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62 % table- good crown and pav angles are....Rhino?

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iwannaprettyone

iwannaprettyone

Ideal_Rock
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Feb 5, 2002
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I found this article from 2003 and Rhino says:

"Tables can be up around the 60-62% range IF YOU''VE GOT THE PROPER crown/pavilion angles. The sad fact is that most of the time those larger tables are coupled with nasty crown/pavilion angles."

What would these angles potentially be?
 
Use the HCA tool and type in 60% table. You''ll get a pretty good idea of the angles.
 
Date: 8/2/2007 3:53:34 PM
Author: whatmeworry
Use the HCA tool and type in 60% table. You''ll get a pretty good idea of the angles.
Click to expand...
ditto, but I should add that many like me still don''t prefer stones with tables this large. They lack fire and have a huge table glare that is distracting. However, many do like the appearance and they offer a nice spread often if you are one of the people that like this look.
 
40.9-41/32-33-34
 
At these table sizes you'll find good performance with near-Tolk pavilion angles coupled with crowns a bit shallower than near-Tolk (appx 32.5–34.5).As PA goes up CA goes down, so 41/33 can be nice.So can 40.6/34.5. As kcoursolle mentioned, this is a different look - though not necessarily less appealing.

Per the AGS cut guides, there are equal opportunities for PA 40.6-41.0 in common sizes (6mm-8mm) and that’s in agreement with the appealing 60/60s I see. There is a nearby jeweler who primarily sells these makes and sometimes we play doctor.
1.gif


(reproduced with permission)

AGSL_60T_Guides.jpg
 
Date: 8/2/2007 4:23:31 PM
Author: JohnQuixote

At these table sizes you''ll find good performance with near-Tolk pavilion angles coupled with crowns a bit shallower than near-Tolk (appx 32.5–34.5).As PA goes up CA goes down, so 41/33 can be nice.So can 40.6/34.5. As kcoursolle mentioned, this is a different look - though not necessarily less appealing.

Per the AGS cut guides, there are equal opportunities for PA 40.6-41.0 in common sizes (6mm-8mm) and that’s in agreement with the appealing 60/60s I see. There is a nearby jeweler who primarily sells these makes and sometimes we play doctor.
1.gif


(reproduced with permission)
Click to expand...
So if the table size increases the crown height will get steeper?
 
Date: 8/2/2007 4:32:42 PM
Author: iwannaprettyone


Date: 8/2/2007 4:23:31 PM
Author: JohnQuixote



At these table sizes you'll find good performance with near-Tolk pavilion angles coupled with crowns a bit shallower than near-Tolk (appx 32.5–34.5).As PA goes up CA goes down, so 41/33 can be nice.So can 40.6/34.5. As kcoursolle mentioned, this is a different look - though not necessarily less appealing.

Per the AGS cut guides, there are equal opportunities for PA 40.6-41.0 in common sizes (6mm-8mm) and that’s in agreement with the appealing 60/60s I see. There is a nearby jeweler who primarily sells these makes and sometimes we play doctor.
1.gif


(reproduced with permission)
Click to expand...
So if the table size increases the crown height will get steeper?
Click to expand...
Actually, if crown angle is the same for 2 round brilliants the crown height decreases as table size increases.

Think of the crown like a mountain. If you polish a small 'table' onto the top of that mountain you reduce its height a bit. If you polish down even more to make the table larger the angle of the mountain remains the same but its height is reduced.

So, it makes sense that as table size increases the crown angles most appropriate for the diamond get a bit more shallow if you want to maintain a good performance relationship.
 
An the effect of a bigger table is primarily glare and spread? Or is this a big assumption on my part?
33.gif
 
Date: 8/2/2007 4:57:24 PM
Author: iwannaprettyone
An the effect of a bigger table is primarily glare and spread? Or is this a big assumption on my part?
33.gif
Click to expand...
also white/bright look rather than colored fire look.
 
Date: 8/2/2007 4:57:24 PM
Author: iwannaprettyone
An the effect of a bigger table is primarily glare and spread? Or is this a big assumption on my part?
33.gif
Click to expand...
Assumption. 60-62 can be very beautiful.

Greetings iwannaprettyone,

Thanks for your question. I didn''t realize there were so many other Rhino''s around here.
41.gif

When determining which proportion sets will look best with tables of this size and not having the diamonds in hand it depends on which pavilion angle you''re going to couple with the crown as mentioned. With a 60% table and using say a 40.8 pavilion angle it appears you can go up to almost 36 degrees and maintain a nice bright, fiery stone. Below is a graphic for such a stone assuming precise optical symmetry. Larger tables do not always equate to better spread although they''ll produce slightly more glare from reflected light off the table. They can and are very fiery too when cut right.


This comparison is of a 40.8 pavilion angle coupled with a 35.8 crown angle alongside a 41 degree pavilion angle coupled with a 35 degree crown angle. If anyone wants a gem advisor file let me know and I can generate it for ya.


Peace,





60tablecompare.gif
 
And for a comparison here is the 35/41 combo alongside a 35.8/41 combo.

Here you can begin to see the ill effects of leakage under the table which would exist in the 35.8/41 combo.

60tablecompare2.gif
 
What about shallower crown and deeper pav?

Strmdr has explained to me about the relationship being linear and I know that pav angle changes have more impact than crown changes.
 
Date: 8/2/2007 6:36:33 PM
Author: iwannaprettyone
What about shallower crown and deeper pav?

