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Quote this post and reply to it Post#1 @ 03-21-02 , 10:41 AM


3.3. Main consequences of GIA's illumination model.
To study the fire of a diamond, the GIA group uses an infinitely distant point source, just the same configuration as that shown in Fig. 2. In such a model, a light beam passed through a prism consists of only colored rays at an infinite distance from the prism. Therefore:
* In the GIA model, the probability of observing a green ray is the same as that for any other color. In real diamonds, green rays are observed much more rarely than blue and yellow rays;
* GIA metric for dispersed color light return DCLR is almost independent of dispersion. For example, if we consider a material, the dispersion of which is two times weaker than that of diamond, the DCLR will be almost the same as that for diamond! Moreover, if we suppose that there is absolutely no dispersion in the material of the considered stone, the DCLR not only fails to become zero, but even remains close to the value calculated by GIA (just dispersion, not refractive index). Let us consider green color, which is located in the center of visual color range and red and blue colors lie on opposite sides of the green color, at equal distances on visual spectrum. The deviation of blue and red spots from green spot on registration sphere depends on the dispersion of the material. In any case, these deviations are small enough and almost equal one another *. When calculating DCLR, the GIA team performs summation. As a result, the red and blue rays compensate each other, and their overall mean DCLR is almost equal to that of the central green ray. Then let us change (decrease) dispersion value of material fixing refractive index for green color. The location of all such green spots on the sphere used by the GIA group for registration will not change, and blue and red spots will be closer to green. When calculating DCLR blue and red rays again compensate each other and we will get the same DCLR value as before!
It is clear from the common sense that if dispersion equal zero fire will not appear. Thus, the following questions arise: What is the merit of the GIA's approach from the viewpoint of modeling the fire and what does the DCLR metric actually describe?
(* Important notes.
1) Actually blue ray can be located further from green than red ray, especially when rays refract from diamond at the angle close to critical. It does not influence on DCLR, however it influences on picture really observed. This is one reason why we observe blue color more often that red, and why most frequently observable colors in diamond viewed at close distance - blue and yellow. Here authors consider angles near critical and smaller it on 2-3 degrees (for example range from 16 up to 21 degrees.) At the large angles the refraction losses are sharply increased, and also the beam area changes, that results in sharp loss of intensity and decreasing of possibility to observe any color.
2) The second reason why more often we can see blue and yellow colors when look at diamond from close distance or use photo camera ("Macro" mode) is color mixture properties. Taking range of spectrum from blue to green and adding green color a little we will get cian color as a mixture. The range of spectrum from red to green with addition of the same little amount of green will be mixed into orange. Under real not very bright illumination conditions a human vision will see cian as blue color, and orange as yellow or brown color, not as red. )
We have just shown that the DCLR takes into account fire that does not actually exist. It is also important to show that the DCLR does no take into account fire that does actually exist. The problem is that the GIA’s illumination source produces only one type of rays, namely, those rays normally incident on the table of the diamond. In reality, a ray may be incident on the diamond at any angle. As far as we know, observers usually grade a diamond, holding it in the face-up position. In this case, the fire they observe originates from light incident not normally to the table plane (typical range of incidence angles is 10-15 degrees, with respect to the table normal). Anyone who has a diamond, may observe the fire phenomenon with a source that obliquely illuminates the table of the diamond. Thus, the DCLR coefficient does not take into account a considerable portion of the actual fire, maybe the most of it. This is also due to the fact that the illumination model is inadequate.
As it can be seen, the results obtained by the GIA group contradict practice. The inadequacy of the illumination model is the main reason of this contradiction. A real light source emits rays in all directions. Therefore, not parallel but diverging rays enter the prism (see Fig.3). If the dispersion angle of the material of the prism is less than the divergence angle of the incident light, there are some white rays at any distance from the prism. Moreover, in the most of real cases, the white rays prevail over the colored. Therefore, in practice green rays are observed rarely, and when the dispersion decreases, colored rays disappear, leaving only white-light beam to observe.

--------
You can read full article on
http://www.gemology.ru/cut/english/grading1/index.htm


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Quote this post and reply to it Post#2 @ 03-21-02 , 11:09 AM


ouh Serg,
heavy post.

I need a fresh morning to read this.

s


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Quote this post and reply to it Post#3 @ 03-21-02 , 11:19 AM


S,
Probably you are right. Very heavy.(:
It is little bit easier to read the article from the beginning .

