Minor Facets = Minor Effect

[Garry H (Cut Nut)]

Jonathon just mentioned this issue in another thread, and I just wanted to jump down his and all the others who spread or exaggerate this idea.
This includes the GIA who never said much in their article about the subject(because that gets seriously edited and what they say there must be acceptable as fact to the G&G editors). All the missinformation has been spread in a hearsay way.

Anyway enough soap boxing

Here are the Diamcalc2 results for the standard default stone with adjustments to upper and to lower facets seperately.

 

[Iiro]

I made the same test. It looks like minor facets no not change much of brilliance values in DC.
But DC dosent tell anything about Fire or Scintillation. Would they make different result?


PS. I still do not understand anything of Sergs paper about large diamonds.

 

[Garry H (Cut Nut)]

Hi S

The stone in the lower left with lowest values would have more apparent fire, but probably less interesting scintillation.


Re Sergey's work - it is a real brain drainer.
I think i am 1/2 way to understanding it.

 

[elmo]

----------------
On 8/26/2003 1:18:12 AM Cut Nut wrote:

Jonathon just mentioned this issue in another thread, and I just wanted to jump down his and all the others who spread or exaggerate this idea.
----------------

I thought it was the difference between an h&a and an 8*, or in your terms the difference between a "new line" and an old fashioned ACA. I'd agree in the big scheme of things that the difference is getting close to negligible

, but I expect to many folks it's still debatable how minor the effect is.

 

[DBOF]

How can 2/3 rd`s of the facets on a diamond be minor anyways ?

Looks like the majority. All the facets matter and effect how the diamond *looks*, otherwise they wouldn`t be there at all. Single cuts don`t look like full cuts do they ?

Can`t ignore the majority, I mean minority . Facets can vary in size, length,placement, etc, this effects how the diamond *looks* as well.


Brad

 

[Garry H (Cut Nut)]

Its a funny thing Brad, but the minor facets are actually connected by diamond to the major facets if you can get my drift.

The crown angle variation in upper girdle facets in the eg's from 40% to 60% are 39.87 to 42.9 - which sounds a lot - but the steeper facets end up taking up less surface space, so there is no great difference caused.

the lower girdle pavilion angle difference is less - 42.09 to 41.7 respectively - very small = 0.39 degrees. This has a greater effect again mainly because the size of the shorter star facets as seem from the face up view gets larger. But this makes the stone display more fire.

So it is all just swings and round-abouts.

Minor effects.

 

[Iiro]

Serg should step out and explain the first diagram (chart). I need to know what he means with all the data in it.

 

[Serg]

Sibelius,

In present paper we consider diamonds as optical system through which one can observe primary and secondary light sources. One of the important characteristics for grading such an optical system is the probability of observation of a primary light source at a certain or higher brightness.

It is the plot you mentioned, that is to demonstrate the probability dependence upon the quantity (size) of diamond facets. The plot is so far to be used to analyze the phenomenon, not for quantitative calculations, because we didn’t yet finished with developing the adequate mathematical model.

 

[Iiro]

Hi Serg,

Good have some explanation. I understud the firs paragarph of your reply, but the second is a bit confusing.

In this chart, what is the meanining of the left vertical row of numbers?

 

[Serg]

----------------
On 8/27/2003 12

3:41 PM Sibelius wrote:


In this chart, what is the meanining of the left vertical row of numbers?


----------------

The effective total angular size (ETAS)of beams have been emerged out
from diamond for BackRayTracing.

A diamond can be considered as a device that splits a light beam into several smaller (secondary) beams .

 

[Garry H (Cut Nut)]

Every now and then i pull out a printed copy I have in my breif case and read this again Sib.
Do not feel any more stupid than me (which might be an insult to you

) because this is very hard stuff for normal humans (easy for gifted Russian scientists).

A diamond crown can be considered to be a set of windows (but not perfect windows - there is some reflection and not all the light gets in or out).
Its pavilion is a set of mirrors of varying efficieny, that should reflect most light back to the crown 'windows'.

When lights of varying intensity are shining on the diamond with 57 facets then it is possible to see, with a human eye, a certain number of more intense sparkles. Sergey is using very complex and adacned maths modelling 'estimations' to predict the number of sparkles that could be seen.

The chart shows the results for a 10mm diamond viewed from 1/2 a metre (20 inches) that is illuminated from a light 3 meteres ( 10foot) away.
The lower scale is the number of predicet bright facets an observer would see for varying amounts of intensity.

