Please explain this OECs darkness to me

[mela lu]

Can someone teach me why this OEC has a big black blob in the center rather than nice facet patterns? Is this due to light leakage (too deep a cut?) What causes this unattractive look in the center vs some of the beautiful bright and colorful patterns we see here in OECs?

Thanks for the tutorial

I''m training my OEC eye....

 

[diagem]

Date: 6/30/2007 10:06:21 AM
Author:mela lu
Can someone teach me why this OEC has a big black blob in the center rather than nice facet patterns? Is this due to light leakage (too deep a cut?) What causes this unattractive look in the center vs some of the beautiful bright and colorful patterns we see here in OECs?

Thanks for the tutorial

I''m training my OEC eye....

Could be ''just'' a bad shot...

 

[mela lu]

yes...you''re right, it could be! ...I''m heading offline now, but will catch up in a bit. Thanks to all in advance for their theories!

 

[prelude4]

err...abit off topic..but wat is OEC?

 

[diagem]

Date: 6/30/2007 10:18:57 AM
Author: prelude4
err...abit off topic..but wat is OEC?

Old European Cut...., was cut in between the Antique Cushion called Old-Mine Brilliant/Cut and the modern Round Brilliant....

 

[prelude4]

Date: 6/30/2007 10:22:50 AM
Author: DiaGem

Date: 6/30/2007 10:18:57 AM
Author: prelude4
err...abit off topic..but wat is OEC?

Old European Cut...., was cut in between the Antique Cushion called Old-Mine Brilliant/Cut and the modern Round Brilliant....

thank you.

 

[Cehrabehra]

Date: 6/30/2007 10:06:21 AM
Author:mela lu
Can someone teach me why this OEC has a big black blob in the center rather than nice facet patterns? Is this due to light leakage (too deep a cut?) What causes this unattractive look in the center vs some of the beautiful bright and colorful patterns we see here in OECs?

Thanks for the tutorial

I''m training my OEC eye....

Usually you see a cross - a maltese cross I think it is called - and not have all 8 facets reflecting the same thing... doesn''t mean IMO that the stone is ugly - just means that it will be reflecting a lot of what it *sees*. I think fair people have perhaps an advantage with stones like this.

 

[junior35]

Date: 6/30/2007 10:06:21 AM
Author:mela lu
Can someone teach me why this OEC has a big black blob in the center rather than nice facet patterns? Is this due to light leakage (too deep a cut?) What causes this unattractive look in the center vs some of the beautiful bright and colorful patterns we see here in OECs?

Thanks for the tutorial

I''m training my OEC eye....

You''re on the right track.The stone is too deep on the pavillion side,so what you see is the reflection of the setting and not of the table.
It has its charm.

 

[AdaBeta27]

May be a "nail" or "nail head" (dark center) diamond from a steep crown angle + a steep / deep pavillion? See chart:
http://www.gemology.ru/cut/english/comp/kozibe.html
Nail and fisheye pic at bottom right, here:
http://www.gemsociety.org/info/igem21.htm

I suppose it could also be a shallower "head shadow" diamond that has a dark center when viewed close up. Remount it in prong setting.

Either way, it could probably be made more attractive by:
1. Try clean and polish the inside of the setting that's reflecting in the stone. Old platinum for certain and maybe old palladium tends to darken (almost blacken) and starts looking like steel or such after many years.
2. If that doesn't help, re-mount in prongs so that light gets in. Avoid any setting that has an enclosed boxy head.

 

[mela lu]

Date: 6/30/2007 11:46:10 AM
Author: Cehrabehra
Usually you see a cross - a maltese cross I think it is called - and not have all 8 facets reflecting the same thing... doesn''t mean IMO that the stone is ugly - just means that it will be reflecting a lot of what it *sees*. I think fair people have perhaps an advantage with stones like this.

Cehra...can you expand on what you mean by "fair people have perhaps an advantage..." I don''t think i know what that expression means.

Thanks!

 

[diagem]

Date: 6/30/2007 5:50:07 PM
Author: junior35

Date: 6/30/2007 10:06:21 AM
Author:mela lu
Can someone teach me why this OEC has a big black blob in the center rather than nice facet patterns? Is this due to light leakage (too deep a cut?) What causes this unattractive look in the center vs some of the beautiful bright and colorful patterns we see here in OECs?

Thanks for the tutorial

I''m training my OEC eye....

You''re on the right track.The stone is too deep on the pavillion side,so what you see is the reflection of the setting and not of the table.
It has its charm.

J, can you explain this statement better?

 

[Kaleigh]

Date: 7/1/2007 1:12:25 AM
Author: DiaGem

Date: 6/30/2007 5:50:07 PM
Author: junior35

Date: 6/30/2007 10:06:21 AM
Author:mela lu
Can someone teach me why this OEC has a big black blob in the center rather than nice facet patterns? Is this due to light leakage (too deep a cut?) What causes this unattractive look in the center vs some of the beautiful bright and colorful patterns we see here in OECs?

Thanks for the tutorial

I''m training my OEC eye....

You''re on the right track.The stone is too deep on the pavillion side,so what you see is the reflection of the setting and not of the table.
It has its charm.

J, can you explain this statement better?

Yes please...

