferences and tastes now.

Having said that, I'll tell you that the differences you're talking about become more exaggerated on paper (or the computer screen) than in real life. For instance, in two well-patterned diamonds of similar configurations with the only differences being star lengths as described above, it would be much easier for most people to pick the 65% diamond out by trying to examine its physical proportions than to pick out any difference in performance qualities - and that's hard on a 6.5mm object with the naked eye.

As for brilliance and scintillation, those are quality terms. Given three well-patterned diamonds with logical configurations you can have equal beauty in short, mid and long lower girdles. People have observed that the longer lower girdled diamonds return light more intensely in bright conditions, the short lower girdles return more robustly in soft light conditions and the mid lower girdles are a balance. However (am I saying this enough?),

don't think that these differences are something someone will stop and notice at the bus stop. It's unlikely you will hear - "Word dawg, I'm seeing me some phatty mains on your bling, yo? I'm saying your chromatic flares are kickin', ya feel me?"

Having seen your posts, if your preference is high performance in loud lighting consider those >80% LGF that have been described to you. Make sure the diamond is very well cut the rest of the way too... Average diamonds are often cut with longer LGF because jewelry store lighting makes them look good, but a lot of them leak and don't perform well out of the spotlights. Diamonds with great cut/patterning and longer LGFs can hold their own away from loud lighting.

 

[Paul-Antwerp]

The whole issue about LGF and star size is a detail, that should be looked at after checking out all the other measurements and in combination with the other measurements.

As an analogy, remember the sports-model cars of the 70''s, which were equipped with a new item, spoilers, in order to increase the downward pressure on the car. Some of these spoilers (especially in Europe) were quite impressive, and gave the car a very agressive look.

We, as youngsters, considered a car cool if it had spoilers. Until we noticed that a lot of weirdos just added them on their saloon-car, in order to give them a sporty look. The result there was not extra performance, but just a look. The same is true with the LGF and the star size in round diamonds. It means nothing if the other measurements are not outstanding.

Live long,

 

[strmrdr]

Date: 12/2/2005 6:07:07 AM
Author: Paul-Antwerp
The whole issue about LGF and star size is a detail, that should be looked at after checking out all the other measurements and in combination with the other measurements.

Thats something iv been trying to get accross for a while.
All the facets are related and interact with each other.
Its not about any one or 2 or 8 or 16 facets but how they work together.
just saying it has 65% stars tells you nothing of its performance.
Saying it has 75% lgf% gives you an idea of the personality and very little of the performace but doesnt tell you if its a good diamond.

 

[strmrdr]

Date: 12/2/2005 1:04:50 AM
Author:Daniel B


I understand that lengthening the LGF's to 80-82 will open up the stars and give a diamond more Scintillation and fire.

not true, you can have 40% stars, 50% stars 55%, 60% or 65% all with 80-82 lgf%, the stars are on the crown and lgf on the pavillion they arent related other than fine tuning the performance and personality of the diamond.


On the other hand, wouldn't 65% stars give more pop and fire than 55%. So why would some people prefer 55%, in essence reducing the fire and scintillation? Storm- I think of you here.

opening the stars tends to increase white light return all other things equel

Also, what is the best combo for LGF's and Star% and why? In other words, which combo give the MOST fire and Scintillation?

define most, A short lgf will tend to have broad flashes of fire, long lgf will tend to have smaller flashes of fire but both can have the same total amount

Thanks!

When you get to this level it is very very complicated.

 

[strmrdr]

Sir John I think you badly underestimate how much and when people can see differences in diamonds with just a little education.

I may see more because my brain is tuned to patterns, some people see color some people see patterns.
I cant be the only one out there :}

Yesterday the lady who was programming the stim machine for my elbow had a diamond pendant on:
My observation:
about 6mm or .75-.80 ct
large table 65%
flat crown
so-so symmetry - bit jumbled arrow shafts but they were visible.
girdle was cut for contrast.
i2 clarity - carbon spot visible.
narrow ring of death

The pavilion was fairly deep mosty likely.
color was j or better likely.

overall it was not very bright but had some life too it.