The effective total angular size (ETAS) means that if the number is higher (up the left hand scale) that the ray would have been split up into a more firey display.

Now I am sure that is not all correct - but Sergey can perhaps help us all with corrections.

(I apologose in advance for being a poor student Sergey, but you know the desire to learn is genuine.)

 

[Iiro]

I an earlier post Yuri explained the 1=10 on right side.
It was this:
----Quote Yuri:
I = 10 % means: no more than 90 % of attenuation of source brightness because virtual facet acts as diaphragm.

In the most cases this attenuation will be less because the maximal attenuation is achieved on border of a light cone.
----

To make that in undertstandable Finnish this is my translation:

Every virual facet dimm the original source of light. Blue curve at the top tells the treshold for virtual faces which can emit more than 10 % of original beam back.


Is this completely wrong?


Now Serg tell the right side is :
-------Quote Serg:
The effective total angular size (ETAS)of beams have been emerged out
from diamond for BackRayTracing.

A diamond can be considered as a device that splits a light beam into several smaller (secondary) beams .

-------

The second sentence was understandable but I still do not understand what is "Effective total angular size"?? ETAS??

Let me try. As diamond splits the original beam to smaller ones, the smaller ones can be measured as "Effective total angular size" (ETAS).

How do we read this ETAS? Bigger the better? More the better? Serg told the left hand values are ETAS. Garry tells the higher in left hand value the higher the angle = more fire or more spread in beam to show the rainbow colors.



What does ETAS value 1,00 E - 04 can possibly mean? It is not an angle, what is it?

I am sorry ask all these questions, this makes me look am a bit thick, but so far I have understud most of all tech talk, this time I do not follow.

 

[Garry H (Cut Nut)]

I only have 2 seconds Sib.

The numbers are eg 3 x 10 to power of -4
eg 0.0003

Mathematicians do not know we do not understand their language

But they can still be nice people

 

[Iiro]

Thanks for 2 seconds but still I dont understand 1,00 E - 04

 

[Garry H (Cut Nut)]

.0001

 

[Iiro]

Aha,

so 0,00 E + 00 is = 0

 

[Serg]

----------------
On 8/26/2003 8:32:54 AM Cut Nut wrote:

Its a funny thing Brad, but the minor facets are actually connected by diamond to the major facets if you can get my drift.

The crown angle variation in upper girdle facets in the eg's from 40% to 60% are 39.87 to 42.9 - which sounds a lot - but the steeper facets end up taking up less surface space, so there is no great difference caused.

the lower girdle pavilion angle difference is less - 42.09 to 41.7 respectively - very small = 0.39 degrees. This has a greater effect again mainly because the size of the shorter star facets as seem from the face up view gets larger. But this makes the stone display more fire.

So it is all just swings and round-abouts.

Minor effects.
----------------

There are 2 different correct statements.

1. Big changes of Minor facets can strongly affect to stone beauty.
2. For most of good and classically* polished stones the change of Minor facets parameters has small possible amplitude and Minor facets are hard tied to Main facets position. In these conditions position change** of Minor facets weakly influences to stone beauty.

* Big (more than 1 degree) deviation from classical azimuths of any facets can lead to big changes of stone beauty, because the raytracing is changed entirely.

** It is absolutely incorrect to interpret this statement as "Minor facets are not important for stone beauty". Undoubtedly, they are important. People who make statements about unimportance of Minor facets play on words. They change correct statement "Small changes of Minor facets influence to stone beauty weakly" to absurd statement "Minor facets are not influence to stone beauty". It is dishonest move which misleads consumers.

PS. Both main statements about Minor facets have the right to existence and professionals use it. Professionals who render different services choose more convenient wording. At the same time professionals who really understand this problem, give correct wordings of "contrary" interpretations.
For consumer it is important to understand what wording is correct for concrete set of stones. And it is absolutely incorrect to think, that there is wording which is correct for any case.

Similar "problems".
The glass is full half - the glass is empty half.
We can judge about stone beauty by Sarin data - we can't judge about stone beauty by Sarin data.
Diamond is symbol of love - diamond is mere formality.
There is principal difference between VVS1 and IF - There is no principal difference between VVS1 and IF.

 

[Garry H (Cut Nut)]

Certainly Sergey extreme variations in minor facets (e.g. lower girdles 90%) will cause big problems - but since there is no great reward in weight retention -- and a big penalty in sale price - we almost never see such a problem.