 

[junior35]

In simplified layman terms,if the angle on the pavillion is too deep,instead of getting a reflection of the table and star facets,you will actually get a reflection of the opposite pavillion facets. Light goes in ,but doesn't check out.
Look at this link and see the diagram for deep stones. http://www.ejeweler.com/Cut.html
This is quite common in OEC as these stones were cut with the intention to retain as much weight as possible from the rough.This means going deeper on the bottom and higher on the top.

 

[strmrdr]

too deep pavilion.....

 

[Garry H (Cut Nut)]

We must be careful not to create missinformation.
This diamond does not have a see through effect within the table, because as storm says - it is cut too deeply.

The effect is called a ''nail head'' because, like a nail head, it reflects the light straight back to the observer, and unless you as an observer have a very bright face, you will see relative darkness. In this case we see the very dark camera lens.

This is a ray trace for a 45 degree pavilion old mine cut.
Any diamond with a 44 to 45 degree plus pavilion will look dark in the center. Unfortunately many gem teachers and institutes did not know much about this until recently, so there is a lot of misinformation. There are even lots of diamond cut tutorials that show ray traces like this to indicate that the diamond has ''ideal cut''.

 

[Garry H (Cut Nut)]

Date: 7/3/2007 12:44:28 AM
Author: junior35
In simplified layman terms,if the angle on the pavillion is too deep,instead of getting a reflection of the table and star facets,you will actually get a reflection of the opposite pavillion facets. Light goes in ,but doesn''t check out.
Look at this link and see the diagram for deep stones. http://www.ejeweler.com/Cut.html
This is quite common in OEC as these stones were cut with the intention to retain as much weight as possible from the rough.This means going deeper on the bottom and higher on the top.

The information on that site is very wrong in this case Junior.
For the light entering the table to leak out as they have shown the pavilion needs to be around 53 degrees or 66% pavilion depth. A cutter would never do this because they could turn the stone and get a better yeild, aside from the fact that no one would buy the stone.
The total depth of such a stone would be over 80%.

The shallow example is also almost impossible - the pavilion angle must be less than 24.5 degrees or <23%.

So as examples of good and bad cut, these simple sketches are quite silly.

 

[junior35]

Date: 7/3/2007 1:53:14 AM
Author: Garry H (Cut Nut)

Date: 7/3/2007 12:44:28 AM
Author: junior35
In simplified layman terms,if the angle on the pavillion is too deep,instead of getting a reflection of the table and star facets,you will actually get a reflection of the opposite pavillion facets. Light goes in ,but doesn''t check out.
Look at this link and see the diagram for deep stones. http://www.ejeweler.com/Cut.html
This is quite common in OEC as these stones were cut with the intention to retain as much weight as possible from the rough.This means going deeper on the bottom and higher on the top.

The information on that site is very wrong in this case Junior.
For the light entering the table to leak out as they have shown the pavilion needs to be around 53 degrees or 66% pavilion depth. A cutter would never do this because they could turn the stone and get a better yeild, aside from the fact that no one would buy the stone.
The total depth of such a stone would be over 80%.

The shallow example is also almost impossible - the pavilion angle must be less than 24.5 degrees or <23%.

So as examples of good and bad cut, these simple sketches are quite silly.

You are right.The example is not great,I would have loved to post the simulated result as strmrdr did,but I was just trying to find a simplified diagram with an associated photo of a "nail head" for illustrational purposes only.

 

[mela lu]

Great mini-lesson. Thanks Garry! Just to clarify - this is not my ring...but one I found online and wondered about it''s dark face.
Here is a profile of it. You can see the deep pavillion.

 

[He Scores]

A dark center''d diamond is a result of the bottom pavillion angle exceeding 40.75 degrees. The higher the angle the greater the dark center.

Bill Bray
Diamond Cutter

 

[mela lu]

So let''s just say that whoever owned these stones wanted to improve the light preformance...could they have the pavillion re-cut to a more appropriate pavilion angle? Or is that a no-no?

*egads*

 

[strmrdr]

Date: 7/3/2007 11:05:34 AM
Author: mela lu
So let''s just say that whoever owned these stones wanted to improve the light preformance...could they have the pavillion re-cut to a more appropriate pavilion angle? Or is that a no-no?

*egads*

more than likely it would be recut into a RB if it was recut.

 

[strmrdr]

Thats even worse than what I modeled...bleck!

 

[strmrdr]

Date: 7/3/2007 9:26:57 AM
Author: junior35
You are right.The example is not great,I would have loved to post the simulated result as strmrdr did,but I was just trying to find a simplified diagram with an associated photo of a ''nail head'' for illustrational purposes only.

http://www.octonus.com/oct/products/3dcalc/standard/
DiamCalc is a diamond nuts best friend.

 

[mela lu]

Nail.head.

final answer.

 

[He Scores]

Date: 7/3/2007 11:05:34 AM
Author: mela lu
So let''s just say that whoever owned these stones wanted to improve the light preformance...could they have the pavillion re-cut to a more appropriate pavilion angle? Or is that a no-no?

*egads*

The stone could be cut to improve the performance whether the final shape is to retain a cushion or have it re-cut into a modern.

Bill Bray
Diamond Cutter