The closest I got to this diamond was around 2.5 feet.

edit: lgf% was on the long side 78%+

 

[Daniel B]

Date: 12/2/2005 7:51:50 AM
Author: strmrdr

Date: 12/2/2005 6:07:07 AM
Author: Paul-Antwerp
The whole issue about LGF and star size is a detail, that should be looked at after checking out all the other measurements and in combination with the other measurements.

Thats something iv been trying to get accross for a while.
All the facets are related and interact with each other.
Its not about any one or 2 or 8 or 16 facets but how they work together.
just saying it has 65% stars tells you nothing of its performance.
Saying it has 75% lgf% gives you an idea of the personality and very little of the performace but doesnt tell you if its a good diamond.

Is there anywhere on the web we can learn how they interact and work together? Ive heard "how they all work together" so often, and i understand it would require a long post, so if someone provide a link, that would be awesome! The GOG tutorial (minor facets) gives some info on it, but is that pretty much all I need to know? I want to know the personality of smallish stars and short lgf/long lgf''s, and vica versa and everything in between. Forgive my cut nut geekiness

 

[Rhino]

Hi Dan,

Just for clarification, on stones with top grade or near top grade optical symmetry, the optics emitted through the stars has a direct correlation to lower girdle facet length. So in that sense the star facets are dependant upon that other measurement. Ie. If you have a diamond with 81% lower girdles adjusting the stars from 55 to 60 to 65 isn''t going to make a tremendous impact on the appearance. Slight if best. I''d show you the optical effects here but I do not have the capability of loading the graphics here that we''ve been using in email together as it exceeds PS file size. If you''d like to see that comparison let me know.

Peace,
Jon

 

[JohnQuixote]

Date: 12/2/2005 8:38:01 AM
Author: strmrdr
Sir John I think you badly underestimate how much and when people can see differences in diamonds with just a little education.

I may see more because my brain is tuned to patterns, some people see color some people see patterns.
I cant be the only one out there :}

Yesterday the lady who was programming the stim machine for my elbow had a diamond pendant on:
My observation:
about 6mm or .75-.80 ct
large table 65%
flat crown
so-so symmetry - bit jumbled arrow shafts but they were visible.
girdle was cut for contrast.
i2 clarity - carbon spot visible.
narrow ring of death

The pavilion was fairly deep mosty likely.
color was j or better likely.

overall it was not very bright but had some life too it.

The closest I got to this diamond was around 2.5 feet.

edit: lgf% was on the long side 78%+

Strm, I hear what you’re saying. I think you misunderstood my point.

My ‘differences become exaggerated in writing’ refrain is because, on a forum peopled by owners of expensive and beautiful diamonds, there have been times a conversation has become exaggerated to the point that it creates fear among casual readers.

Speculation like ‘X LGF will give a diamond more Scintillation and fire, or X reduces fire and scintillation’ results in PMs and emails to me and other vendors with concerns about X +/- 1 (remember 40.6 PAs?).

I seek to reassure people that – while there are educated differences – these are not things a pedestrian will necessarily pick up at the bus stop. Maybe it depends on who is at the bus stop. If it’s Garry he’ll show you his well-cut/not well-cut examples right there... Perhaps bus stop education is flourishing

Actually Strm, your example is good for my point: You’re in a town with no fine-make dealers. Differences in poor, average and very good diamonds can be obvious because the configurations are so broad. A 65% table is like a helicopter landing pad.

Here are DC images of 3 diamonds at completely different quality levels. I think distinctions between these are obvious, even when scant mm across, in both static and dynamic terms (one is my version of the landing pad diamond you described above).

1. Static: You can see difs in face up appearance and symmetry easily between all three.
2. Dynamic: You can see difs in overall performance easily.
3. Environment: Two will be poor to average in low light. The other will easily outperform them.
4. Quality Descriptors: No need to discuss.

 

[JohnQuixote]

Now let’s move into the high-performance zone.

Here are DC images of well-patterned diamonds at proven configurations. Distinctions between them will be much harder to make.

