Hey here is the first of many....

[Ellen]

Date: 1/26/2007 5:35:05 PM
Author: Maisiebelle
Ellen thankyou very much for your explanation. I understood what you meant!

Its really weird but when I looked at diamond rings in shops here I didn''t really like the sharp skinny sparkles. Up till I read your explanation I couldn''t explain what I meant about how they appeared to me. Now I''m glad I know what causes it because it reinforces that I need a ring with smaller lgf.

What a relief!

Woohooo!

Get on that phone miss!

 

[Maisie]

EEEK! Its all so fab!

What do I need to do now? Apart from phone obviously lol....

Should I pick out a couple of diamonds that I like and ask about them or just stick with the one I showed you here? Its a big decision to make and I think that because I can''t go and see them in person its going to be a bit scary.

The live consultation thingy that we can use on here might be the best way for me to go about this I think. Then Lesley or one of the others can talk me through things better and I can see if they need to show me something. I wish I lived in Texas or even the US lol!

 

[Maisie]

Just had a great chat with John about the diamond I like. That man really can talk lol!! I feel very happy that I picked a good stone!! Very proud of myself!

Looks like I may lose out on this diamond but he assures me they will be able to find me another one if I do.

Happy happy day!!

 

[Ellen]

Date: 1/26/2007 8:57:11 PM
Author: Maisiebelle
Just had a great chat with John about the diamond I like. That man really can talk lol!! I feel very happy that I picked a good stone!! Very proud of myself!

Looks like I may lose out on this diamond but he assures me they will be able to find me another one if I do.

Happy happy day!!

Sorry nobody was around to answer your previous post, but it seems like you managed just fine without us. And yes, they''ll find you one.

Isn''t it fun?

 

[Maisie]

Yes its the greatest fun! I don''t mind that nobody replied to the earlier post. I know people are busy.

 

[JohnQuixote]

Date: 1/26/2007 8:57:11 PM
Author: Maisiebelle

Just had a great chat with John about the diamond I like. That man really can talk lol!! I feel very happy that I picked a good stone!! Very proud of myself!

Looks like I may lose out on this diamond but he assures me they will be able to find me another one if I do.

Happy happy day!!

 

[JohnQuixote]

I told Maise I would provide some graphics & info about LGFs:

In well-cut diamonds the lower girdle halves impact the character of performance, as others in the thread have described.In general terms broad flashes get more visible as LGF get shorter and needlelike flashes more visible as they get longer.Different configurations are impacted differently, as Garry outlined on page 1, so X% looks different in a small-tabled stone (50%) than it does in a larger table size (>60%), for instance.

For years the lower girdles were somewhat overlooked, except by specialists (like some on this forum).Now both major labs take them into account.The LGF range for GIA EX runs from 67.5% - 87.5%.AGS judges each diamond on its own merits but for diamonds near-Tolkowsky the range overlaps the heart of GIA’s.

Here are some images I prepared for an earlier webinar.You can estimate the LGF% by viewing the ‘arrows;’ those are the pavilion mains.These diamonds are near-Tolkowsky, modeled at 56/40.8/34.7.They assume perfect optical symmetry (good pavilion symmetry enhances the impact of the LGFs).

 

[JohnQuixote]

You can see the size of the pavilion mains well in magnified reflector photos like IS and ASET.

 

[JohnQuixote]

Turning the diamond over, here is what the pavilion ''hearts'' image looks like (assuming perfect optical symmetry).

 

[JohnQuixote]

Maise, about ACA: Each is cut inside a range designed to produce consistent performance & visual balance.I could give numbers but the ranges aren’t hard to figure out and numbers will never be as meaningful as actual observations made after spending time with your diamond; ACA or other.

Date: 1/26/2007 5:29:40 PM
Author: Ellen


strm, my lgf's are 75.6 if I recall correctly, I'd say that's on the shorter end, and NEVER does my table look dark, seriously. I would have sent it back if it did.

I also agree, I can definitely notice the difference in diamonds and how they sparkle. Looking at all the ones I have had in my hands, and all the ones I can scrutenize more closely, as in family, I have seen MANY different looks.

Maise, there is no right or wrong. I'll try to give you an example.

My SIL's stone has longer lgf's, and when her stone rocks, imagine seeing a wave of very fine, skinny, needle like sparkles washing over it. Mine has shorter lgf's, and when my stone rocks, you see some of the smaller sparkles, but intermitently are huge POPS, with a very large, bold flash.

Also, the shorter really put on a show in ambient lighting.

Do a search, there are several good threads that can help you.

And that stone is a knockout.

Ellen’s is a textbook description of the real world performance we set out to achieve with our cutting goals…and I think it’s much more engaging than me blabbing data.

