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Quote this post and reply to it Post#1 @ 02-03-02 , 04:51 PM


. Those of you interested in the tech end of the cut-grading activity have read GIA's latest article on 'fire' in the Fall 2001 issue of "Gems & Gemology". Watch out: now their plots have pavilion angle increasing from bottom to top = the opposite of how they did it in their brightness data of 1998.
As with that brightness data - see http://www.diamondring.com/forums/s...ostid=#10 2605 - a week ago, I now plot these fire data against "Faceting Limits" to see if there is any correlation or interesting observations.
. The GIA charts, Fig.11 & 12, are for 75% pavilion girdle facet length and 50% star length; Fig.11 is for 60% table, while Fig.12 is for 54% table. They each show two 'ridges' of fire maxima (GIA highlighted them on Fig.11). These data are plotted below on the the 10 head-obstruction diagram.
. It is interesting to note that one ridge is along the edge of the light-shaded area (where reflections from pavilion mains become dark to a normal viewer), and the other is along the edge of the dark-shaded area (where reflections from 75% pavilion girdle facets also become dark). Is this significant?
. Some 'experts' say the GIA data are meaningless and some say my analysis of them is meaningless. So be it; here is my presentation of the GIA data.
. By the way, there are some significant questions about the GIA results: all of the 'chromatic flares' shown in their photos (cover & Fig.5) have full-spectrum of color; they say you see only one color because your pupil is small. What of our discussions of last Summer, and GIA's Research article "Diamond Optics Part 2". July 20, where we saw that, near critical angle, only the red end of the spectrum is refracted out, and that some dispersed rays are separated by hitting adjacent edges of a facet join within the gem? These would not show full spectrum. I have asked GIA but no response yet (busy re Tucson Show, no doubt).



[Edited by beryl on 02-03-02 at 03:53 PM]

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Enlarged View
Quote this post and reply to it Post#2 @ 02-03-02 , 04:57 PM


. Here is enlarged view of the plot area.
. Jamesd: I expect to hear from you on this. I think your intimation of stereo effect may apply.



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Quote this post and reply to it Post#3 @ 02-04-02 , 07:04 AM


. Sorry; I meant to clarify that the diagonal-shaded zone is for table-bezel rays (& vice-versa). Also, "FL" charts are only for doubly-reflected rays (no rays with extra internal bounces) which are all in planes through the gem's axis. It is encouraging, however, to note how much this simple analysis has revealed/explained in the past.
. The region for bezel-to-bezel rays is much lower than this pic; there are no bezel-to-bezel rays in typical round brilliant-cut diamonds.

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Quote this post and reply to it Post#4 @ 02-04-02 , 07:42 AM


. Here is Fig.11 of GIA fire article, which is for 60%T (table), showing only the chart for 75%LG (lower girdle) and 50%S (star). Note the ridges indicated in white by GIA. I have added the black rectangle, which is the range shown on my charts above.
. Darker red = more fire. Note that it increases as pavilion angle decreases and crown angle increases - along the infamous 4:1, 5:1, or 6:1 diagonal; the greatest fire does not even occur on typical brilliant-cut diamonds!



[Edited by beryl on 02-04-02 at 07:21 AM]

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Quote this post and reply to it Post#5 @ 02-04-02 , 07:47 AM


... and here's GIA Fig.12, for 50% table (same lower girdles & stars). I added the white 'ridge-lines' on this one.
. Hey, Marty, look - they show pimples & dimples on this chart!Good luck in your presentation at Tucson this week.

. By the way, for those of you with a copy of the article, the center caption of Fig.14 should say 'DCLR', not 'WLR'.
. Again I ask where are the individual color rays we see on DiamCalc models? GIA photos do not show them.
. Oops: just noticed that 10 notation is missing at angle between incident and reflected rays at head on 1st illustration of this thread.

[Edited by beryl on 02-04-02 at 07:16 AM]

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Quote this post and reply to it Post#6 @ 02-04-02 , 02:33 PM


Thanks. I've only just read these so I want to let them stew for a da or three and read and ponder a few times before commenting much.



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Quote this post and reply to it Post#7 @ 02-04-02 , 09:33 PM


Jamesd:
. I can relate to that; most things come to me days later - often while yardening.
. "Faceting Limits" came out of a beer mug the day after I noticed a gem turn dark as I brought it closer to my eye.
. That traditional cuts are on the edge of the shaded diagonal is because of the contrast it produces between mains and halves never occurred to me. Garry Holloway pointed it out 26 years later!
. So I'll wait for your comments. There are some truths lurking here.

