Help me with this diamond

[newuser1982]

Hi! could you take a look at the below diamond and let me know if it looks okay?

 

[flyingpig]

The images are flawless. What are the proportions? Or GIA report number if the stone is on hold.

 

[newuser1982]

http://images.b2cjewels.com/Images//Certificate//8528166.pdf

Here is the GIA cert - angles are not perfect (33 / 40., but otherwise looks fine to me

 

[flyingpig]

Great spread, great light return, fat arrows for bold flashes.

Potential deduction in dispersion.

As long as you fully understand what you are getting, it may be an excellent choice.

 

[ChristineRose]

The pavilion is actually 40.8, which is a world away from 40.

The crown is slightly shallow at 33 degrees. You can see this in the Idealscope where the image is almost all red, except for the unusually small white triangles. These diamonds trade some contrast and scintillation for extra brightness.

The HCA tends to favor diamonds that push the shallow/bright/flat side of the envelope and not everyone agrees with the HCA on this point. But it's still a superb stone especially if that's your taste.

 

[newuser1982]

thanks - what do you mean by "Potential deduction in dispersion". Is there a GOG youtube video or something that you could point me to explaining that?

 

[flyingpig]

thanks - what do you mean by "Potential deduction in dispersion". Is there a GOG youtube video or something that you could point me to explaining that?

At least, according to AGS's grading system, light performance can be further divided into four sub-categories:
brightness, leakage, contrast, and dispersion (fire)

As you can see from the ASET/IS, the diamond has no issue in brightness (great amount of red), leakage (very little or almost no white), and contrast (clear well defined blue/black arrows). Unfortunately, the ASET/IS does not tell anything about dispersion/fire (or how light is bent to produce different colors); think about dispersion PRISM. This is directly impacted by the crown/pavilion angle combo as well as the table size.

I often see 33/40.8 combo does not score high in dispersion/fire. I say "potential" deduction, because you do not know for sure unless you have the diamond 3-D ray traced and analysed by a software.

This is why people often recommend crown angles between 34 and 35, despite the fact that a diamond with 33~33.5 crown angle can look flawless in the IS/ASET scope and in magnified images. Some have desire for small table/high crown angle combo for fire, while others focus on spread, light return and no leakage.

Is this a beautiful diamond? I think so. Is it for you? Only you can tell.

I do not believe there is a video comparing diamonds with different crown angles, say.. 33.0/40.8, 33.5/40.8, 34/40.8, 34.5/40.8, 35/40.8, and 35.5/40.8.

The below document contains "dispersion deduction" chart (pg 119)
https://www.americangemsociety.org/Content/uploads/85441435072031.pdf