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1.75F VS2 vs 1.80F VS2 (GIA Reports provided)

graciegracie

Rough_Rock
Joined
Aug 4, 2011
Messages
2
Hi Everyone,

I'm trying to decide which of these two stones is better. I have the GIA reports for both but haven't seen the stones in real life. There is a $200 fee in calling the stone in so I was wondering what people thought about each. There is little price difference between the two (not a deciding factor).

Thanks
Gracie
 

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sarahharris

Rough_Rock
Trade
Joined
Jun 23, 2011
Messages
21
If the price isn't much different, and quality is about the same, I say go with the 1.80 diamond. The reports are a little hard to read, but if all things being just about equal, I would go with the slightly bigger diamond.
 

kelpie

Ideal_Rock
Joined
Jan 8, 2008
Messages
2,362
Can the experts chime in on the 36+ degree crown angles? Seems out of norm.
 

farmer gal

Brilliant_Rock
Joined
Mar 26, 2011
Messages
1,063
I don't know where you are looking at buying, but JA will look at three stones for you free of charge and tell you which one preforms the best.

I don't know what your budget is, so I'll let you look around. But for example this is a G, but it looks like a great stone, and the average person will most likely not be able to tell the difference between an F and a G.

http://www.jamesallen.com/diamonds/G-VS2-Ideal-Cut-Round-Diamond-1323621.asp
 

centralsquare

Ideal_Rock
Joined
Jan 18, 2009
Messages
2,201
There are better experts here but my first thought is that the specs of the second don't look quite as good as those on the first (but I'm not sure I can read the numbers perfectly). Which vendor are you working with? Many of the PS vendors have images online that will aid in selecting a stone for you.
 

Stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
Messages
14,069
Number are much more promising for the 1.75c stone. Can the vendor get idealscope image for these stones?
 

John P

Ideal_Rock
Trade
Joined
May 1, 2008
Messages
3,563
Here are some thoughts which I hope are helpful.

First: No one will be able to tell you decisively which one to select from afar. There are too many potential variables which are undisclosed on a grading report. As an example, the single number given for Pavilion Angle is an average of 8 different facet measurements. So the 41.0 PA (1.80) could imply close measurements of 40.9, 40.9, 40.9, 41.0, 41.0, 41.1, 41.1, 41.1. Or those facets could stray much farther from the average, like 40.2, 40.5, 40.6, 40.8, 41.0, 41.3, 41.5, 42.0, resulting in potential performance reductions. Furthermore, even the averaged PA number gets rounded to the nearest 0.2, so the actual average could be closer to 40.9 or 41.1 - but rounded to 41.0. We can't tell from the grading report.

It's the same with Crown Angle. That number is also an average of eight separate measurements, rounded to an even more extreme degree (the nearest 0.5). Star length and lower-half length are treated similarly, rounded to nearest 5% - and the lower half number includes 16 different measurements.

As an aside, the nicely in-round mm given for both diamonds indicate (arguably) to me that they're less-likely to have wide swings in primary angles. But without further information or images there is no way to know decisively.


Second: While not-decisive, I can give some opinions regarding these numbers.

In terms of cut-quality the 1.75 appears to be in a better class (bearing in mind this is a prediction based on these averaged & rounded measurements). Its primary angles have a solid relationship, with a high crown that may result in abundant dispersion in many lighting conditions - again depending on cut specifics. In actuality the crown may be a tiny bit higher than indicated on the report (due to rounding) since the model I created is 2 points lighter. This is a non-issue with this pavilion/crown combination. I think this diamond has great potential based on the data given.

The 1.80 bothers me in a few respects. For one thing, the pavilion/crown pairing will definitely result in some light leakage, regardless of cut-precision and other specifics. The AGSL cut-charts project a light performance grade of 3-4 for this combination (again, that would depend on specifics). The diamond is also right at the 63% depth threshold, which is the EX/VG cutoff for GIA when it comes to RB spread. That means if the crown or pavilion rounding is concealing any depth whatsoever the diamond may actually be VG in cut. Based on the data given I calculated it to be 63.1%.

The short story? Looking at the mm spread of these candidates it would take a superhuman to see any size difference when they are mounted: 7.69mm avg versus 7.73mm avg. Additionally, the 1.75 has safer indicators overall than the 1.80. If I was looking to purchase a diamond for a store and they limited me to bringing in just one I'd call in the 1.75.

Again, without more information it's impossible to be decisive, but I hope the info above is interesting.

*

Here are DC-generated images. These wire frames are based on the averaged measurements and only show "best-case" overall light-return vs leakage. They are not diamond-specific.

1.75


1.80

175-f-vs2.jpg

180-f-vs2.jpg
 

Regular Guy

Ideal_Rock
Joined
Jul 6, 2004
Messages
5,954
sarahharris|1312469247|2984007 said:
If the price isn't much different, and quality is about the same, I say go with the 1.80 diamond. The reports are a little hard to read, but if all things being just about equal, I would go with the slightly bigger diamond.

Sarah, say it ain't so!

I valued John's input, too. But, was btw thankful what I regarded as his analysis ( and Stone Cold, I might add) matches with the conveniently linear presentation of the HCA: 2.3 (nearly fine), and 5.6...not so good.

Also, the 2.3 is FIC-ish, consistent with John's comments, too. Mama like. But, better to see, so I'll add the qualifier too.

Regards,

Ira Z.
 
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