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Quote this post and reply to it Post#8 @ 02-05-02 , 05:43 AM


lurk.
S

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Quote this post and reply to it Post#9 @ 02-05-02 , 07:28 AM


Garry & Iiro:
. Constructive comment would be better.

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Quote this post and reply to it Post#10 @ 02-05-02 , 07:40 AM


Sorry Bruce,

I have not yet read this thread propely.

I will, but a bit later.

S

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Quote this post and reply to it Post#11 @ 02-05-02 , 09:03 AM


Iiro:
. This sort of thing needs inspiration from people of various viewpoints, as in a 'brainstorming' session; hopefully someone will see something significant. That is why I do it in forum. John Archer spurred a progress last Spring.
. 'Lurking' may be old-fashioned; it means 'hiding, waiting to come out'. I was raised by my English-teacher grandmother and learned lots of old and uncommon words. I try not to use them.

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Quote this post and reply to it Post#12 @ 02-06-02 , 04:34 AM


Garry:
. Thanks for response and pics. You must give credit when you copy pics like these - MSU, I suppose. Where is the light source?
. I agree that these pics are spots of light, not necessarily dispersed, and thus have nothing to do with 'fire'. It is only when the spots are separated color components that we have 'fire' - as shown by DiamCalc ray-tracing. That is what I find missing in the GIA photo and virtual pattern.
. One more time: head shadow is not obstruction.
. What do you see in the little red pic that I don't? Humorous, I suppose.

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Quote this post and reply to it Post#13 @ 02-06-02 , 06:00 AM


Quote:
Originally posted by beryl
Garry:

. One more time: head shadow is not obstruction.


Bruce,
head shadow is obstruction.

Garry uses reverse of a ray(or logic). (But does not speak about it) . He shows where should be a source of light for supervision of Fire

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Quote this post and reply to it Post#14 @ 02-06-02 , 11:23 AM


Sergey:
. See my thread "Head Shadow is not Obstruction" = http://www.diamondring.com/forums/s...ead.php?t=10173 post#79181+, 9-28-01. That is more than 3 months ago!
. I see a difference, and explain it there; I felt it necessary when I realized that the word 'shadow' caused GIA's misunderstanding of the concept.
. I understand that Garry is using the reverse-ray logic.
. I know you think GIA report is wrong. I think it has errors. Nevertheless, I consider that it may have merit and show their data in relation to "Faceting Limits", that's all. It is curious that their ridges line up with those limits and perhaps someone will see a significance there. I am not smart enough to say who is right (if any) and who is wrong (if any); I just try to compare everybody's results and hopefully find similarities and reasons.

[Edited by beryl on 02-06-02 at 10:37 AM]

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Quote this post and reply to it Post#15 @ 02-06-02 , 11:44 AM


Quote:
Originally posted by beryl
Sergey:
. See my thread "Head Shadow is not Obstruction" = http://www.diamondring.com/forums/s...ead.php?t=10173 post#79181+, 9-28-01. That is more than 3 months ago!
. I see a difference, and explain it there; I felt it necessary when I realized that the word 'shadow' caused GIA's misunderstanding of the concept.
. I understand that Garry is using the reverse-ray logic.
. I know you think GIA report is wrong. I think it has errors. Nevertheless, I consider that it may have merit and show their data in relation to "Faceting Limits", that's all. It is curious that their ridges line up with those limits and perhaps someone will see a significance there. I am not smart enough to say who is right (if any) and who is wrong (if any); I just try to compare everybody's results and hopefully find similarities and reasons.

[Edited by beryl on 02-06-02 at 10:37 AM]

ok.
head blocking is obstruction.
I mean head blocking always.


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Quote this post and reply to it Post#16 @ 02-06-02 , 11:51 AM


Garry:
. The subject of fire and recombining of colors to make white light was discussed in "Yet Another HCA Question" = http://www.diamondring.com/forums/s...35&pagenumber=2 starting at post#71662 by VanGraff on 8-20-01.
. It was discussed even better on July 20 by GIA in their Research article "Diamond Optics Part 2: Light Dispersion, Color Wavelengths and Fire" (I am embarrassed that I had not read it when I said the same stuff to Juan).
. You and Sergey keep telling me "Where's the green?". I do not know. When will you tell me and the rest of us?

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Quote this post and reply to it Post#17 @ 02-06-02 , 02:01 PM


Quote:
Originally posted by beryl

. It was discussed even better on July 20 by GIA in their Research article "Diamond Optics Part 2: Light Dispersion, Color Wavelengths and Fire" (I am embarrassed that I had not read it when I said the same stuff to Juan).