1. Static: An astute observer might pick out differences (star %), even when only mm across.
2. Dynamic: In broad terms of overall performance they will be at equal levels.
3. Environment: In broad terms of overall performance they will be at equal levels.
4. Quality Descriptors: Very slight differences may exist with the third diamond with mvt, particularly for those who have been educated or coached, but it does not require any sacrifice of overall quality or performance (anyone want to guess what observable dif might be?).

I hope that is more clear, Strm.

 

[Regular Guy]

Date: 12/2/2005 4:26:43 AM
Author: JohnQuixote
It''s unlikely you will hear - ''Word dawg, I''m seeing me some phatty mains on your bling, yo? I''m saying your chromatic flares are kickin'', ya feel me?''

OK, sorry to interrupt, I have nothing to add here except for great appreciation for your use of language, John. If you and my computer science editor construction worker West Coast friend Frank Ruggirello were to meet one day I think it would be pure joy for you both.

Please excuse this interruption. Back to work you go.

Regards,

 

[Daniel B]

I about fell over when i read that too!

 

[JohnQuixote]

Date: 12/2/2005 5:47:25 PM
Author: Regular Guy

OK, sorry to interrupt, I have nothing to add here except for great appreciation for your use of language, John. If you and my computer science editor construction worker West Coast friend Frank Ruggirello were to meet one day I think it would be pure joy for you both.

Well Ira, maybe I was just being ''frank.''

 

[strmrdr]

What the guy at the bus stop thinks has nothing important to do with the quality or looks of the diamond.
What matters is how it looks to the person buying it and wearing it.
The bottom line is that there is a difference in some case very subtle like a few percentage star difference to being fairly large like 75% lgf% to 80% lgf%.
These subtle differences can mean the difference between a diamond speaking to a person and it not doing so.

If we consumers want to talk about these differences we are going too.
If it doesnt fit with what some vendors want to push then tough.

Now back to picking diamonds apart for fun and learning :}

 

[strmrdr]

stars:
When you change the star % every facet except the table on the crown changes size and shape and in the case of the upper girdle facets their angle changes as well.
This is shown here.

 

[strmrdr]

Changing the lgf% changes the size of the pavilion facets, the size of the lower girdle facets and the angle of the lower girdle facets.
This is seen here:

 

[strmrdr]

If you remember the lessons from diamond cut 101 you will recall that the relationship between the angles is what drives diamond performace.
In both the cases the crown and pavilion angles are the same but the angles and the size of the rest of the facets changled on the end of the diamond in question.

 

[strmrdr]

For those that need a refresher on which facets are which I borrowed a image from this gog page:
http://www.goodoldgold.com/minor_facets.htm

sorry I didnt include it first.

 

[strmrdr]

75 vs 85 lgf%
even at this small size you can see the difference.
The difference in the real diamonds would be larger because the generated images and photos are static and flattened.

Remembering that the arrow size is inversly related to the lgf%
(arrows get bigger with smaller lgf%)
which is the 75% lgf diamond?

 

[belle]

that''s no small size. you''ve got the equivalent of at least a 5ct stone there. we can still use your example but i think the size needs to be more realistic. also keep in mind that more often than not, the arrows will be silvery white not all dark.

 

[belle]

Date: 12/3/2005 7:59:52 AM
Author: strmrdr
What the guy at the bus stop thinks has nothing important to do with the quality or looks of the diamond.

i don't think that was the point. the point was, once you get to a certain level of performance it is going to be very very hard for ANYONE (including the guy at the bus stop) to discern these differences in a casual environment.

Date: 12/3/2005 7:59:52 AM
Author: strmrdr
What matters is how it looks to the person buying it and wearing it.
The bottom line is that there is a difference in some case very subtle like a few percentage star difference to being fairly large like 75% lgf% to 80% lgf%.
These subtle differences can mean the difference between a diamond speaking to a person and it not doing so.

true but this level of performance these differences are going to be subtle, as you said, and most people coming here are not going to have the luxury of lining up several top cuts to compare their own personal preferences. to try and split hairs in top cuts and push forth an even further limited set of parameters based on ones own preferences is doing the majority of people a disservice.

Date: 12/3/2005 7:59:52 AM
Author: strmrdr
If we consumers want to talk about these differences we are going too.
If it doesnt fit with what some vendors want to push then tough.