Strmdr has explained to me about the relationship being linear and I know that pav angle changes have more impact than crown changes.
Click to expand...
Correct.

If we dropped the pavilion angle to a 41.4 angle I''d at least want to see a 33.5 crown or a 32.5. Here''s a graphic of both side by side.

Mind you I wouldn''t drop bucks on anything until I was able to perform an actual inspection of course. Have you downloaded the Gem Advisor program iwapo?

Kind regards,

t60p414compare.gif
 
one thing too keep in mind is that lgf% is going to make a larger difference once you get out there in the over 41 degree range with 60% tables as is optical symmetry and tightness.
With average cutting I would be very hesitant too go there and is anyone actually cutting them with any precision?
 
Date: 8/2/2007 7:14:05 PM
Author: strmrdr
one thing too keep in mind is that lgf% is going to make a larger difference once you get out there in the over 41 degree range with 60% tables as is optical symmetry and tightness.
With average cutting I would be very hesitant too go there and is anyone actually cutting them with any precision?
Click to expand...
Hence my comment... "Mind you I wouldn't drop bucks on anything until I was able to perform an actual inspection of course."
 
No Rhino I haven''t downloaded gemadviser...is it a free download?

By "at least 33.5" do you mean 33.5 plus or minus...so between 34.5 and 35 would be disasterous? I think I am still a little confused (geometry was never my strong point even though advanced calc was cake).
33.gif
 
Iv been playing with DC and when it comes too light return a
41/33/60t/80lgf is a tolk clone with a different personality.
The average for light return stereo came out too 1.00 but it comes from different areas and face up it is brighter than tolk falling a little behind when tilted.
That combo is shown on the charts above as an AGS0 where it properly belongs.
 
Do you have a gemadvisor file available for the 41/33/60t? I downloaded the reader this morning.
 
Date: 8/2/2007 11:35:21 PM
Author: iwannaprettyone
No Rhino I haven''t downloaded gemadviser...is it a free download?

By ''at least 33.5'' do you mean 33.5 plus or minus...so between 34.5 and 35 would be disasterous? I think I am still a little confused (geometry was never my strong point even though advanced calc was cake).
33.gif
Click to expand...
Good mornign iwapo.
35.gif


Yep, its a free download you can get here.
http://www.octonus.com/download/GemAdviserSetup.exe

You install the program, run it once then any .gem file you open (here or on our site) will automatically open the file in that program and there''s a bit of good information you can garner from it.

In answer to your question. 33.5 minus. If you couple a 34.5/41.4 cr/pav combo with a 60 table you get what''s in the graphic below. There are most definitely worse combos out there but this would have a little too much leakage for my personal likings although it would still qualify as a GIA Ex (as long as all other factors met their conditions, ie weight ratio, polish/symmetry etc).

Do you know the proportions of the stone with the 60-62 table you''re inquiring about? Perhaps I can make you a model to give you a rough idea?

Kind regards,

t60cr345p414.gif
 
Date: 8/3/2007 12:49:23 AM
Author: strmrdr
Iv been playing with DC and when it comes too light return a
41/33/60t/80lgf is a tolk clone with a different personality.
The average for light return stereo came out too 1.00 but it comes from different areas and face up it is brighter than tolk falling a little behind when tilted.
That combo is shown on the charts above as an AGS0 where it properly belongs.
Click to expand...
I''d like to see how that actually looks with 60 stars. In DC do you use length or depth on the LG''s?
 
Date: 8/3/2007 11:30:47 AM
Author: iwannaprettyone
Do you have a gemadvisor file available for the 41/33/60t? I downloaded the reader this morning.
Click to expand...

Here ya go.
 

Attachments

My studs each have 33 degree pavilions and tables of 60-61%. They scored 1.7 and 2.0 on the HCA, and they are beautiful in my humble opinion. They each had depths under 60%, and this allowed me to get 0.72ctw that looks like at least 0.75ctw. I don''t know that I''d have strayed so far from the "ideal" for an engagement ring diamond, but when I found this set it just seemed like such a cool combination and good deal that I couldn''t pass it up.
 
Date: 8/3/2007 12:49:23 AM
Author: strmrdr
Iv been playing with DC and when it comes too light return a
41/33/60t/80lgf is a tolk clone with a different personality.
The average for light return stereo came out too 1.00 but it comes from different areas and face up it is brighter than tolk falling a little behind when tilted.
That combo is shown on the charts above as an AGS0 where it properly belongs.
Click to expand...
strm, try throwing a 35 crown onto that combo and look at what happens to the appearance in office lighting.
 
My apologies iwapo, when another vendors stones get involved I can''t personally comment.
5.gif
 
ok. I understand.

Can I see the one that strmr is playing with??
 
Date: 8/3/2007 12:07:09 PM
Author: iwannaprettyone
ok. I understand.

Can I see the one that strmr is playing with??
Click to expand...
Yep, If you look at my post above you''ll see the .gem file underneath and in the bottom right corner of the post. It has a little paper clip alongside the attachment. Attached to this post is the same specs with a 35 crown if you want to compare the suggestion I made to strm in the office light view.
 

Attachments

Date: 8/3/2007 11:52:43 AM
Author: Rhino

Date: 8/3/2007 11:30:47 AM
Author: iwannaprettyone
Do you have a gemadvisor file available for the 41/33/60t? I downloaded the reader this morning.
Click to expand...

Here ya go.
Click to expand...

Very cool! Thanks...I love new toys!
 
Strmr- what are your observations?
 
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