What do you find is the most confusing about diamond cut?

[strmrdr]

If there is a trend towards one area of confusion I will post a thread on the topic over the next couple days for the FAQ.
Otherwise I may just address a few of them.

What do you find most confusing in the diamond cut discussions?

 

[pyramid]

I would like to know more about how LGF% works - is it in relation to crown angle, if it is not too complicated to explain it all.

 

[pyramid]

I mean I know LGF% is percentage of Lower Girdle Facet to Pavillion Depth. I know that longer facets give more Pinpoint Scintillation. In a post the other day about a FIC you were mentioning it in relation to crown angle for that particular type of search and I wondered how you worked that out?

 

[kcoursolle]

Date: 2/29/2008 11:50:06 AM
Author: Pyramid
I would like to know more about how LGF% works - is it in relation to crown angle, if it is not too complicated to explain it all.

ditto, this isn''t something I still don''t understand well too!

 

[diagem]

Date: 2/29/2008 12:07:26 PM
Author: Pyramid
I mean I know LGF% is percentage of Lower Girdle Facet to main Pavillion facet lenght (Depth). I know that longer facets give more Pinpoint Scintillation. In a post the other day about a FIC you were mentioning it in relation to crown angle for that particular type of search and I wondered how you worked that out?

 

[diagem]

Date: 2/29/2008 11:26:00 AM
Author:strmrdr
If there is a trend towards one area of confusion I will post a thread on the topic over the next couple days for the FAQ.
Otherwise I may just address a few of them.

What do you find most confusing in the diamond cut discussions?

Just thought of something...
If it was not done before..., I think it might be a good idea to take the various high-technologies used here on PS to educate the consumer and use it for a presentation on the ABC''s of the way Diamonds are genuinely and practically cut! And I mean the whole path! From the various rough shapes cutters chose to start with to the last half facet or Lower Girdle Facet (lgf) which is polished on.

The technology is available..., why not use it to envision the whole cutting process!


storm???

 

[strmrdr]

Date: 2/29/2008 3:35:00 PM
Author: DiaGem

Date: 2/29/2008 11:26:00 AM
Author:strmrdr
If there is a trend towards one area of confusion I will post a thread on the topic over the next couple days for the FAQ.
Otherwise I may just address a few of them.

What do you find most confusing in the diamond cut discussions?

Just thought of something...
If it was not done before..., I think it might be a good idea to take the various high-technologies used here on PS to educate the consumer and use it for a presentation on the ABC''s of the way Diamonds are genuinely and practically cut! And I mean the whole path! From the various rough shapes cutters chose to start with to the last half facet or Lower Girdle Facet (lgf) which is polished on.

The technology is available..., why not use it to envision the whole cutting process!


storm???

that would be way kewl, but I''m not sure I could pull it off and it would take a long time.
While I have a general understanding of the cutting process I''m weak on why given a particular piece of rough a cutter would pick a specific shape to cut it into.
That is one part of the process that is still behind the curtain and because of fraudulent rough scams discussing rough diamonds is against the rules here in most cases. (yield discussions for a specific cut and cutting technology would be OK)
I think it could be done within the spirit of the rules but would need admin approval.

 

[strmrdr]

lgf% is a hotly debated subject but I will look into it and think about how too go about it without getting into a fight.

Keep the ideas coming!! :}

 

[Missrocks]

Ditto on the LGF%. That would be great.
Also, I would like to understand idealscope images better. For example I''ve seen fatter arrows vs. skinny arrows. I was told the difference was the created by the contrast between lower girdle facets and pavilion mains..Is this correct? I was also told that skinnier was better, but was not told why. Any elaboration on this would be great. Also, some stones tend to show darker, more pronounced arrows in idealscope images. Can I assume maybe this is from a more distinct H&A pattern? Forgive me if this was covered before, but I have yet run across it and was just curious.

 

[Garry H (Cut Nut)]

Date: 2/29/2008 11:48:55 PM
Author: Missrocks
Ditto on the LGF%. That would be great.
Also, I would like to understand idealscope images better. For example I''ve seen fatter arrows vs. skinny arrows. I was told the difference was the created by the contrast between lower girdle facets and pavilion mains..Is this correct? I was also told that skinnier was better, but was not told why. Any elaboration on this would be great. Also, some stones tend to show darker, more pronounced arrows in idealscope images. Can I assume maybe this is from a more distinct H&A pattern? Forgive me if this was covered before, but I have yet run across it and was just curious.

Shallower stones show darker star patterns thru the Ideal-scope, and brighter star patterns when you slightly tilt the stone when you have a big light just over your head (eg fluoro)

as the stone gets to step deep - say GIA EX of 41.2Pav 35 crown and beyond the star and the bright flash gets slightly weaker.