 

[starryeyed]

Date: 1/27/2007 7:58:05 PM
Author: JohnQuixote
I told Maise I would provide some graphics & info about LGFs:

In well-cut diamonds the lower girdle halves impact the character of performance, as others in the thread have described. In general terms broad flashes get more visible as LGF get shorter and needlelike flashes more visible as they get longer. Different configurations are impacted differently, as Garry outlined on page 1, so X% looks different in a small-tabled stone (50%) than it does in a larger table size (>60%), for instance.

For years the lower girdles were somewhat overlooked, except by specialists (like some on this forum). Now both major labs take them into account. The LGF range for GIA EX runs from 67.5% - 87.5%. AGS judges each diamond on its own merits but for diamonds near-Tolkowsky the range overlaps the heart of GIA’s.

Here are some images I prepared for an earlier webinar. You can estimate the LGF% by viewing the ‘arrows;’ those are the pavilion mains. These diamonds are near-Tolkowsky, modeled at 56/40.8/34.7. They assume perfect optical symmetry (good pavilion symmetry enhances the impact of the LGFs).

John, thank you soooo much for this! And thanks for your empirical evidence, Ellen! It's pretty clear that lgf's are a matter of personal preference. A 75% lgf is NOT worse than 80%. From a previous post, it sounded like 75% might be extremely short. Whew! Thanks for clarifying.

 

[strmrdr]

Thanks John this graphic demos what I was talking about.
Forgetting that these are oversize because its the ratio that's important not the exact size that matters.
The shorter LGF% diamond have more dark area than the longer lgf% diamonds and under the table is where it is most visible.
With greater head shadow this is even more apparent.
Therefore the longer lgf% diamonds until you get too long(starting at 85% and apparent at 90% below) then it reverses a little have a better light to dark ratio that is visible at any size.

 

[Maisie]

Date: 1/27/2007 9:20:33 PM
Author: strmrdr
Thanks John this graphic demos what I was talking about.
Forgetting that these are oversize because its the ratio that's important not the exact size that matters.
The shorter LGF% diamond have more dark area than the longer lgf% diamonds and under the table is where it is most visible.
With greater head shadow this is even more apparent.
Therefore the longer lgf% diamonds until you get too long(starting at 85% and apparent at 90% below) then it reverses a little have a better light to dark ratio that is visible at any size.

So if I have a diamond with 75.1% lgf its going to have dark area? That I will be able to see all the time? I wish I was more intelligent - this is really confusing.

Maisie

 

[JohnQuixote]

 

[Maisie]

Thank you for your quick reply John.

Pricescope is a really great place to be. There are so many different people here but the one thing that draws us together is our love of diamonds. When you are new here its overwhelming, there are so many things to consider when choosing the best you can get for what can be an incredible amount of money. This is why I have asked so many questions. I need to learn as much as possible before we take the plunge and buy my ring. Some of the subjects are really easy to understand - eg: colour or clarity. Others are more complex. When you get into the area of lgf or pavillion angles it becomes significantly more difficult for someone like me.

I want to thank everyone who has taken the time to explain (sometimes more than once) the things I don''t understand.

Maisie

 

[WinkHPD]

Date: 1/26/2007 2:44:07 PM
Author: strmrdr

Date: 1/26/2007 2:29:27 PM
Author: Maisiebelle
Aww thankyou both, you are looking after me and I really appreciate it! I have actually seen what I think could be the one (provided its not gone by the time I need to buy it). Would you have a quick look and tell me what you think?

http://www.whiteflash.com/hearts_arrows/A-Cut-Above-H-A-cut-diamond-179732.htm

I know I might miss out on this one as its a couple of months till I can buy it but at least I will know if my choice would be along the right lines.

Thanks

lgf% is too short otherwise its nice.

AAAAACCCCCKKKKKKK!

Okay, I am coming very late to this thread and maybe this has been addressed, but why on earth would you say such a thing? GIA will give its excellent cut grade to stones with lower girdles as low as 67.5% and this stone has one right near the middle of the range for an excellent cut grade by gia.

If it is lower than you like, fine, but to tell someone that it is not a good stone because you like it different is ------------------------- (you pick the word, I am at a loss for the appropriate word). If it was too short, GIA would penalize the stone for it, not reward it with their top grade. AGS also allows this in their ideal range so your comment is just incorrect and -----------------------------. (Still looking for the right word and or phrase.)

Please, let us not make pronouncements about our personal preferences as if they were writ in stone or even scientifically correct.

I will now get to reading the remaining three pages of posts so that I can find out if this has been already addressed. Seeing that it is three more pages long, I am going to guess that it has but this post puts me in mind of the old Snoopy cartoons with Lucy pulling the football out from the foot of our hero and someone off to the side saying "Good Grief!"

