Impact of Lower Girdle Percentage on ''''personality''''

[deggles]

I''ve got a question that is a follow-up from a different thread. Rhino provided the following series of 4 images for H&A stones that have everything held constant except the lower girdle percentages. Based on everything else being held constant, and lower girdle percentages ranging from 70-85%, how would the ''personality'' of the stones differ based only on the lower girdle percentage.

Thanks in advance,

Deggles

 

[valeria101]

Not sure what you mean... the 70% looks like a cross between OEC (Old European Cut) and modern brilliant to me. Those larger looking patches of light almost add up. These should be stones with more fire and contrast - much like the oldies as well.

The other extreme is a bright white stone with less contrast (the black on the arrows provide much of the contrast, as understood here).

I don't think I can describe these things very well. And have yet to see a photo comparing the types... it must be very hard if even possible to achieve.

Any chance you could pass by Good Old Gold ?

If not, Gem Adviser models might be the next best thing (there are a couple of relevant ones down here).

 

[deggles]

valeria,

Thanks for the link, that was a great little tutorial on the minor facets! I''ve already bought my stone and I''m trying to learn as much as possible about it. Luckily, I''ve been pleasantly surprised with the overall quality of my ACA stone as I''ve dug deeper. Sometimes, as you gain knowledge, you uncover some characteristics of your stone that would have pushed you toward a different stone, but that hasn''t been the case

.

Unfortunately, the Sarin report for my stone doesn''t include minor facet measurments. Based on my idealscope image below, would I be correct in the assumption that the lower girdles are somewhere between 79-82 percent? It seems that the shape of the arrows more closely match the 80 percent range than anything else.

Thanks again,

Deggles

 

[deggles]

I keep getting an error when I try to post the image...I''ll keep trying.

 

[deggles]

 

[strmrdr]

It gets complicated because the crown and pavillian angles and and the star facets can change the effect of the different lgf%.
Keeping the lgf% and the stars and girdle the same but change the crown/pavilian from 34/41, 34.3/40.9, 34.5/40.5 and 34.9/40.9 will all have different personalities.
No one set of facets stands alone.

Your aca is in the 77-78% range.

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.

 

[jelyjelo]

Hi strmrdr, (don''t mean to steal your thread deggle, just want to post my questions here so we can all lean together. Since I
just got my new RB too and curious about the minor facet numbers)
Luckily I''ve got Sarin 3D viewer result with angle info of all the facets, but no percentage info. So I am having hard time to interpret the result using the knowledge I''ve learned from GOG''s website. If I list all the angle info here, would you help me understand them please?!

table: 57.3 57.0 57.2 57.2 -- avg 57
depth: 61.2%
girdle: 1.2% - 1.6%
crown: 34.6 34.7 34.4 34.5 34.4 34.6 34.5 34.7 -- avg 34.5
upper girdle: 44.0 44.3 42.7 42.6 42.2 42.5 42.4 41.8 42.6 42.6 42.4 42.6 42.0 42.4 42.7 42.3
star: 24.3 25.0 22.8 22.9 22.5 23.1 22.9 23.2
pavillion: 40.8 40.8 40.9 41.0 41.0 40.9 40.8 40.8 -- avg 40.85
lower girgle: 41.8 41.9 42.0 41.9 42.0 42.0 42.1 42.1 42.1 42.0 42.1 42.1 42.0 42.0 42.0 42.0

There are some % numbers on the graph but I don''t know what they are referring to.

Star/Upper Ratio: 58:42 -- what''s this mean?

Thanks!

 

[strmrdr]

jelyjelo,
There is enough info there that someone with diamcalc should be able to get the rest of the info I think.
I can tell a few things by the info given but prefer to wait for someone more knowledgeable than I am.

 

[JohnQuixote]

Date: 4/7/2005 12:34

0 PM
Author: deggles
I keep getting an error when I try to post the image...I'll keep trying.

Deggles, here's an assist

LGF @ 78%

Strm's assessment, above, is quite good. For more discussion on these "character" differences created by minor facet differences, see this thread. (particularly bottom of page 1 and top of page 2).

Also, some mentions at bottom of 1, top of 2 in this discussion of new GIA grading.

And, again bottom of 1, top of 2 in this AGS grading discussion.

 

[Rhino]

Was able to hop on for a moment.

John... clarify ... does that stone have 78% lower girdle "length" or lower girdle "depth"? From the looks of the image it appears to be depth and not length.