Now back to picking diamonds apart for fun and learning :}

who said we couldn't talk about it? if you are referring to johnq offering an opinion that these hair splitting differences can be exaggerated here, i would have to say his point is valid. no one is saying we can't talk about it, we just need to keep it real and remember that the majority of people aren't as crazy about this stuff as we are.

now back to picking diamonds apart for fun and learning

 

[Daniel B]

Wait a minute. . . I think I got it. So LGF''s only pertain to the pavillion (bottom) portion of the diamond and changing them effects the other angles on the pavillion side, and the stars only pertainand and can only effect the crown portion of the stone? So THATS how you can have the same LGF and different star%''s and vica versa, because they''re on opposite parts of the diamond.

Whew, that took me a while. Ima slooow learner

 

[belle]

Date: 12/3/2005 11:06:42 AM
Author: Daniel B
Wait a minute. . . I think I got it. So LGF''s only pertain to the pavillion (bottom) portion of the diamond and changing them effects the other angles on the pavillion side, and the stars only pertainand and can only effect the crown portion of the stone? So THATS how you can have the same LGF and different star%''s and vica versa, because they''re on opposite parts of the diamond.

Whew, that took me a while. Ima slooow learner

yes, you''ve got it now danielb. lgf''s (lower girdle facets) are on the bottom. stars are on the top.

 

[Daniel B]

For some reason I always thought LGF and Stars touched and were connected somehow so if one was tweaked a little then the other got stretched or shortened too as a result. This thread makes a whole lot more sense now

 

[Rhino]

Date: 12/3/2005 9:57:28 AM
Author: belle
that''s no small size. you''ve got the equivalent of at least a 5ct stone there. we can still use your example but i think the size needs to be more realistic. also keep in mind that more often than not, the arrows will be silvery white not all dark.

Both you and strm raise a good point about shrinking the size. The human brain does not perceive contrast the same in smaller objects as it does in larger objects. This is good Belle. Something we''ve discovered through observation testing we''ve been performing between live specimens and virtual is that the size that strm reduced it to is sufficient to judge appearance and see the differences. Making the images smaller is fine too. Good input.

 

[belle]

Date: 12/3/2005 11:32:59 AM
Author: Daniel B
For some reason I always thought LGF and Stars touched and were connected somehow so if one was tweaked a little then the other got stretched or shortened too as a result. This thread makes a whole lot more sense now

you need to keep in mind that every facet is an individual piece. every single one. when a cutter is faceting a stone, each is cut independently of the other. it''s easy in programs like dc to change an entire set of facets (stars..lgf''s..etc.) and their corresponding counterparts but that''s not the way a real diamond is cut. it''s one by one, facet by facet....all individual. the angle of the cut will have an effect on the final outcome but only as an individual piece of the entire puzzle.

 

[strmrdr]

size of the images depends on the resulution of the monitor so there is no way to controll that using jpg or gif images.

Belle I going to have to respectable disagree with you, the idea that all super-ideals are the same serves vendors not consumers.
As more options are becoming available thanks to the tighter ags0 range and improved cutting technology these options should be explored.

Those that wish to explore it at this level should be allowed to without 50000 lines of warnings repeated in every thread from vendors protecting their own interests saying that it dont matter because to some people it does.
If to no one else it matters to me :} therfore im going to talk about it till I get bored and go back to talking about my beloved asschers :}

 

[Rhino]

Date: 12/3/2005 11:32:59 AM
Author: Daniel B
For some reason I always thought LGF and Stars touched and were connected somehow so if one was tweaked a little then the other got stretched or shortened too as a result. This thread makes a whole lot more sense now

Haha... you''re onto it Dan.

Altering lower half (or lower girdle) length on the pavilion affects what is reflected through the stars (on the crown) in diamonds with grade 1 (ideal) or 2 (near ideal) optical symmetry.

These things aren''t discussed much on the forum but the appearance between the 2 stones that strm posted are observable by any layman. I know because we''ve sent out many such comparisons. Some folks didn''t see much of a difference but many did. Everyone''s different. In our emails Dan you''ve already picked out the difference between 2 stones with more minor subtleties than the comparison strm is showing.