However as you point out - there are stones with twisted facets (azimth) and symmetry faults (like out of roundness) that cause far greater problems.

Those who disagree with my claims - please to go out of your way and find lots of examples to prove me wrong.

The only examples I see are the girdle cheated stones (opposite upper girdle / girdle tweaking to 8* and ACA newline).

Perhaps those who have the gIA Fire article where claims were made would like to re read the article and focus on the actual wording used. and look at the scales on the graphs presented.

 

[Serg]

----------------
On 8/29/2003 7:45:30 AM Cut Nut wrote:

Certainly Sergey extreme variations in minor facets (e.g. lower girdles 90%) will cause big problems - but since there is no great reward in weight retention -- and a big penalty in sale price - we almost never see such a problem.

However as you point out - there are stones with twisted facets (azimth) and symmetry faults (like out of roundness) that cause far greater problems.

Those who disagree with my claims - please to go out of your way and find lots of examples to prove me wrong.

The only examples I see are the girdle cheated stones (opposite upper girdle / girdle tweaking to 8* and ACA newline).

Perhaps those who have the gIA Fire article where claims were made would like to re read the article and focus on the actual wording used. and look at the scales on the graphs presented.
----------------

Garry, Please read my text fully .

Did you read :"
2. For most of good and classically* polished stones the change of Minor facets parameters has small possible amplitude and Minor facets are hard tied to Main facets position. In these conditions position change** of Minor facets weakly influences to stone beauty.

* Big (more than 1 degree) deviation from classical azimuths of any facets can lead to big changes of stone beauty, because the raytracing is changed entirely."

 

[Garry H (Cut Nut)]

i.e. we are agreeing Sergey

 

[Rhino]

I am not in disagreement either and Serg is making my point exactly. We have NO crystal ball to look into to see whether a person is looking at a diamond with 75% lower girdles or 85% lower girdles and there is no crystal ball to tell us how much variance there are in the cutting of both major and minor facets. As Sergey has pointed out variances over 1 degree can greatly influence the optical results of any given stone.

This is why when consumers come on this board with the basic Sarin information and are seeking to know "how their potential diamonds looks" and want to know information regarding the seperate components of brilliance, fire and scintillation it is impossible to assess those components without knowing the details on the minor facets AND the variances to which all the facets have been cut.

Being a distributor and gemologist I get to see many many different flavors of AGS "0" stones cut to a very wide array regarding the minor facets. Some factories around the world I can almost tell you what their minor facet measurement will be due to that particular factories cutting style then there are factories cutting AGS "0" stones whose minor facet cutting vary all over the place. To assume we can predict total light output of a diamond and NOT KNOW all the facts ... well ... I wouldn't drop my hard earned cash unless I know it but that's just me.

All the best,
Rhino

 

[Richard Sherwood]

It is my experience that diamonds with the same major facet proportions will generally produce the same general light return performance with minor facets that fall within the average range of proportions usually encountered.

It is only when you encounter minor facets which fall significantly outside of this "average range" that you see noticeably differently light performances. This is usually the exception rather than the norm.

The minor facets seem to "tweak" the performance of the diamond rather than dictate it. Extremes aside, of course. In my opinion, if you looked at a 100 stones, maybe 5 would fall in the "extreme" range as far as minor facets were concerned.

The major aspects of a stone- light return, light leakage, contrast, fisheye effect, steep & deep syndrome with the "ring of death" are all mostly influenced by the major facet proportions and crown/pavilion angle relationships.

It is my contention that you can get a pretty good "overall" idea of the light performance of a stone from the proportions of the major facets and crown/angle relationship, while the "exact" idea of the light performance is obtained when you tweak the profile of the stone with the minor facet proportions.

The minor facets are the "accessories" which rev up it's performance, while the major facets and crown/angle relationship is the "engine".

 

[DBOF]

Facets can vary in length, size,width and placement. Even the main facets vary, which in turn effects the other facets, they are all connected.

It is a major assumption to assume that 2/3 rds of the facets on a diamond don`t make any important impact on how the diamond looks. They are all playing their part in how the diamond handles light and how it will be *seen*
It is also hard to believe that anyone can predict or assume how a diamond will look visually based on three facet averages and render any meaningful visual predictions without ever seeing the stone itself, This is just plain *blind* science.


Brad

 

[mike04456]

----------------
On 8/30/2003 8

0:53 AM DBOF wrote:
It is also hard to believe that anyone can predict or assume how a diamond will look visually based on three facet averages and render any meaningful visual predictions without ever seeing the stone itself, This is just plain *blind* science.

