Diamond Performance

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"It is also important for the State to inculcate in its subjects an aversion to any 'conspiracy theory of history' for a search for 'conspiracies' means a search for motives and an attribution of responsibility for historical misdeeds."

-Murray N. Rothbard, in The Anatomy of the State



John Swinton [1829-1901] Chief Editorial Writer of the New York Times (Considered "the Dean of his Profession" by his peers), when asked to toast an 'Independent Press' in a gathering at the National Press Club, circa 1880

"There is no such thing in America as an independent press unless it is in the country towns. You know it, and I know it. There is not one of you who dare express an honest opinion. If you express it you know beforehand that it would never appear in print. I am paid... for keeping my honest opinions out of the paper I am connected with. Others of you are paid similar salaries for doing similar things....

The business of the New York journalist is to distort the truth, to lie outright, to pervert, to vilify, to fawn at the feet of Mammon, and sell his country and race for his daily bread, or for what is about the same thing, his salary. You know this, and I know it and what foolery to be toasting an 'independent press.' We are tools, and the vassals of rich men behind the scenes. We are jumping-jacks. They pull the strings and we dance. Our time, our talents, our lives, our possibilities, all are the property of other men. We are intellectual prostitutes."

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

it is always harder to find a "mind clean" stone than a eye clean stone.

_______________________

Travel quote of the week: "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines, sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." -Mark Twain

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"It is also important for the State to inculcate in its subjects an aversion to any 'conspiracy theory of history' for a search for 'conspiracies' means a search for motives and an attribution of responsibility for historical misdeeds."

-Murray N. Rothbard, in The Anatomy of the State



John Swinton [1829-1901] Chief Editorial Writer of the New York Times (Considered "the Dean of his Profession" by his peers), when asked to toast an 'Independent Press' in a gathering at the National Press Club, circa 1880

"There is no such thing in America as an independent press unless it is in the country towns. You know it, and I know it. There is not one of you who dare express an honest opinion. If you express it you know beforehand that it would never appear in print. I am paid... for keeping my honest opinions out of the paper I am connected with. Others of you are paid similar salaries for doing similar things....

The business of the New York journalist is to distort the truth, to lie outright, to pervert, to vilify, to fawn at the feet of Mammon, and sell his country and race for his daily bread, or for what is about the same thing, his salary. You know this, and I know it and what foolery to be toasting an 'independent press.' We are tools, and the vassals of rich men behind the scenes. We are jumping-jacks. They pull the strings and we dance. Our time, our talents, our lives, our possibilities, all are the property of other men. We are intellectual prostitutes."

What you're saying makes complete sense.  If the HOF hearts were smaller the lower girdle facets were longer which 'tunes' the diamond's performance more to direct lighting - like the spotlighting you described.

Lower Girdles

The distance the lower girdles run from girdle to culet determine how thick, or narrow, the pavilion mains are:  Short lower girdles result in wider pavilion mains.  Long lower girdles result in narrow pavilion mains.  On most commercial round brilliants the lower girdle facet average ranges between 75-85% in height, with the majority at the upper side of this range.



In simple terms, short lower girdles (wide pavilion mains like on the left) enhance performance in indirect/soft lighting conditions.  Long lower girdles (narrow pavilion mains like on the right) enhance performance in very bright lighting conditions.  Of course, this assumes robust major proportions and good optical symmetry as a prerequisite. 

Since you were comparing two very fine H&A diamonds I think we can safely make those assumptions.

Here are simulated pavilion/hearts views for diamonds at 78, 80 and 82% lower girdle height.*  This is the view most focused on for ‘A Cut Above,’ as we feel the lower girdle-pavilion main relationships are the single most important factor for light return and visual balance through a broad range of normal lighting conditions.  As Brian Gavin says, “It’s all in the hearts.”

Here are crown/arrows views:



Would you say the other diamond's hearts & arrows more resembled the images to the right of each graphic?  ...If so, it's very logical that the diamond performed well under the spotlights.  Of course, overall configuration has everything to do with the visual balance acquired.