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oh myhead.....
Quote this post and reply to it Post#4 @ 03-21-02 , 11:57 AM


this is why i didn't major in optics,physics, etc etc. makes my head hurt........
i'm glad there are brains out there able to create & comprehend this stuff....
admiration....
mars


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Quote this post and reply to it Post#5 @ 03-22-02 , 02:58 AM


Very interesting. And it'll take a while to digest and work through the implications.


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Another website
Quote this post and reply to it Post#6 @ 03-22-02 , 08:17 AM


. I cannot get the website Garry cited (Russian site in English), but I can get the American site = http://www.cutstudy.com , then go to 'News & Articles' and click the top item.
. Garry's right - print it out (many pages). This is a biggee; I'm still trying to understand the part above and have yet to finish reading the rest (about errors in the 1998 GIA Brilliance article).
I read such in the wee hours, when there are no distractions.

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Quote this post and reply to it Post#7 @ 03-22-02 , 10:19 AM


Quote:
Originally posted by Serg
When calculating DCLR, the GIA team performs summation. As a result, the red and blue rays compensate each other, and their overall mean DCLR is almost equal to that of the central green ray.

Serg:
. As you know, I disagree with your interpretation of GIA's valuation of DCLR. As I read it, they add (1) red spot + (1) blue spot = (2) color spots. Actually each of these data is modified by its size and weighted by the cos*cos function for angular visibility significance, but they include no factor for color (wavelength) so a red spot and a violet spot do not add to a green spot, as by your analysis; they just add as two spots of unspecified color. They can also add a partial or full chromatic flare as a single large spot of undefined color.
. Mathematically, this difference exists between their simple summation formula (with sigmas, p. 183)) and your integral with wavelengths (Sec. 3.3). They are simply adding weighted points WITHOUT REGARD FOR WAVELENGTH, but the size of each point is proportional to dispersion (dispersivity x distance). You say that they are summing the wavelengths too, in which case the dispersivity would, indeed, make no difference, as you say, but that is not the case.
. This is a BIG DIFFERENCE. I hope I have made it clearer here than in our prior private communications; I have had more time to think about how to explain my interpretation.
. Perhaps their light source is an incorrect model, as you demonstrate so beautifully in your article (Sec. 3.1), however, this does not mean that their metric is not as useful as another for evaluating fire.

[Edited by beryl on 03-22-02 at 09:37 AM]

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Quote this post and reply to it Post#8 @ 03-22-02 , 01:03 PM


Thanks Bruce for very good post.

My answer:

1) Page 181“.The combination of point light source and infinite viewing distance yields only dispersed light on observing hemisphere; that is, the result appears as various colored streaks( with no white centers).
These streaks are composed of colored spots showing the final exit directions of INDIVIDUAL rays.”
+ 2) Page 183“That is, DCLR is the sum over all colored streaks, of the sum over all colors( sampled every 10 nm; see again C.I.E., 1963), of the size( area) of each colored streak multiplied times the “Smoothed” brightness(intensity) of each spot along the streak< times an exit-angle weighting factor (..).”
+ 3)You should consider that the area size multiplied by the intensity should remains constant because of the energy conservation low.
= My conclusion

Is it enough?


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Quote this post and reply to it Post#9 @ 03-22-02 , 09:00 PM


Serg:
. I will review your latest comments. Sorry; I think slowly.
. Comment coming on second part of your post - later tonight, I hope.
. It has been years since I enjoyed technical discussions like these. Delightful; thanks for the opportunity.


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Serg part 2 - GIA light source
Quote this post and reply to it Post#10 @ 03-23-02 , 06:00 AM


Quote:
Originally posted by Serg
GIA’s illumination source produces only one type of rays, namely, those rays normally incident on the table of the diamond. In reality, a ray may be incident on the diamond at any angle. As far as we know, observers usually grade a diamond, holding it in the face-up position. In this case, the fire they observe originates from light incident not normally to the table plane (typical range of incidence angles is 10-15 degrees, with respect to the table normal). Anyone who has a diamond, may observe the fire phenomenon with a source that obliquely illuminates the table of the diamond. Thus, the DCLR coefficient does not take into account a considerable portion of the actual fire, maybe the most of it

. GIA's is a 'reverse-ray' analysis, typical of the illustrations in your DiamCalc!
. Their light-source ray is analogous to the reverse ray to the viewer's eye in the face-up position.
. Their scattered emission rays are analogous to the corresponding color sources in the white light sources, as illustrated in my post #76852, Sep 13, at http://www.diamondring.com/forums/s...ead.php?t=9915.
. If you believe in reverse-ray analysis then you believe in this approach.
. I agree that they must not count rays within the first 10° from normal because, in the reverse condition, these sources would be blocked by the viewer's head. However, their 'best' results just border this condition, as shown on the plot in my post#105367, Feb 02, at http://www.diamondring.com/forums/s...ad.php?t=12719. Accordingly, this error does not affect their 'best' . If you do not believe the validity of these plots, as some have indicated, then forget only this aspect of the discussion - that their inclusion of the first 10° does not affect 'best' results.