As the stone gets shallower the darkness of the star becomes more apparent and you need to tilt the stone more to see the light above your head.
As the stone gets steep deep you loose light return in the area just inside the table

 

[coatimundi_org]

Date: 3/1/2008 1:24:27 AM
Author: Garry H (Cut Nut)

Date: 2/29/2008 11:48:55 PM

Author: Missrocks

Ditto on the LGF%. That would be great.

Also, I would like to understand idealscope images better. For example I've seen fatter arrows vs. skinny arrows. I was told the difference was the created by the contrast between lower girdle facets and pavilion mains..Is this correct? I was also told that skinnier was better, but was not told why. Any elaboration on this would be great. Also, some stones tend to show darker, more pronounced arrows in idealscope images. Can I assume maybe this is from a more distinct H&A pattern? Forgive me if this was covered before, but I have yet run across it and was just curious.

Shallower stones show darker star patterns thru the Ideal-scope, and brighter star patterns when you slightly tilt the stone when you have a big light just over your head (eg fluoro)


as the stone gets to step deep - say GIA EX of 41.2Pav 35 crown and beyond the star and the bright flash gets slightly weaker.


As the stone gets shallower the darkness of the star becomes more apparent and you need to tilt the stone more to see the light above your head.

As the stone gets steep deep you loose light return in the area just inside the table

Garry,

Missrocks mentioned skinnier arrows. My stone has these skinny arrows. Can you explain why? or what it means?
Thanks!

eta: sorry, if you've already explained it in your above post. I don't understand.

 

[strmrdr]

Date: 3/1/2008 1:31:02 AM
Author: coatimundi


Garry,

Missrocks mentioned skinnier arrows. My stone has these skinny arrows. Can you explain why? or what it means?
Thanks!

eta: sorry, if you''ve already explained it in your above post. I don''t understand.

I''m not Garry but it means it has longer lower girdle facets. ie: higher lgf%
I will cover what it means when I do the thread on them.

 

[coatimundi_org]

Thanks Strmrdr!
Will look out for your thread.

 

[strmrdr]

image borrowed from a post from a long time ago.

 

[diagem]

Date: 3/1/2008 2:02:46 AM
Author: strmrdr

image borrowed from a post from a long time ago.

Storm..., can you show these examples with a culet-up image...., or a close-up profile?

 

[strmrdr]

Date: 3/1/2008 2:11:27 AM
Author: DiaGem
Storm..., can you show these examples with a culet-up image...., or a close-up profile?

good idea I will include that in my thread on lgf%.

 

[coatimundi_org]

In general with the disclaimer above firmly in mind:
70% - Fire over light return, broadest flashes,arrows pop under a wide range of light conditions, can make the diamond look dark.

75% - Fire over light return, broad flashes,arrows pop under a wide range of light conditions.

77%-82% Well balanced between fire and white light return. With a huge arguement over which is better. Most of the premium stones prefered by pricescope dealers are in this range.

85% - white light over fire, poor contrast.

Strmrdr, I dug up this quote of yours.
From the chart above, my stone falls between the 80 and 85--just visually going by the size of the arrows. (and I'm thinking it's closer to 80 because it exhibits so much fire--just going from your notes) How would I get the real measurement? Is there an equation?

Also, I've been meaning to ask this too: Is there an equation for crown and pavillion angles for those of us who have certs that don't give that info? I've looked this up, and everything I've read says no, but this is something that confuses me. If I have all the measurements in mm, shouldn't I be able to plug them into some simple mathematical equation?

Thanks!

 

[strmrdr]

Date: 3/1/2008 2:35:08 AM
Author: coatimundi


Strmrdr, I dug up this quote of yours.
From the chart above, my stone falls between the 80 and 85--just visually going by the size of the arrows. How would I get the real measurement? Is there an equation?

Also, I''ve been meaning to ask this too: Is there an equation for crown and pavillion angles for those of us who have certs that don''t give that info? I''ve looked this up, and everything I''ve read says no, but this is something that confuses me. If I have all the measurements in mm, shouldn''t I be able to plug them into some simple mathematical equation?
Thanks!

I have learned a lot since that quote as has the everyone else.
There is no equation visual eval is as close as your going too get without a sarin/ogi/helium scan.
There are some tricks with DiamCalc and IS images that can get close too but its problematic.
No there isn''t one for the angles either.

 

[coatimundi_org]

Thanks for the reply Strmrdr!

 

[strmrdr]

Date: 3/1/2008 2:44:57 AM
Author: coatimundi
Thanks for the reply Strmrdr!

welcome, thanks it gives me ideas on what I need too cover.

 

[Garry H (Cut Nut)]

Skinnier arrows mean
1. longer lower girdle facets
2. larger table size

longer tend to have a little less fire and a little more light return / brightness - its a trade off

 

[Missrocks]

Thanks Strmrdr and Garry for all the info!


