Sorry, Stupid question what is LGF% ?

[Carlosthejakal]

What is is and how does it work ?

 

[pricescope]

LGF - Low Girdle Facets.

 

[door knob solitaire]

I am glad that one was asked...and better answered.

It is my (given name) initials..and it drives me nutts when I see it here on the board. Thought you guys had some code about me!!!!

Low girdle facets...doesn''t sound like a complement. I guess it is necessary though. Just thrilled it is not about me!!

DKS

 

[JohnQuixote]

Date: 4/23/2007 11:59:17 AM
Author: Pricescope
LGF - Low Girdle Facets.

Commonly referred to here as Lower Girdles and LGFs (sorry DKS

).

They are called "Lower Halves" by GIA.

Remember that good crown/pavilion angles and top light return should be prerequisites. Once you have a diamond with great light return the lower halves ‘fine-tune’ the character of that diamond’s performance:

Shorter lower halves mean wider pavilion mains (what you see in diamond photos with obstruction as ‘arrows’). Longer lower halves mean narrower pavilion mains.As it relates to scintillation, broad flashes become more visible as lower half % gets shorter.Needlelike flashes become more visible as they get longer.Shorter lower halves can be conducive to performance in indirect/soft lighting conditions and longer lower halves conducive to direct/bright lighting conditions. Diamonds in the middle range have a balance of qualities.

The major labs generally include rounds with 70-85% lower halves as candidates for the top grade.GIA rounds to the nearest 5% on their reports. AGS does not round.

You can 'guesstimate' lower half % by viewing still diamond photos with obstruction (where the arrows are dark), like we commonly see on PS.The simulations below are near-Tolkowsky configurations. See how the 'arrows' get fatter with short lower halves - and skinner with longer.

 

[JohnQuixote]

The above are near-Tolkowsky diamonds like we commonly see discussed here.It’s a big world, with many different makes, and different configurations are impacted differently:For example, (X) lower half % would lend a much different appearance to a RB with a 50% table than one with a 65% table. Seeking well-performing crown/pavilion angles and top light return should be prerequisites. Once that is done, personal taste comes into play.

By the way; here is a page from GIA with graphics correlating to terminology on their reports.

http://www.diamondcut.gia.edu/05_diamond_anatomy.html