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Quote this post and reply to it Post#11 @ 03-23-02 , 06:24 AM


Reverse-ray analysis is a tool.
GIA and we use this tool in absolutely different ways.

We could discuss with you for what reason this difference is a very important. I suggest doing this when we complete the current topic. Otherwise, we would have a lot of questions raised, but not a lot answered.

Did you agree with my statement, that GIA method on DÑLR index calculations resulted in the independence of the index on the dispersion of the stone?
Let me know if you need the additional clarifications on this matter.


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Quote this post and reply to it Post#12 @ 03-23-02 , 06:53 AM


Bruce,
Imagine that somebody decides to help you in your garden and while doing this he damages your plants with your spade. What kind of conclusions will you make? Will you stop entrast your garden to your spade or will you stop entrust your garden to this person? The tool can be used in good or a poor way depending on who is using it.

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Quote this post and reply to it Post#13 @ 03-23-02 , 07:02 AM


Sergey:
. I don't understand your analogy. Please speak more specifically.

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Quote this post and reply to it Post#14 @ 03-23-02 , 08:56 AM


Bruce,
I will try to illustrate my statement about the incorrectness of DCLR index calculation with the story of DCLR formula development.
At the first time I was informed about the formula on DCLR calculation on November 29th, 2000. Yury and I met with Ilene Reinitz and Mr. Ronnie Guerts in Moscow. I was asked to tell nobody about this formula until the publication of GIA article on Fire. Now I can tell about it.
The formula, which was originally communicated to me by Ilene Reinitz at that time, differed from the published one by three matters:
1. Designation of the summation indices (integration, it seems the original formula used integral). Inner summation was made not by colors but by wavelength. Outer summation was made not by "streaks", but by the surface of the upper hemisphere.
2. There was no function Weighting Factor=Cos*Cos.
3. There was no function Smoothed Intensity. The simple Intensity was used.
Below I will try to render the dialogue, which took place during the meeting. I can not guarantee the exactness of phrases, but hope that the general content is conveyed correctly.
Ilene: Sergey, what do you think about our formula?
Sergey: It is awful. It does not have any relation to Fire.
MR.Ronnie Guerts: Why do you think so?
Sergey: Firstly it does not assess what a man sees, it evaluates what has went out of the stone. Secondly the observer profile is not taken into account.
MR.Ronnie Guerts: (Addressing to Ilene) Look, this is what I told you several times. (Start to talk to each other sprightly).
Ilene: (Addressing to Sergey) You do not understand, this is a very good formula.
Sergey: OK, let's approach it in a different way. Assume that you integrate not by the upper hemisphere, but by whole sphere. In this case you will get a constant. This constant will not change when you change the diamond parameters, because the value of this double integral equals the total energy went out from the diamond in visible range. And this is constant.
Ilene: You do not understand. When the article is published, you will understand how good is formula.

Do you agree that the formula described above (one presented in Moscow) actually calculates the light energy in visible range, went out from the diamond within the integration area? And correspondingly has no relation to Fire?
I assume that as an engineer you will easily agree with these statements. Therefore I proceed to the explanation about the results of this formula modification. Let's consider them in the following order.
1. Designation of the summation indices (integration, it seems the original formula used integral). Inner summation was made not by colors but by wavelength. Outer summation was made not by "streaks", but by the surface of the upper hemisphere.

This is just a cosmetic modification. In reality GIA sums by wavelength. To make this look correctly, they are using point source located at infinity and an observer located in infinity. As a programmer you will easily understand why they are doing this. It is much easier to sum by wavelength using the superposition principle, than convert wavelength into the real colors and sum by colors. To get colors it is necessary to analyze all rays, which can fall into a certain point of the sphere. This increases dramatically the time necessary for calculation and requires much more memory. It is also necessary to know how to convert the wave length sum into XYZ, and then XYZ into RGB. And even this will not be enough.

Conclusion: At this stage the integral calculates just energy and does not have any relation to fire.
2. There was no function Weignting Factor=Cos*Cos.

The addition of this function allowed to analyze the distribution of the energy, which went out from the diamond regarding the vertical axis depending on parameters of diamond. But at this stage DCLR function did not start to analyze Fire as it did not do this at the previous stage.
3. There was no function Smoothed Intensity. The simple Intensity was used.

