Bold flashes vs lower and upper girdle facets

[Stephan]

I often read: "love those 76% LG, this diamond will have big flashes of fire".
I also love 75-76% LG, but I'm also happy with 80%.
85% however is not my cup of tea.
For example, what do you think of following diamond? (not talking about the price here)
Doesn't it have bold flashes in the Gemex report?
http://livereport.gemex.com/pid/2296858740
https://www.bluenile.com/diamond-details/LD10950326
Would you consider such proportions for buying or not and why?

 

[blueMA]

I often read: "love those 76% LG, this diamond will have big flashes of fire".
I also love 75-76% LG, but I'm also happy with 80%.
85% however is not my cup of tea.
For example, what do you think of following diamond? (not talking about the price here)
Doesn't it have bold flashes in the Gemex report?
http://livereport.gemex.com/pid/2296858740
https://www.bluenile.com/diamond-details/LD10950326
Would you consider such proportions for buying or not and why?

@Stephan checkout this GOG video. It'll answer your questions.

 

[Stephan]

@blueMA, I know this video.
My question was more: Would you consider such proportions for buying or not and why?
I would even consider a Solasfera. I love when the fire of the pavilion mains and the LG combines.

 

[Lula]

Yes. My 1.01 CBI was cut to these proportions. I the combination of longer LGFs with a slightly larger table (56 - 57) because, to my eyes, this combination looks brighter in office lighting and it really "pops" in any kind of spotlighting.

 

[Karl_K]

I think the difference is being over blown.
The shorter the lgf% less the lower girdle facets extend under the table and you get pin-fire instead of larger flashes off the lowers.
Fire off the lowers because they are pointed off from your face is more likely to happen.
Some people find shorter lgf% in a mrb over dark up close because a larger percentage of the diamond shows obstruction. Its not a huge difference but it can tilt a preference one way or the other.
Some angle combinations are complimented by different lgf%.
There are no free lunches everything is a trade off.

 

[bmfang]

On a GIA report, if the 80% is actually a 78/79%, that would be the upper limit for me. Of course, YMMV depending on your preferences.

 

[blueMA]

I would even consider a Solasfera

I saw a few of those in person and they weren't my cup of tea.
However, I do love 80% because they have less of obstruction issues and look brighter.

 

[Karl_K]

Here are virtual images at 75 to 80 lgf%

 

[flyingpig]

I agree with @Karl_K that the difference between the longer and shorter LGH is somewhat overblown. In addition, you also need to consider other angles (notably PA) and table %. For an example, I also like fat arrows from, say, 76% LGH, but not when combined with 54~55 TB and 40.6 PA; too much contrast.
But at the end, it is like choosing among jammy Californian Pinot Noir, med-full bodied Oregon Pinot Noir, lighter cool climate BC Pinot Noir. I like them all.

 

[flyingpig]

Here are virtual images at 75 to 80 lgf%

What are the TB, CA, and PA for these virtual diamonds, if I may ask?

 

[Karl_K]

75 next to 80

 

[Karl_K]

What are the TB, CA, and PA for these virtual diamonds, if I may ask?

These are 57t/34.5c/40.75p which is a good question because different angle combinations change the results somewhat.

 

[EncikG]

In a simplistic view, would it be right to say;
- 75%: more contrast, bigger bolder flashes
- And as you reach 80% or more: less contrast arrows, n giving up some bolder flashes for more pin fire?

 

[Karl_K]

In a simplistic view, would it be right to say;
- 75%: more contrast, bigger bolder flashes
- And as you reach 80% or more: less contrast arrows, n giving up some bolder flashes for more pin fire?

Larger flashes off the mains with a short lgf% but smaller flashes off the lowers.
Smaller flashes off the mains the longer the lgf% but you gain larger flashes off the lowers.

 

[jp201845]

These are 57t/34.5c/40.75p which is a good question because different angle combinations change the results somewhat.

Would it be fair to say with a combination of 56 T 34.5/40.8 would work well with both 75 % and 80 % LGF'S ?