One more question...The first time I saw the fatter vs. skinnier the two diamonds being compared had exact angle combo. Same 80 lgf%, 40.8 pavilion, and I can't remember the crown angle other than both were the same on both, tables were 56 % and 57 %. One diamond was .14 pts bigger in size than the other. The smaller one had fatter arrows and the larger had skinnier, very distinctly different. Is there another reason that causes the arrows to differ?

 

[lisa1.01fvs1]

Ok, I apologize in advance for offending you outrageously knowledgeable folks but.....

When I stare at the center of the stone, sometimes I see a small circular bright area at the bottom.

Guessing this is the culet area?

However, I can''t quite get a complete circle visually (half circle, maybe 3/4). Never a complete circle.

What is this? Cut, light magic, hallucination?

Just wondering

 

[diagem]

Date: 3/1/2008 12:58:23 PM
Author: Missrocks
Thanks Strmrdr and Garry for all the info!


One more question...The first time I saw the fatter vs. skinnier the two diamonds being compared had exact angle combo. Same 80 lgf%, 40.8 pavilion, and I can''t remember the crown angle other than both were the same on both, tables were 56 % and 57 %. One diamond was .14 pts bigger in size than the other. The smaller one had fatter arrows and the larger had skinnier, very distinctly different. Is there another reason that causes the arrows to differ?

Differ in size or appearance?

 

[strmrdr]

Date: 3/1/2008 12:58:23 PM
Author: Missrocks
Thanks Strmrdr and Garry for all the info!


One more question...The first time I saw the fatter vs. skinnier the two diamonds being compared had exact angle combo. Same 80 lgf%, 40.8 pavilion, and I can''t remember the crown angle other than both were the same on both, tables were 56 % and 57 %. One diamond was .14 pts bigger in size than the other. The smaller one had fatter arrows and the larger had skinnier, very distinctly different. Is there another reason that causes the arrows to differ?

let me guess the 80% was off a GIA report?
GIA rounds too the nearest 5 so 80 can be from 77.51 too 82.49 and there is a visible difference in the size of the arrows in that range.

 

[Missrocks]

Date: 3/1/2008 2:06:50 PM
Author: DiaGem

Date: 3/1/2008 12:58:23 PM
Author: Missrocks
Thanks Strmrdr and Garry for all the info!


One more question...The first time I saw the fatter vs. skinnier the two diamonds being compared had exact angle combo. Same 80 lgf%, 40.8 pavilion, and I can''t remember the crown angle other than both were the same on both, tables were 56 % and 57 %. One diamond was .14 pts bigger in size than the other. The smaller one had fatter arrows and the larger had skinnier, very distinctly different. Is there another reason that causes the arrows to differ?

Differ in size or appearance?

Fatter vs. skinnier

 

[Missrocks]

Date: 3/1/2008 4:44:22 PM
Author: strmrdr

Date: 3/1/2008 12:58:23 PM
Author: Missrocks
Thanks Strmrdr and Garry for all the info!


One more question...The first time I saw the fatter vs. skinnier the two diamonds being compared had exact angle combo. Same 80 lgf%, 40.8 pavilion, and I can''t remember the crown angle other than both were the same on both, tables were 56 % and 57 %. One diamond was .14 pts bigger in size than the other. The smaller one had fatter arrows and the larger had skinnier, very distinctly different. Is there another reason that causes the arrows to differ?

let me guess the 80% was off a GIA report?
GIA rounds too the nearest 5 so 80 can be from 77.51 too 82.49 and there is a visible difference in the size of the arrows in that range.

Yes, it was a GIA report. I can see how rounding to the nearest 5 could have been the issue here.

Thanks!

 

[diagem]

Date: 3/1/2008 10:35:27 PM
Author: Missrocks

Date: 3/1/2008 2:06:50 PM
Author: DiaGem

Date: 3/1/2008 12:58:23 PM
Author: Missrocks
Thanks Strmrdr and Garry for all the info!


One more question...The first time I saw the fatter vs. skinnier the two diamonds being compared had exact angle combo. Same 80 lgf%, 40.8 pavilion, and I can''t remember the crown angle other than both were the same on both, tables were 56 % and 57 %. One diamond was .14 pts bigger in size than the other. The smaller one had fatter arrows and the larger had skinnier, very distinctly different. Is there another reason that causes the arrows to differ?

Differ in size or appearance?

Fatter vs. skinnier

No..., lgf''s are the reason..., assuming we are talking about a standard RB...

The angle of the main crown facets might change the viewing focus on a portion of the pavilion mains (which are the arrows)..., but not significantly enough to the point of making them appear fatter or skinnier...

 

[tankertoad]

I could grasp Brillianteering a little better...

 

[arjunajane]

no idea how to understand the aset images

ETA: but have decided to go do my homewk and stop being lazy, so js ignore me!