If DCLR function described Fire, it would do it for both Smoothed Intensity = Intensity, i.e. when correction Smoothed was absent.
Summary: Garbage in / Garbage out. GIA did not manage to transfer the formula for the outgoing energy into the function for analyzing Fire.
I am already not trying to convince GIA, but I would like to convince you, Bruce. If my present attempt is not successful, could anybody help me to convince Bruce or help Bruce to convince me.








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Quote this post and reply to it Post#15 @ 03-23-02 , 12:50 PM


Sergey:
. Wow - heavy stuff, as somebody said. I am not looking at this as an engineer or programmer; and I am certainly not a light-physicist like yourself. I am just telling you how I read GIA's formula and that it differs from how I read your interpretation of it. I hope to hear from GIA if either of us is correct - in interpreting what they meant.
. The GIA history is fascinating; thanks for sharing it. I have some stories like that too - some in writing!
. Whether you or they are correct is academic to me, as long as the results of both studies give similar indications, such as "A is bigger than B and C is somewhere between them." As Peter Yantzer says: "Would you rather be right or be happy?" I would rather "be happy" = moving forward toward the goal.
. I think the discussion is too heavy for DT; I had intended to keep it private until you put this thread in DT; it is important for the folks to know only that there are other points of view. Let us continue the discussion now privately.
. It will take me a while to absorb your latest comments (I have no one to discuss it with). You did not explain your gardening analogy above; I am still puzzled what you were talking about.

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Quote this post and reply to it Post#16 @ 03-23-02 , 01:12 PM


Garry:
. I am fascinated by the concept of the viewer's head obstructing source rays. Tell me more (hee-hee).
. I agree completely that this would greatly alter their summation of spots, especially because of the density of them in the area you erased.
. OK; I agree that the method is 'flawed' by omission of this, as was the GIA brightness report of '98. However, this omission is common to all the tests, so perhaps the final COMPARISON of data is unchanged - that "A is greater than B and C is somewhere between them." That's all we really need to know to move forward in deciding which cuts are better than others.
. As a very successful businessman, you know that it's only the 'bottom line' that counts. As for me, I'm having a ball playing with all this - I have nothing to gain or lose -just hope nobody else gets hurt.

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Quote this post and reply to it Post#17 @ 03-23-02 , 11:57 PM


The GIA study uses 10º as a light source to clear the head obstruction or is the light source at 0-360º like in the Garry drawing?, because in the Garry's drawing is an imaginary observer.


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Quote this post and reply to it Post#18 @ 03-24-02 , 04:50 AM


Garry,
Thank for support of idea of public discussion.
4.Point. Open discussions open new people and new ideas better than private .

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Quote this post and reply to it Post#19 @ 03-24-02 , 07:24 AM


. I prefer public discussion in forum. But I know this one interests very few DT readers and some have suggested that such discussions don't belong here.
. I will continue publicly, stressing that there are no personal factors involved, just an effort to get the best truth in the fastest way. I have much admiration for Sergey, Yuri, Vladimir, and Garry.
. Remember, Sergey, that you gave me a copy of DiaCalc because I "was the first to say Tolkowsky was not God". Nor are we.
. I am reading Anton Vasiliev's 1991/95 revised article now, which bears on the same subject but in different terms. In its criticism of the GIA Fire article it supports your claim that dispersion by reverse-ray analysis is not correct.
. On the other hand, this supports my claim that light is not reversible, in our long disagreement on this subject. I begin to think that we agree but that interpretation of words is the problem.
. I wish I could come to Moscow in June, as planned, to discuss these things in fun with beer, but I can't.

[Edited by beryl on 03-24-02 at 06:26 AM]

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Quote this post and reply to it Post#20 @ 03-24-02 , 08:12 AM


Juan:
. GIA does not consider the viewer's head at all, though it typically obstructs about 10° of rays (to either side - see my illustration above).
. Accordingly, their quantitive results are in error in areas where this is a factor, and comparison of these data with those in areas where it is not a factor is numerically incorrect.
. My graphical interpretation of their data, however, shows that what they finally indicate as 'best' is in an unaffected area, so their errors in quantity and comparison of other areas is academic - the corrected comparisons would only more strongly confirm that result.
. I don't care if they made an error in the areas which are unimportant in the final analysis.
. I hope all is well with you, Juan.

[Edited by beryl on 03-24-02 at 07:17 AM]

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Quote this post and reply to it Post#21 @ 03-24-02 , 08:18 AM


Bruce,

Each one way of ray is reversible !
But some consequences are reversible, some consequences are not reversible.

The dispersion angle is not reversible.