----------------

There was a time when people found it hard to believe the earth was round. A lot of this cut analysis approaches rocket science but it is still science. Much of quantum mechanics is based on mathematical determinations of things that cannot be directly observed but no serious scientist questions it on that basis alone.

The optical and physical qualities of diamond have been known for many years. Much work remains to be done, but I see no valid reason why a scientifically-based cut grade cannot exist, nor why it should not be possible to predict optical performance based on a knowledge of a diamond's proportions and the lighting environment.

This rising chorus of attacks on cut science remind me a lot of that scene in "The Wizard of Oz," when Toto finally discovers the Wizard, and the big flaming projection responds by bellowing, "Pay no attention to that man behind the curtain!"

There are a lot of vested interested being threatened here...

 

[Richard Sherwood]

-----------
It is also hard to believe that anyone can predict
or assume how a diamond will look visually based on
three facet averages and render any meaningful
visual predictions without ever seeing the stone
itself, This is just plain *blind* science.
-----------

It's not just "three facet averages" though. The main determining factor is the crown to pavilion angle relationship. Even though the minor facets are two thirds of the total amount of the facets, the fact that they are "hard wired" to the major facets will dictate the usual variance of their effect on total light performance, except for that "5%" that fall out of the standard ranges into the extreme ranges.

It's not "blind science" at all, but an educated opinion backed by empirical science. 95% of the time the "blind" profile generated by DiamCalc will fall closely to the stone's actual light return performance. If you happen to have the Sarin info which you can download into the program it will match the stone's performance 100%.

I find that even with matching the minor facet information visually while examining a stone, I can usually match the stones actual IdealScope image almost dead-on with the simulated IdealScope image.

It truly is an amazing program (nice work Serg), which helps the consumer immensely in narrowing down their choices while searching on the internet. Without instruments like the DiamCalc, the BrillianceScope, the IdealScope and now the Isee2, the consumer truly would be shopping "blind".

 

[Serg]

Richard,
Thanks.
It is not my work only.
DC has been develop more than by 4 specialists.

 

[DBOF]

I agree on one thing for sure, this isn`t rocket science at all. The data would have to be more accurate and reliable unless they never want the rocket to lift off, misfire, or land in someones backyard

Numerically driver systems for predicting a diamonds *visual* appearance (fire-brillinace-scintillation) based on exterenal measurements is not accurate enough.
The sarin which is used to provide the numbers is not perfect or accurate in itself. The same stone can have different readings on the same machine and vary from machine to machine. This is where the input is flawed in itself.I have seen many stones with three different readings on sarin that vary quite a bit. This means that the % of accurancy is even lessoned more, since the data iteslf is based on inaccurate external averages. Using facet averages of crown and pavilion and table also does not accurately provide the complete cordinates either. The 8 crown angles and the 8 pavilions are usually not identical, and the table % is based on an average. Any foreign country using this system to launch rockets might send some to the wrong destination

Oh, I forgot we take away the satellite guidance system too. ( seeing the diamond itself )
There are many possibities and ways to cut a round brilliant. One pattern does not fit all. The cutter can vary the size, width, length, and placement of the facets. I have seen many different styles in cutting and they do and can vary, which in turn effects the *look* of the diamond. For instance, I have seen some cut with very skinny pavilion mains as well as wide fat mains. There is no constant, and the ability to arrive at a diamonds complete visual probability based on this mathematical info is flawed. It would need more reliable data, more complete data, and visual observations as well.
Then there are the other 2/3rd`s of the diamond that started this thread.

So if you want to measure every nail in the house to tell you how the house *looks* be my quest. Me, I find it much easier to look at the diamond itself.

Brad

 

[Garry H (Cut Nut)]

In other words Brad, just trust you and consumers should never bother to use their owns nouse or efforts.

HCA is most dependant on the pavilion angle, the most accurate of the measured proportions - because it is the longest facet.

If you really can not add any evidence to support your "trust me" rocket guidance system Brad, why bother typing the words?

And are you still selling lots of those really beautiful diamonds with the 41.6 degree pavilioon angles? The ones you get a great margin on?

 

[DBOF]

I agree Richard, and I respect the amount of work Serg has done along with his professional input

Brad

 

[DBOF]

I`m saying to *look* at diamonds. I had a stone just the other day with 3 different pavilion angle readings from three different sarins, no secret there.The Diamond didn`t change though

I`m sure many in this business have had the same experience.


Brad