 

[Karl_K]

The green arrow points to 1 of the mains and the red arrows to 2 of the lowers in this wire outline.
You can see how changing the size of one changes the other
.

 

[Karl_K]

Would it be fair to say with a combination of 56 T 34.5/40.8 would work well with both 75 % and 80 % LGF'S ?

yes

 

[jp201845]

yes

Thanks for your input Karl_K

 

[Karl_K]

In general 77-78 is near universal, working with the widest range of combinations and providing what is considered a well balanced appearance when obstructed.
That does not mean it is a universal preference however.

 

[Karl_K]

Almost forgot to link this:
https://www.pricescope.com/articles/do_pavilion_mains_drive_light_return_modern_round_brilliant
It might help to understand.

 

[Dancing Fire]

I think the difference is being over blown.
The shorter the lgf% less the lower girdle facets extend under the table and you get pin-fire instead of larger flashes off the lowers.
Fire off the lowers because they are pointed off from your face is more likely to happen.
Some people find shorter lgf% in a mrb over dark up close because a larger percentage of the diamond shows obstruction. Its not a huge difference but it can tilt a preference one way or the other.
Some angle combinations are complimented by different lgf%.
There are no free lunches everything is a trade off.

My wife's stone is 56% t , 34.5' crown and 80% LGF.
Mine is 54.3% T, 34.5' crown and 76% LGF.
Which stone looks better to me? ...of course I'm biased.

 

[sledge]

On a GIA report, if the 80% is actually a 78/79%, that would be the upper limit for me. Of course, YMMV depending on your preferences.

Pretty sure most here particpating already realize this but for those lurking or a future reader it's important to know:

• AGS reports LGF to nearest 1 degree (75, 76, 77, etc)
• GIA reports to the nearest 5 degrees so a range of values is grouped together
  • GIA 75 = 73-77
  • GIA 80 = 78-82
  • GIA 85 = 83-87
• Tend to see a bulk of super ideals with 77-78 as they utilize AGS reports, although occasionally see other values as well

 

[gm89uk]

I've found with higher crown / lower pav combos a higher LGF is required. So for a 36/40.6 combo, an 80% LGF would be great.

 

[sledge]

Just a suggestion but it would add value to this thread to link a specific diamond with properties you talk about so there is visual sensory that goes with the words.

Also might be easier to use samples from the same vendor site so everyone would have the same type of images and videos to look at and compare.

 

[flyingpig]

I've found with higher crown / lower pav combos a higher LGF is required. So for a 36/40.6 combo, an 80% LGF would be great.

Here is an example of 53/36/40.6 (40.5) combo with 75% LGF.

High crown is good, small table is good, fat arrows are good. However, when you have everything, it is not necessarily the most desirable.
https://www.jamesallen.com/loose-di...rat-h-color-si1-clarity-ideal-cut-sku-4369664
Not an ugly stone. I would buy it at a right price. But, not my first choice.

 

[Karl_K]

Just a suggestion but it would add value to this thread to link a specific diamond with properties you talk about so there is visual sensory that goes with the words.

Also might be easier to use samples from the same vendor site so everyone would have the same type of images and videos to look at and compare.

Against the rules for me to do so, but feel free to do it if you want/have time.

 

[Karl_K]

I've found with higher crown / lower pav combos a higher LGF is required. So for a 36/40.6 combo, an 80% LGF would be great.

A shallow pavilion with longer lgf% minimizes the effect of obstruction issues.
With a slightly steep deep combo longer lgf% removes under table leakage.
GIA gross rounding complicates matters.

 

[Karl_K]

Table size also changes the ratio of mains vs lower halves under the table with the same lgf%.

 

[blueMA]

Ask yourself while looking at your sparkling diamond. The bigger the surface area of a facet, the bolder and more far reaching the light flash. Which facets do you notice the most? What constitutes the chunkiest of the facets on a diamond? Chunky facets also come at the expense of reduced overall scintillation.

 

[blueMA]

https://www.heartsandarrows.com/hearts-arrows-ideal-cut-diamond-creation.aspx