Part of the advertising campaign for diamond involves the "4 C's"
A lot is made of the fourth "C"- Cut- nowadays- and with good cause. The manner in which a diamond is polished really affects how it looks.
GIA grades the cut of Round Brilliant Diamonds- which certainly simplifies things for buyers.
But what about fancy shapes?
They are not graded for Cut quality by GIA.
Part of the reason is that there's so much variation within each of the shapes- unlike round, which is fairly standardized there's a huge variety of shapes that comprise "radiant cut".
Shape- that means LxW and the size of the corners- are only one aspect we need to look at.
We also need to look at how deep the diamond is, how large the table is ( that's the large flat facet on top)- and the crown and pavilion angles.
The top of the diamond is the "crown" the bottom is called "pavilion"- separating them is the "girdle"
The point at the bottom is called the "culet"
I've labeled these below
In this example, we are going to look at a stone which is a very shallow cut. Why would they cut it this way?
The reason has to do with the available piece of rough.
it might have been a very shallow piece- or this diamond was a piece sawed off the top of an octahedron.
The stone they came up with made excellent use of the rough- I'm sure they lost a far smaller percentage than the stone I used for comparison.
Say you start with a piece of rough diamond that weighs 1.65cts- that might polish out to a 1.00ct diamond.
In this case they might have started with 1.30cts rough
You'd expect there to be some penalty visually for this.
Fancy colored diamonds are really a different animal than colorless and near colorless stones.
I did not expect to like this stone- given it's large table
ITEM #: R4354
Radiant Cut Diamond, Loose
SHAPE: Radiant Cut
COLOR: W-X, Natural Light Yellow
MEASUREMENTS: 6.32 x 5.75 x 3.32 mm
TOTAL DEPTH: 57.7%
TABLE SIZE: 80(est)%
Here it is from the side
Below next to a stone with a taller crown
On many fancy shaped stone, crown height- expressed as a percentage- is sometimes considered.
Cuts like our Old Mine Brilliant stones have very tall crowns.
This stone has a crown I'd estimate at 7-8%
The stone in the diagram above has 13.5% crown height
It might be "logical" to assume such a stone would pay a heavy price visually.
This stone belies that.
Here it is face up next to the stone I used for comparison- a fancy intense yellow 1.03ct
There certainly is a price for the cut financially.
This is a one carat stone, that looks like a carat and a third- yet costs like a 3/4ct.
The fact that it's a diamond cut to emphasize it's yellow color- which it does successfully as well, I might add- give it different parameter as compared to a colorless stone.
Summation: We can point to the weakness of a diamond like this when judged against a benchmark that values crown height.
But we can also note that the cutter was able to produce a very lively stone- with a pleasant light return and fantastic size for it's weight.