This is 100% correct.  You can find a lot of commercial diamonds cut with long lower girdles.  That's because it tunes them to the selling environment; spotlighting.  This doesn't mean diamonds with long lower girdles can't be made so they're balanced performers - it's all dependent on overall configuration.  Alternately there are some diamonds with very short lower girdles that are more balanced to indirect/soft lighting due to their wide pavilion mains. 

* Your ACA is near the middle of this chart (the 78% LG length number given on your AGS report translates to a 79.7% LG height - which is what I used to generate the graphics).

When designing ACA years ago Brian was been mindful that most peoples' lives take place out of the spotlights.  That's why his prescription for lower girdle height & visual balance = 80% LGH or less on these charts (78.4% LGL or less).  My own diamond comparisons take place mostly indoors/in the evenings at parties and social events, in indirect, soft lighting - or sometimes broken up by spotlights in the host's kitchen - or sitting on barstools enjoying a snifter of Lagavulin.  That's just me, but Brian's formula suits it.  Of course diamonds cut like this can still be 'pop rocks in your eyeballs' in direct light too (I shamelessly stole that phrase from Kenny); it really is dependent on overall configuration.

I have to say again it's not just about lower girdles, but you've chosen a subject that is well suited to illustrate how visual balance is Brian's primary design goal for all ACA (rounds, princess and future cuts).

Ok...That's the LONG story (are you sorry you asked?)

The short story you already summed up:  "there isn't really a set of proportions that can give top performance (and I mean really number 1 here) under all lightings."

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Date: 7/14/2006 12:56:09 AM
Author: Little Star
Hi John, thank you for the long explanation. No, I am still happy I asked. It's always good to learn more.

I remembered there were no splits in the clefts of the HOF's hearts. So my guess is that it's LGH could be nearer to 81%. Btw, did you make a mistake in your statements below:

'When designing ACA years ago Brian was been mindful that most peoples' lives take place out of the spotlights. That's why his prescription for lower girdle height & visual balance = 80% or less on these charts (81.5% LGL).'

I thought LGH (height) are always bigger than LGL (length).

I am still a bit surprised that just maybe a 1% difference in the LGH can result in an observable difference between ACA and HOF. It is pretty obvious that the HOF has more fire.

I have noticed that the stars percentage for ACAs are in general in the lower 50's. I remembered reading somewhere that the ACA specs are in the range 49-51%. How does this affect brilliance and fire for the same LGH?

Sorry for the many questions. I am still learning.

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Date: 7/14/2006 12:57:27 AM
Author: ^

Date: 7/13/2006 11:25:58 PM
Author: JohnQuixote
(are you sorry you asked?)

I'm glad (s)he asked! I'd like to clarify. LGH = Lower Girdle Height. However, WF Sarin report says 'LGirdle Halves', are these synonymous? How do you determine LGL from LGH? Does LGL = LGF? My head is exploding.

Caret, could your head be exploding due to lab classes while pursuing an MBP?

Ok - here's a graphic to explain the Lower Girdle Length vs. Lower Girdle Height and where they are used.  Lower Girdle Length is the one most important to consumers, since both AGS and GIA state this measure on their grading reports (GIA reports it rounded to the nearest 5% however).



As you can see, 75% LGL is 76.9 LGH.  It's really not necessary to know both, but if you work in OctoNus DiamCalc  or read studies conducted by AGSL you'll need to be able to do conversions.  I'll post a chart the guys at AGS provided for this purpose next.

Bill may want to comment here, as I think the Sarin can be programmed to report either.  According to your official AGS report you have 75% LGL.  That translates to 76.9% LGH.  Using LGH the prescription for ACA is 76-80%.  That means your Expert Selection diamond is within typical ACA tolerances.  No surprise since most ES are cut on the same floor as ACA.

Where does indirect performance peak? What spotlighting characteristics are sacrificed the lower you go, is it fire? Is it fair to imagine two linear trends where spotlit and indirect performance cross in an X pattern, and Brian's mark is about the middle of the X while others may put theirs towards the higher spotlit side?

