What does "star length" and "lower half" mean?

[Anniversary Girl]

On the GIA website, there''s a Report Check function that not only lists the usual measurements of a stone, but also the percentages for "star length" and "lower half." Does anyone know what this means, and if so, what is good? I''ve seen a lot of stones with a star length of 50% and a lower half of 80% on diamonds deemed by them to have "excellent" cuts.

Thanks in advance for your help!

 

[belle]

http://knowledge.whiteflash.com/Q10310.aspx

 

[WinkHPD]

Great illustration Belle!

The star facets are where the arrow heads come from and the lower girdle halves are where the arrow shafts come from when viewing a Hearts and arrows image in a viewer. Due to GIA''s rounding it is hard to know if an 80% lower half is actually a 78% or an 82% actual grade. An 82% is starting to get to be a real skinny arrow shaft.

I am too tired from my trip to remember all the exact percentages for great, good and yuck, but 50% for the stars is great and 78% for the lower halves is great. I would have to go refresh my memory to tell you where the edges are exactly from great to good and below...

Wink

 

[jasper]

This DiamondTalk thread explains how the Star : Upper Girdle ratio is measured:

http://www.diamondtalk.com/forums/showthread.php?t=15923

-- Jasper
----------------
http://www.folds.net/diamond

 

[strmrdr]

more info:
http://www.goodoldgold.com/Articles/MinorFacets/

 

[Anniversary Girl]

Belle, Wink, Jasper and Strmrdr,

Thanks for your replies and help with my question. Very much appreciated!

 

[MarkP1]

Is there any more info. on this topic?
I read through Good Old Gold and am a bit confused.
I too have seen a number of diamonds 50% star, 80% lower half.
Is there an ideal proportion?

Thanks.

 

[Ellen]

Date: 8/21/2006 8:19:18 PM
Author: MarkP1
Is there any more info. on this topic?
I read through Good Old Gold and am a bit confused.
I too have seen a number of diamonds 50% star, 80% lower half.
Is there an ideal proportion?

Thanks.

Doing a quick search, there''s this:

https://www.pricescope.com/community/threads/lgf-and-stars.36793/=

And this:
https://www.pricescope.com/community/threads/how-do-lgfs-affect-a-stones-appearance.48632/=

And this:

https://www.pricescope.com/community/threads/why-do-some-diamonds-look-dark-inside.35389/=

I''ll let you read and see if you come up with your own answer.

 

[MarkP1]

Ellen,
Thanks. I will take a read through.

 

[Ellen]

Date: 8/21/2006 8:34:22 PM
Author: MarkP1
Ellen,
Thanks. I will take a read through.

You''re welcome! Frankly, I found it all rather interesting, as these play a part in the stones personality.