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Quote this post and reply to it Post#1 @ 05-19-01 , 08:51 PM


http://www.gemtraders.com/research/diamond.html and http://kephra.synflux.com.au/hanh/2...ne/diamond.html give a range of 2.417 - 2.419 for the refractive index of diamond.

Those would correspond to critical angles of 24.440 and 24.418 respectively.

The copy of Tolkowsky's work at http://www.gemology.ru/cut/english/tolkow/tolk1.htm uses 24 degrees and 26 minutes or 24.433 recurring for the critical angle. That corresponds to a refractive index of 2.4176. 27 minutes would correspond to an RI of 2.4161. 25 minutes would correspond to an RI of 2.4191 so it looks as though he used the only whole number of minutes that fits within the right range of RI.

(critical angle = arc sin of 1/RI. Critical angle is the angle at which a beam of light will reflect back inside a surface instead of passing through it.)

In the bits of Diamond Design at gemology.ru Tolkowsky is quoted as using 40.75 degrees (40 degrees and 45 minutes) although he also notes that he knows it permits leakage and that must be considered in the crown design.

Starting with http://www.gemology.ru/cut/english/tolkow/tolk2.htm we have an initial angle of 24 degreees 26 minutes. I'll run through the calculations using angles of 24.440/2.417 and 24.418/2.419 to show the range of results. I'll be calculating with "full" accuracy for intermediate results though I'm writing only to a limited number of digits. Not really sound but the digits are needed to show the degree of variation even though the initial data isn't that accurate...

At 24.440/2.417:

sin RSN = sin(45deg)/2.417 = 0.7071/2.417 = 0.2930

therefore angle RSN = 17.0377 degrees, which is called angle X. later he writes that 4 alpha = 180-17.0377 = 162.9624 so alpha, the pavilion angle, is 40.7406 degrees.

At 24.418/2.419

sin RSN = sin(45deg)/2.419 = 0.7071/2.419 = 0.2923

therefore angle RSN = 16.9964 degrees, which is called angle X. later he writes that 4 alpha = 180-16.9964 = 163.0036 so alpha, the pavilion angle, is 40.7509 degrees.

In summary, for RI 2.417 the pavilion angle should be 40.74 degrees and for RI 2.419 it should be 40.75 degrees.

A nice illustration of one of the material properties which causes EighStar to have to make small adjustments for every diamond they cut in the process of achieving their unique result.

(edited to move some brackets into the right places)

[Edited by Jamesd on 05-24-01 at 09:58 AM]

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Quote this post and reply to it Post#2 @ 05-19-01 , 09:02 PM


Gee James you really know how to put some snooze in the Schmooze
Just kidding, I read some of that.

If you where in retail this would put the baby to sleep and he would never get his new shoes

Brad

[Edited by Brad on 05-19-01 at 09:06 PM]


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Quote this post and reply to it Post#3 @ 05-19-01 , 09:26 PM


Was this guy a genius or what? All these years later and he`s still reviewed.


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Quote this post and reply to it Post#4 @ 05-19-01 , 09:31 PM


Anyone have a Photo? Kinda like the Einstein one ?


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Quote this post and reply to it Post#5 @ 05-19-01 , 09:34 PM


Quote:
In summary, for RI 2.417 the pavilion angle should be 40.74 degrees and for RI 2.419 it should be 40.75 degrees.


So now the question is: do cutters have the equipment to measure and control the angles down to 0.01?? If not, they will be hard pressed to compensate for changes in RI by making such infinitesimal changes to the angles.

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Quote this post and reply to it Post#6 @ 05-19-01 , 09:42 PM


Hopefully a cutter will comment but I think the answer is no, the usual equipment is calibrated in degrees. Some of the fancier machine cutting tools might well have the capability to do odd parts of angles, particularly if based on normal computerised machining tools.

Even with fixed settings I expect that a cutter can tweak the angles by hand to achieve a particular result.

I've no idea at all what tolerances in settings the super-ideal cutters are using and how they fine tune their cuts.

Brad,

Nothing wrong with putting babies to sleep.

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Quote this post and reply to it Post#7 @ 05-19-01 , 09:46 PM


Quote:
Originally posted by Johnny Boy
Quote:
In summary, for RI 2.417 the pavilion angle should be 40.74 degrees and for RI 2.419 it should be 40.75 degrees.


So now the question is: do cutters have the equipment to measure and control the angles down to 0.01?? If not, they will be hard pressed to compensate for changes in RI by making such infinitesimal changes to the angles.



Man we are talking the freckle on a Knats behind, maybe smaller If a cutter really wanted to drive himself up the wall



Brad



[Edited by Brad on 05-19-01 at 09:52 PM]


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Quote this post and reply to it Post#8 @ 05-19-01 , 10:10 PM


Quote:
Nothing wrong with putting babies to sleep.


Tell me about it!

