The cut of a Diamond is the only property which is totally dependent on man. Although often overlooked, cut is actually one of the most important aspects to consider when choosing your diamond. A Diamond cutter analyzes the rough diamond, and has to determine how to extract the most beauty and most profit out of the rough stone.
Cut refers to not only the shape of the diamond, but its proportions and finish, factors which determine the sparkle of the diamond.
It is possible to take the same stone, and depending on which method the cutter decides to use, to either cut it into the most beautiful stone it can be despite heavy weight loss and perhaps lower monetary value. Or else, he can cut a stone to its maximum weight and monetary value, but lose some "brilliance" and "sparkle".
You see, even if you have two equal polished diamonds, both the same carat size, both the same color, both the same clarity, they may look completely different. How? There are many different shapes and facets in a diamond. The weight can be distributed in different parts of the stone.
The goal in terms of extracting the greatest beauty from a Diamond, is to have light enter a Diamond, disperse the light as it bounces inside, thereby producing the different colors and sparkly effect, finally returning as much light to the eye as possible.
According to conventional wisdom, the proportions shown at the top of this page are the best for maximum light return. The 2-dimensional illustration below shows the theoretical path a ray of light will take through an ideal-cut Diamond. . As you can see, the rays of light entering the Diamond, reflect back to the eye. But it is possible for a diamond cutter to extract more weight out of the diamond by increasing the diameter of the stone. This will make the stone too shallow, and light may escape from the side of the stone, as shown here... or leak out of the bottom of the stone, like here... Another side-effect of cutting this way is that it makes the stone appear larger. However, the fact that it appears larger than it is does not make it a better stone. If you compare a shallow stone to a well-cut stone, you will see the difference in how the well-cut stone "lights up".
By the same token, it is common to see the opposite problem. A stone which is cut too deep will "leak out light" in much the same way as the shallow stone. Here are two illustrations . . .
1) and 2) .
This is not to say that a shallow or deep stone is a sign of a poor, or "low-quality" diamond cutter. Sometimes the shape of the rough diamond makes it impractical to cut a stone closer to "ideal" proportions without losing significant weight. But it is important to note the "light leakage" which will result from this cut.
One final note about cut. In the years since we've put up these tutorials, much has changed in how cut is perceived and marketed. A serious push was made to introduce systems of cut evaluation. There are many proponents of these new systems, however the technology behind it is not very impressive nor scientific. Computer simulations that do not take into consideration many of the variables that affect light return are being used as the basis of new cut grades by the gem labs. They do not compare to having an expert looking at a cut and judging it with the naked eye. And more importantly, cut is more subjective than the other "c"'s. While there is a clear reason to prefer the rarer 2 carat diamond to a 1 carat diamond, or a clear preference for a D color over a G color, some people prefer diamonds to be cut different ways. Some like bigger tables. Some find different proportions more pleasing. Some prefer fire over brilliance and vice versa.
According to GIA:
A polished diamondís beauty lies in its complex relationship with light: how light strikes the surface, how much enters the diamond, and how, and in what form light returns to your eye.
The result is a display of three attributes. Brightness is the combination of all white light reflecting from the surface and interior of a diamond. Fire is the colored flashes that can be seen in a diamond. Scintillation describes the sparkle of light you see in a diamond, and the overall pattern of bright and dark areas when you look at a diamond face-up.
A polished diamondís proportions affect its light performance, which in turn affects its beauty and overall appeal. Diamonds with good proportions optimize the interaction with light, and have good brilliance, fire, and scintillation.
The Design (weight ratio, durability) and Craftsmanship (polish, symmetry) of a diamond also affect its cut quality, and are considered in determining a diamondís GIA Cut Grade.
Can you see from these sentences alone what the problems are? For example, brightness is white light. Which by definition takes away from Fire which results from Dispersion. How much Brightness is preferable to Fire? It's all so nebulous. The number of variables are too great to measure all this.
In the exuberance to bring a definitive cut grade to the end consumer, something has been lost along the way. Our advice to you is to ignore the official cut grades and judge the cut by how your eye finds it pleasing or not.
Anecdotes from the Lab:
All major cutting styles of diamond has a plot to match it. The plot diagram reflects all the facets on that diamond with the exception of the girdle. Inclusions are marked on the plot. However, sometimes new shapes or modified shapes come in. It isn't usually a problem even if the pavilion plot of one diamond is different than the crown diagram it usually goes with. However, it can be tricky when no plot matches the diamond! In these rare cases, look at the comments to decipher how the graders decided to proceed with the plot.
Cuts for Collectors
Rose Cut Diamond
Portuguese Cut Diamond?
Cyclone cut diamond??? (Tycoon Cut)
Phoenix Cut Diamond
What is a full cut Diamond?
Duchess cut diamond
Pics of fire rose cut diamond
The Zoe cut Diamond... only 12 cut a year??
DIAMONDS TUTORIAL NAVIGATOR
Real Graders Don't Drink Kool-Aid
Lesson 1, The 5Cs:
Carat, Color, Clarity, Cut, Cost
Lesson 2, Shapes:
Round, Asscher, Cushion, Emerald, Heart,
Marquise, Oval, Pear, Princess, Radiant
Lesson 3, Articles:
How to Buy a Diamond, How to Sell Your Jewelry,
How to Read a Diamond Certificate,
The difference between a Certificate & an Appraisal,
What is the SI3?,
World's Largest Polished Diamonds,
World's Largest Rough Diamonds, Diamond Facts
Gem labs and the science, art and marketing of diamonds