I like that comparison and in that sense yes, Brian designs for the middle of the X.  I think he'd approve of that mental image.  Of course, the range we're discussing is so small it's within a bullseye - and again (sing with me now) - overall performance depends on all of the other configurations.    As for observing characteristics through changing environments, what you see depends on overall parameters (broken record).  Certainly, as the panorama of illumination changes you will note differences.  You said the word sacrifice, others say 'trade-off,' which is ok, but I use balance.  'Sacrifice' sounds like something is lost, but when we're talking about equally premium diamonds tuned differently - a reduction in one aspect sees gain in another.  Does that make sense?

I could go on and on, but I'll let you breathe for a moment.


^

Actually, I need to sleep for a moment!    My cat's already gone to bed.  He's smartish like that.  Pretty good at scrabble too. 

TTYL.

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Date: 7/14/2006 1:02:53 AM
Author: ^
P.S. Can you explain why the size of the Lower Girdle facet affects its character in specific light?

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

it is always harder to find a "mind clean" stone than a eye clean stone.

Wink Jones
GG
Winfield's/High Performance Diamonds

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Date: 7/13/2006 2:54:06 PM
Author: whatmeworry

This is from GIA's study on Fire:

'Across commercial ranges, pavilion angle, lower-girdle facet length, and table size have the largest effect.'

Here's the Link: http://www.gia.edu/pdfs/Fall_2001_Cut.pdf They have some nice graphs that show how their fire metric changes as you change different variables.

However if you want more fire (table smaller, pav angle smaller, etc.), you will be sacrificing brightness. You can't have it all So I think your observation that your ACA is 'whiter' (brighter) than the HOF is a good one. The HOF sacrificed brilliance to get more fire. The ACAs are cut to give a good balance.

Rhino
Good Old Gold

Date: 7/13/2006 8:31:29 PM
Author: Dancing Fire

Date: 7/13/2006 12:15:55 PM
Author:Little Star
Diamond Link

I have no complaints with my Classic ACA. It is indeed a beautiful diamond. However, as part of learning, I have some questions here:

1. I noticed that the diamond performs 'worst' under fluorescent lighting. It is still very white and bright but compared to other lightings, it is clear that the sparkle is not as obvious. May I know what diamond specs (crown/pavilion angles, LGF, etc) would give better performance under this lighting condition?

I appreciate comments from the experts here. Thank you in advance.

that is normal under those lighting condition. everybody expects their diamond (24/7) to look like the fireworks on 4th of july it ain't gonna happen

Rhino
Good Old Gold

Date: 7/13/2006 12:46:33 PM
Author: Ellen
Hi LS.

As to your first question, I know of no one who has ever had their diamond sparkle under fluorescent lighting like in an office. It just doesn't do anything for the diamond.

However, open fluorescent lighting (no cover over the bulbs)set very high in certain stores is a different story. The look will make you giddy. Tower records is supposed to have them. I've found them in certain grocery stores, and a few retail stores. Try looking for them!

As for the HOF showing more fire, it's probably just due it's specific cut. It is said that a higher crown angle produces more fire. However, my crown angle is 34, and my diamond gives off more fire than white light. So, who knows...

I would say, just enjoy your diamond, it's looks like you have a real beauty there.

Rhino
Good Old Gold

Rhino
Good Old Gold

Date: 7/14/2006 12:57:40 PM
Author: Rhino
Hi whatmeworry,

Just reading through this thread and this comment caught my attention...

Date: 7/13/2006 2:54:06 PM
Author: whatmeworry

This is from GIA's study on Fire:

'Across commercial ranges, pavilion angle, lower-girdle facet length, and table size have the largest effect.'

Here's the Link: http://www.gia.edu/pdfs/Fall_2001_Cut.pdf They have some nice graphs that show how their fire metric changes as you change different variables.

However if you want more fire (table smaller, pav angle smaller, etc.), you will be sacrificing brightness. You can't have it all So I think your observation that your ACA is 'whiter' (brighter) than the HOF is a good one. The HOF sacrificed brilliance to get more fire. The ACAs are cut to give a good balance.

Who told you you have to sacrifice brightness for fire or vice versa?

Rhino
Good Old Gold