Remember about the spade and dilettante gardener .

We will publish this Anton article soon.

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Quote this post and reply to it Post#22 @ 03-24-02 , 08:35 AM


Quote:
Originally posted by beryl
Juan:
. GIA does not consider the viewer's head at all, though it typically obstructs about 10° of rays (to either side - see my illustration above).
. Accordingly, their quantitive results are in error in areas where this is a factor, and comparison of these data with those in areas where it is not a factor is numerically incorrect.
. My graphical interpretation of their data, however, shows that what they finally indicate as 'best' is in an unaffected area, so their errors in quantity and comparison of other areas is academic - the corrected comparisons would only more strongly confirm that result.
. I don't care if they made an error in the areas which are unimportant in the final analysis.


[Edited by beryl on 03-24-02 at 07:17 AM]


Bruce please study the diamond Crown Angle =36 , Pavilion Angle = 39.5. ( You can use your or our ray tracing software)
I think What you opinion about GIA result can be change after this work.


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Quote this post and reply to it Post#23 @ 03-24-02 , 08:54 AM


Sergey:
. I still do not understand your analogy about the garden; unless you explain it, it conveys no message to me.

. I have derived the formula for 'prism angular dispersion' which Anton quotes from V.I.Malyshev, which evolves simply from Snell's Law, so I accept that, but I do not yet see that it proves non-reversibility. I am not yet convinced; I will continue my analysis and perhaps I will understand. If true, it seriously condemns GIA's reverse-ray analysis. Hopefully, GIA will offer comments on this.

. My oiriginal point was that I did not agree with your interpretation of GIA's formula; I must now review that again in light of your latest comments on that subject. I do this because I think you are criticizing GIA incorrectly - on that issue.
. My second point, about reversibility, is different; perhaps they have made a serious error there; I am not convinced yet, but studying it as time and weather permit.
. A third point, which Garry raises, about neglecting head obstruction, is one we all know well, but if it does not affect the final 'best' decision, then it is academic. To me, the data suggest that this is the case.

[Edited by beryl on 03-24-02 at 08:02 AM]

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Re: Serg part 2 - GIA light source
Quote this post and reply to it Post#24 @ 03-24-02 , 09:05 AM


Quote:
Originally posted by beryl
Quote:
Originally posted by Serg
GIA’s illumination source produces only one type of rays, namely, those rays normally incident on the table of the diamond. In reality, a ray may be incident on the diamond at any angle. As far as we know, observers usually grade a diamond, holding it in the face-up position. In this case, the fire they observe originates from light incident not normally to the table plane (typical range of incidence angles is 10-15 degrees, with respect to the table normal). Anyone who has a diamond, may observe the fire phenomenon with a source that obliquely illuminates the table of the diamond. Thus, the DCLR coefficient does not take into account a considerable portion of the actual fire, maybe the most of it

. GIA's is a 'reverse-ray' analysis, typical of the illustrations in your DiamCalc!
. Their light-source ray is analogous to the reverse ray to the viewer's eye in the face-up position.
. Their scattered emission rays are analogous to the corresponding color sources in the white light sources, as illustrated in my post #76852, Sep 13, at http://www.diamondring.com/forums/s...ead.php?t=9915.
. If you believe in reverse-ray analysis then you believe in this approach.
. I agree that they must not count rays within the first 10° from normal because, in the reverse condition, these sources would be blocked by the viewer's head. However, their 'best' results just border this condition, as shown on the plot in my post#105367, Feb 02, at http://www.diamondring.com/forums/s...ad.php?t=12719. Accordingly, this error does not affect their 'best' . If you do not believe the validity of these plots, as some have indicated, then forget only this aspect of the discussion - that their inclusion of the first 10° does not affect 'best' results.



Bruce,

The location of diamond Crown Angle =36 , Pavilion Angle = 39.5 is very close by maximum of Fire ( Figure 12, 60% Table, 50% Star, 75% Lower Girdle ) for Crown Angle =36 .

Do you agree?

Why your red line is far from this diamond?
How do you find your red Line?

Old beryl
 
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Quote this post and reply to it Post#25 @ 03-24-02 , 09:48 AM


Sergey:
. Using GIA's white line of 'best' proportions in Fig.11 (same as Fig.12 for this case), I get about 40.3° pavilion at 36° crown.
. See my post# 105607, Feb 04 for enlarged picture and also my white lines on the chart for 54% table (magenta line on my 10° obstruction chart). Ref. http://www.diamondring.com/forums/s...ead.php?t=12719

[Edited by beryl on 03-24-02 at 08:52 AM]

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