Wink

 

[WinkHPD]

Date: 1/26/2007 5:29:40 PM
Author: Ellen


strm, my lgf''s are 75.6 if I recall correctly, I''d say that''s on the shorter end, and NEVER does my table look dark, seriously. I would have sent it back if it did.



And that stone is a knockout.

I snipped out most of the above response because of the sentence that is left. It is actually near the middle of the range, not even close to the shorter end.

GIA publishes the rules for its excellent grade, AGS looks at each stone and as such does not publish written limits for what will be included as ideal, but if they did this stone would be near the center of what they allow in practice.

Ellen, I applaud your willingness to look at the stone and to let your eyes do the talking, I just wanted you to know that this stone is more towards the center than the lower end of acceptable lower girdle lengths.

Wink

 

[WinkHPD]

Date: 1/27/2007 7:59:17 PM
Author: JohnQuixote
You can see the size of the pavilion mains well in magnified reflector photos like IS and ASET.

Nicely done John! Do you perchance have the 40 blue for those ASET pictures? It would be interesting to see the effect that a larger head or a big hairdo would have on those different stones. (For those new to ASET pictures, AGS normally looks at the 30 degree of obscuration and the 40 degree of obscuration referred to as 30 blue and 40 blue when grading a diamond. Some stones that look incredible in 30 blue look REALLY bad in 40 blue as per the example below.

Wink

P.S. Sorry, but I have no information on any of the angles etc on these stones.

 

[strmrdr]

 

[strmrdr]

Date: 1/28/2007 6:48:07 PM
Author: Wink


AAAAACCCCCKKKKKKK!

Okay, I am coming very late to this thread and maybe this has been addressed, but why on earth would you say such a thing? GIA will give its excellent cut grade to stones with lower girdles as low as 67.5% and this stone has one right near the middle of the range for an excellent cut grade by gia.

The same GIA who came up with the GIA cut grade by the trade for the trade says so its right eh?
If the trade wanted to push 40% lgf% GIA would likely support it.

 

[WinkHPD]

 

[Ellen]

Date: 1/28/2007 7:06:03 PM
Author: Wink

Date: 1/26/2007 5:29:40 PM
Author: Ellen

<snip>
strm, my lgf''s are 75.6 if I recall correctly, I''d say that''s on the shorter end, and NEVER does my table look dark, seriously. I would have sent it back if it did.

<snip>

And that stone is a knockout.

I snipped out most of the above response because of the sentence that is left. It is actually near the middle of the range, not even close to the shorter end.

GIA publishes the rules for its excellent grade, AGS looks at each stone and as such does not publish written limits for what will be included as ideal, but if they did this stone would be near the center of what they allow in practice.

Ellen, I applaud your willingness to look at the stone and to let your eyes do the talking, I just wanted you to know that this stone is more towards the center than the lower end of acceptable lower girdle lengths.

Wink

Wink, you''re right. And I knew that, but was basing that statement on stones we see. I should word it better.

Would it be fair to say, in the future, it''s leaning towards the shorter side of "what we typically see"? Because honestly, 74 is the lowest I think I''ve ever seen, in all the diamonds I''ve looked at, in person and online.

 

[WinkHPD]

Date: 1/28/2007 7:30:00 PM
Author: strmrdr

Date: 1/28/2007 6:48:07 PM
Author: Wink


AAAAACCCCCKKKKKKK!

Okay, I am coming very late to this thread and maybe this has been addressed, but why on earth would you say such a thing? GIA will give its excellent cut grade to stones with lower girdles as low as 67.5% and this stone has one right near the middle of the range for an excellent cut grade by gia.

The same GIA who came up with the GIA cut grade by the trade for the trade says so its right eh?
If the trade wanted to push 40% lgf% GIA would likely support it.

If it were just GIA maybe, but when AGS joins the parade, then I don''t think so. AGS has rocked a LOT of boats, and done an excellent job of providing transparent research. If not we would not now have the incredible princess cuts that we now have, but the same bulky "poopy" looking princess cuts we have had for the last twenty or thirty years...

Wink

 

[strmrdr]

Date: 1/28/2007 7:39:57 PM
Author: Wink

Date: 1/28/2007 6:02:58 PM
Author: JohnQuixote

Date: 1/28/2007 5:18:20 PM
Author: Maisiebelle

Date: 1/27/2007 9:20:33 PM
Author: strmrdr
Thanks John this graphic demos what I was talking about.
Forgetting that these are oversize because its the ratio that's important not the exact size that matters.
The shorter LGF% diamond have more dark area than the longer lgf% diamonds and under the table is where it is most visible.
With greater head shadow this is even more apparent.
Therefore the longer lgf% diamonds until you get too long(starting at 85% and apparent at 90% below) then it reverses a little have a better light to dark ratio that is visible at any size.

