- Joined
- Feb 26, 2003
- Messages
- 379
echelon6 says:
I read the article you linked to a while back last night and I didn''t find much explanation on why the LGF sweet spot is at 77.5% except that you mentioned that several groups and experts all agree?
I was thinking exactly on the same line as the Everest - Himalayan example. The ideal LGF answer being the arithmetic midpoint only applies if performance varies linearly with LGF. But as with many things, linear relationships are somewhat rare in real life, so at the moment without further explanation, the LGF midpoint theory doesn''t seem logical to me.
Could you please elaborate?
echelon6,
Strm’s answer to Pyramid is right on. when he says:
“I get into arguments with some of the experts on that all the time. I think a lot of consumers can see the differences, I can, but some can’t.
The question becomes when do the differences matter.
That is the heart of the issue. There is no question that different lgf% give a different look The argument is at what point does it become a performance issue rather than a personality difference. Strmrdr
From my previous post you know that I am not saying that the sweet spot center of 77% in pavilion half length is any better in GIA’s opinion or mine than any other % within our respective sweet spot ranges. What I personally like best is the larger flashes of sparkle and fire reminiscent of Old European cuts that come from larger mains closer to 76%.
As the pavilion half length exceeds 80% the mains get too thin to provide large flash sparkle and fire, but their scintillation is great in jewelry store lighting, which is likely why they are cut that way. So my opinion and that of the cutters of optically symmetric Ideals that I spoke to seem to converge in the vicinity of 77%.
I thought it was another fairly remarkable accordance when I learned that GIA had hard limits of 70% to 85% on LGF%, which gave the same sweet spot center.
In a conversation with Al Gilbertson, I learned that their statistical analysis of the paired comparison testing revealed an answer to Strm’s question of when does lgf% become a beauty/performance negative rather than just a personality/ pattern difference. Under 70% GIA found that the halves were too small and those stones were seen as deficient in sparkle/scintillation. Exceeding 85% caused the pattern to be seen as too “splintery”.
My detailed explanation for why I choose 77% as the sweet spot center of Ideal LGF% is too long for here, but it contains supporting diamond photography and DiamCalc images. I would enjoy hearing what everyone thought of it.
My conclusion was that the best balance between the areas of the main reflections with their large flash sparkle and fire, and the area of the halves, which provides more sparkle/scintillation is obtained with a 75% to 80% length of the pavilion halves.
In deference to Wink I do find larger main, well cut Old Europeans with their glorious, large flashes of fire and sparkle are in a beauty class of their own. Diamond cuts with too long halves with too thin mains lack this key component of the Essence of the Ideal.
Ideal regards,
Michael