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Quote this post and reply to it Post#9 @ 05-19-01 , 10:17 PM


Quote:
Even with fixed settings I expect that a cutter can tweak the angles by hand to achieve a particular result.

I've no idea at all what tolerances in settings the super-ideal cutters are using and how they fine tune their cuts.


If we look at the Megascope or advanced Sarin results (which report the individual angles rather than just the average), even the super-ideals can vary by 0.2-0.5. The deviations reported are in increments of 0.1 (10x more than 0.01) although perhaps this may be more a machine limitation, i.e. getting to the limits of the machines sensitivity.

I don't discount the possibility of the cutter's eye and hand being finer... I suppose that's where the art and skill comes in.

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Quote this post and reply to it Post#10 @ 05-19-01 , 10:19 PM


Hows the new one doing anyway Bedtime stories with Marcel



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Quote this post and reply to it Post#11 @ 05-19-01 , 10:42 PM


JB;
Your line of...
"even the super-ideals can vary by
.02-.05.."

I'm quite sure you mean that as a compliment to us in the diamond-cutting
fraternity!

Barry
http://www.superbcert.com

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Quote this post and reply to it Post#12 @ 05-19-01 , 10:48 PM


Hows production Barry. Anything new come off that wheel in the last six months ?


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Quote this post and reply to it Post#13 @ 05-20-01 , 12:20 AM


Brad...

Evan is well. Getting naughtier by the day.

barry...

Yes, that was meant as a compliment!

Now that you're here, can you tell us how finely tuned are the eyes and hands of your cutters? Are they able to make such tiny adjustments to facet angles to compensate for RI variations? Or do you think this issue about RI variations is irrelevant? Goodness knows we've had enough discussion about it, without any firm conclusion.

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Quote this post and reply to it Post#14 @ 05-20-01 , 12:38 AM


JB;

1. Thank you.

2. The very minute RI differentials
under discussion, are I believe,
insignificant, and not a major factor
in the final "L@@K" and
quantitative out-put.

We use specially engineered guages
that have been intially calibrated to a set of "master stones".

In the cutting process itself,
Crown and Pavilion facets are
measured and re-measured.
Grain lines, knots, and placement of
imperfections are just some of the
constant problems being confronted
in the faceting and polishing.

Barry
[url]http://www.superbcert.com[/url


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Quote this post and reply to it Post#15 @ 05-20-01 , 01:59 AM


Hi JamesD,

Thank you!!

You helped me and few others a lot. I must admit I did not follow all the maths behind you summary but I am sure your calculations are ok.
0.01 degree!! And thats MAX!

I knew it would be small.

S



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Quote this post and reply to it Post#16 @ 05-20-01 , 02:06 AM


Jhonny boy,

A new fairy tail to your kid.

Gabi Tolkowsky talking R.I. changes in diamonds to Rockdoc

S

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Quote this post and reply to it Post#17 @ 05-20-01 , 02:12 AM


Barry,
thank you.
That was frank talk.

Grain lines, knots and imperfections. This is much more understandable.


Can you tell us something about the grain lines?

Is problem with grain lines a polish problem or do they cause irregular bending to the path of the light inside a stone?

S

[Edited by Sibelius on 05-20-01 at 02:13 AM]

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Quote this post and reply to it Post#18 @ 05-20-01 , 06:21 AM


S...

Yeah, he's gonna grow up to be a diamond kid!

barry...

Thanks for your views.

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Quote this post and reply to it Post#19 @ 05-20-01 , 07:44 AM


Sibelius;

1. Can definitely be a problem
for polish and symmetry.

2. Consequently will have
an effect on directional light output
that can possibly be measured by the BrillianceScope.

Barry
http://www.superbcert.com







[Edited by barry on 05-20-01 at 10:44 AM]

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Quote this post and reply to it Post#20 @ 05-20-01 , 12:03 PM


Barry how many cutters do you have in your factory ? Or do you cut them all yourself while entertaining on diamondtalk ? Also how do cutters stay employed when there is nothing coming out of production ?


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Quote this post and reply to it Post#21 @ 05-20-01 , 05:12 PM


Brad

Why did you stop carrying Barry's stones?

R/A

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Quote this post and reply to it Post#22 @ 05-21-01 , 07:39 PM


Hi Rank I won`t ignore your question After a bunch of nonsense it was time to disconnect.

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Quote this post and reply to it Post#23 @ 05-21-01 , 10:50 PM


Was it the Jonathan deal?

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Quote this post and reply to it Post#24 @ 05-22-01 , 01:10 PM


Hi Rank,
It wasn't so much Jonathan as it was the man behind the product. There are many reasons.


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Quote this post and reply to it Post#25 @ 05-23-01 , 05:58 PM


I have been involved with precision machinery and gaging much of my life, and I also cut stones. I think it unrealistic to consider control of angles within 0.01 and the surfaces are too small to measure the angles to this degree of accuracy.

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