So if I have a diamond with 75.1% lgf its going to have dark area? That I will be able to see all the time? I wish I was more intelligent - this is really confusing.

Maisie

No ma'm. Remember that diamonds are not glued in one position.

1. In motion a well-cut diamond’s light/dark areas reverse themselves.Here are those same sims through a range of tilt (below).
2. Now…go back and disregard #1 because you can change the software’s lighting to change the results.

Those screen shots were only meant to show pavilion/arrows differences. Computer screen shots don't replicate life. We could start a war of software images that won't be helpful with such closely matched diamonds.

This is because our world has multiple light sources.However, even if the lighting and your head were glued in one position, moving the diamond changes everything.Tilt it and the arrows and LGFs swap brightness…tilt it more & they swap again…and so forth.Do it rapidly and you have scintillation.With shorter LGF the ‘broad’ flashes are created by the wider pavilion mains (arrows) flashing brightly.

In the narrow range we’re talking about the short and long configurations have the same visible impact, it’s just distributed slightly differently.

Here again Don Quixote Slays the dragon. Genetically our eyes are hard wired to detect edges and contrasts. I will go so far as to say that it is the contrast that makes the diamond beautiful to most of us. AGS was most thourough in their research in this area and the slides showing this are very interesting. When we move the diamond the dark becomes bright and the bright becomes dark and our eyes determine this as the perception of sparkle.

The AGS research even found that the presence of the dark added to the perception of brightness, ie that a stone with the same light return but more 'darkness' in the form of contrast, provided that the contrast was not excessive, was actually perceived of as brighter than a stone with little to no contrast.

This is genetic! It is hardwired into our brains as it gave our ancestors the ability to find the game that was hiding from them. We detect edges, we detect contrast, it fed our ancestors and gives us pleasure with our diamonds and gems.

Storm, I do not doubt that these are not the stones that you like. However, MILLIONS of dollars of research by both GIA and AGS have found in favor of these stones along with the eyes of literally hundreds of my clients. These same MILLIONS of dollars of research have also found in favor of the stones that you DO like.

I know you are not a fan of EightStar because of their shorter LGF's but many people are, and for just the reasons that you do not like them. Many people love the larger more cohesive flashes of brightness and the more visible dispersion. Others like the smaller more jumbled look of the longer LGF's. This truly is a question of taste and the stone you say has too short LGF's is indeed close to the middle of the range.

I was going to say just my opinion, but I realize that is wrong, it is just the result of millions of dollars and several years of research by some of the most brilliant light physicists in the known universe.

Wink

well at least ya admit there is a difference unlike some that have a hissy fit when its pointed out that not all lgf% are the same and think even if they aren't consumers cant tell the difference anyway.
We will have to disagree on short lgf being as good as 77 and longer...

edit to add the word: think
[/i]

 

[WinkHPD]

Date: 1/28/2007 7:43:37 PM
Author: Ellen

Date: 1/28/2007 7:06:03 PM
Author: Wink

Date: 1/26/2007 5:29:40 PM
Author: Ellen

<snip>
strm, my lgf''s are 75.6 if I recall correctly, I''d say that''s on the shorter end, and NEVER does my table look dark, seriously. I would have sent it back if it did.

<snip>

And that stone is a knockout.

I snipped out most of the above response because of the sentence that is left. It is actually near the middle of the range, not even close to the shorter end.

GIA publishes the rules for its excellent grade, AGS looks at each stone and as such does not publish written limits for what will be included as ideal, but if they did this stone would be near the center of what they allow in practice.

Ellen, I applaud your willingness to look at the stone and to let your eyes do the talking, I just wanted you to know that this stone is more towards the center than the lower end of acceptable lower girdle lengths.

Wink

Wink, you''re right. And I knew that, but was basing that statement on stones we see. I should word it better.

Would it be fair to say, in the future, it''s leaning towards the shorter side of ''what we typically see''? Because honestly, 74 is the lowest I think I''ve ever seen, in all the diamonds I''ve looked at, in person and online.

I would be tempted to agree with you, but then I realize that I have never known even a fraction of 1% of the stones that I have looked at LGF''s. I have looked at 10''s of thousands of stones and I have known the lgf''s on maybe 100 of them. It is a tiny part of the puzzle unless they are so far off as to be absurd.

I leave that to the Brian the Cutter and Antwerp Paul types. That is their job to know and relish the details of. My job is to assess the overall affect of what they have done and I do that with my eyes with the tools that I use to confirm my eyes being really my second line of defense. I reject or accept first with my eyes, only then do I even consider looking at paper and tools.

Wink

 

[WinkHPD]

Date: 1/28/2007 7:53:04 PM
Author: strmrdr

We will have to disagree on short lgf being as good as 77 and longer...

That I am okay with. I always like to agree to dissagree when possible. I like them, you do not. That I readily accept.

Wink