Can you look at a diamond and guess the cut parameters?

[Flowery]

Given a head-on image of a round diamond, I feel like it can be easy to tell when it’s cut too deep or too shallow or if the table is too big. Are any of you good at “seeing” the effects of different crown and pavilion angles from a single image of a mounted round? Can you even see things like star length? I attached an extreme example of a GIA excellent cut and will post parameters if anyone thinks they can guess them based on the appearance. Happy new year!

 

[gm89uk]

The pavilion is the easiest to guess from the large table reflection, so maybe 41.6+, crown is harder to guess but typically shallower with this pavilion, so around 32. Table looks around 60, 80 LGF and the stars, I've never attempted to guess but I'm going for 45 on the report..

 

[Karl_K]

I've never attempted to guess but I'm going for 45 on the report..

Stars are not that hard, find the upper girdle facets, follow them into the point of the star then compare that distance to the remaining distance to the table. Roughly 50% in this case.

 

[Garry H (Cut Nut)]

The pavilion is the easiest to guess from the large table reflection, so maybe 41.6+, crown is harder to guess but typically shallower with this pavilion, so around 32. Table looks around 60, 80 LGF and the stars, I've never attempted to guess but I'm going for 45 on the report..

Pretty good GM.
I cheated using DiamCalc, but I was given my AKA by Martin Rapaport mid 1990's - When I first met him he gave me a few stones and asked me to play this game. I did pretty well and he has called me that ever since.

There seems to be a little bit of girdle painting going on also - top and bottom = lack of contrast.
You are closer than Karl on Stars - 46-47% my guess.
Lower girdles are a bit longer than you think - bigger table causes that trick.
Yes- its probably cut as a top of a much much larger stone and I bet it has a bruted girdle (but no money on that bet).

 

[flyingpig]

The pavilion is the easiest to guess from the large table reflection, so maybe 41.6+, crown is harder to guess but typically shallower with this pavilion, so around 32. Table looks around 60, 80 LGF and the stars, I've never attempted to guess but I'm going for 45 on the report..

This! .

Table is easy. Pavilion is relatively easy too based on the table reflection. Maybe 41.4+ or 41.6+. It is definitely not 41 or lower. LGH is easy as well.
Because the diamond shows good contrast with little leakage, it must have a shallow crown to complement the deep pavilion. So around 32.

 

[gm89uk]

This! .

Table is easy. Pavilion is relatively easy too based on the table reflection. Maybe 41.4+ or 41.6+. It is definitely not 41 or lower. LGH is easy as well.
Because the diamond shows good contrast with little leakage, it must have a shallow crown to complement the deep pavilion. So around 32.

Yes exactly, if it photographs nicely the crown should be roughly complementary.

These kind of threads have always been good fun

 

[Karl_K]

The pavilion might not be as deep as you think.
The arrow shafts are reacting to obstruction more so then the arrow heads where if its deeper the arrow shafts would be bright.

 

[gm89uk]

True, it really depends if we're trying to guess the true values or just the GIA rounded values

 

[Flowery]

Wow, you all are incredible! I especially appreciate that you gave the reasoning behind your guesses!

I only have the values off the GIA report, and I had no clue you all might be able to do better than the rounded values such that rounding would make a big difference. This might have made an interesting competition if the known numbers were more precise.

Here are the GIA values:
Table: 61%
CA: 32.5°
PA: 41.4°
LGF: 75%
Star: 50%
Total depth: 60.4%

Other info: Girdle is not bruted. There looks to be slight painting, but not enough to show up negatively on the GIA report. Carat weight is 1.01, so I’m sure the cutter was careful in keeping it over the 1 carat mark.

Thanks for “playing”—I learned a lot!

 

[flyingpig]

I like playing this game. I guess I was wrong with the LGF. The short arrows due to the large table reflection can fool you and may appear skinny. But it is just the thick base missing.