. You and Sergey keep telling me "Where's the green?". I do not know. When will you tell me and the rest of us?


Dispersed rays spread out more widely as the length of the light path increases. A beam of spreading white light begins as a tight bundle of white light, then becomes a bundle of mostly-white light with some colors around the fringes (figure 5, left), and then fans out into the spectrum we are familiar with (figure 5, right) [Footnote 4]. Therefore, the longer the light path, the more chance there is of seeing different spectral colors.

Diamond Optics Part 2: Light Dispersion, Color Wavelengths and Fire
Barak Green, Ilene Reinitz, Al Gilbertson, Mary Johnson,
and James Shigley

http://www.gia.edu/giaresearch/diamond-cut5.cfm




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Quote this post and reply to it Post#18 @ 02-06-02 , 05:48 PM


Sergey:
. I know that, and I listed the reference. Why do you and Garry keep telling me "Where's the green?". It shows clearly in the chromatic flares of GIA Fig.5.
. You two have me very confused; what is the problem? Apparently you two know what you're talking about, but I do not = no communication.

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Quote this post and reply to it Post#19 @ 02-06-02 , 06:24 PM


beryl,

One thought on green. It's a narrow part of the spectrum so on average you'll see less of it because there is less of it in the source and also because the viewing angle is going to be smaller.

Next step, how much green is there in normal lighting conditions? It's not usually considered an attractive color so yellow, red and perhaps blue are more likely to be favored in lamp designs (things like selecting phosphor materials for fluorescent lamps).

One other note from http://www.gia.edu/giaresearch/diamond-cut5.cfm . It notes that "In completely diffused lighting, light strikes the diamond evenly from everywhere and from all angles. Although this type of lighting may highlight the brightness of a polished diamond, the more evenly diffused it is, the more it will suppress fire", which seems effectively what has been written here many times: that the fire comes from the dark areas.

If anyone with a jewelry store still has fluorescent lights, perhaps this may be an incentive to get rid of them so your diamonds look more firey... they mask the fire caused by your spot lighting.

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Quote this post and reply to it Post#20 @ 02-07-02 , 04:16 AM


Quote:
Originally posted by beryl
Sergey:
. I know that, and I listed the reference. Why do you and Garry keep telling me "Where's the green?". It shows clearly in the chromatic flares of GIA Fig.5.
. You two have me very confused; what is the problem? Apparently you two know what you're talking about, but I do not = no communication.

Sorry. We shall publish detailed explanations on our site soon

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Quote this post and reply to it Post#21 @ 02-07-02 , 05:41 AM


Jamesd:
. I have considered that green has approximately the same RI as white light and would therefore be masked by it.
. Sergey & Garry keep teasing me with this but have not given me the answer. I want to know and think everybody should if it is important.
. In our store we also avoided fluorescent light on the opals because it did not show their more valuable 'plays of color'. In my Adult Ed. course my colored stones looked terrible in the school lighting, especially the amethysts.

Sergey:
. I hope your answer comes soon, so all can be aware of it.
. How do we know when new information appears at your website?

[Edited by beryl on 02-07-02 at 04:50 AM]

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Quote this post and reply to it Post#22 @ 02-07-02 , 05:49 AM


Quote:
Originally posted by beryl
Jamesd:
. I have considered that green has approximately the same RI as white light and would therefore be masked by it.
. Sergey & Garry keep teasing me with this but have not given me the answer. I would like to know and think everybody should if it is important = no time for games.
. In our AGS store we had to avoid fluorescent light on the opals because it did not show their more valuable 'plays of color'.


Bruce, You are wrong. We do not tease you.
I have given you brief explanations. As they were not understood I now I write detailed explanations. After the ending of the given work it will be published

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Quote this post and reply to it Post#23 @ 02-07-02 , 05:55 AM


Sergey:
. I was editing my post while you were replying. Note last question.

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Quote this post and reply to it Post#24 @ 02-07-02 , 05:59 AM


Quote:
Originally posted by beryl
Sergey:
. I was editing my post while you were replying. Note last question.


We shall try to publish article the next week. We shall inform about it on a forum DT

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Quote this post and reply to it Post#25 @ 02-26-02 , 11:53 AM


Quote:
Originally posted by Serg
Quote:
Originally posted by beryl
Sergey:
. I was editing my post while you were replying. Note last question.


We shall try to publish article the next week. We shall inform about it on a forum DT


Bruce,

we have just posted our new article:
http://www.cutstudy.com/cut/english/grading1/

We hope you will enjoy.

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