Grading A Diamond's Cut
 Cut height is (in my opinion) the most important factor in a diamond's brilliance. Since it's all about light optics and the ideal angles to produce the maximum effect the cut is critical to the beauty of the diamond. An excessively deeply cut stone will also affect the way the light passes and reflected in the mass of the diamond. A very shallow cut stone will seem dark, as the light exits the back of the stone, the angles not reflecting the light back up through the top of the stone to your eye. If it sounds like this is critical, it is... In a round stone you should try for 58-60 degrees in total depth, with the table at about the same for a bright diamond with fire and life.

The Round Brilliant Cut is designed to provide maximum optics for the brilliance and scintillation,
making the light seem to sparkle and dance in the light.

Fancy cut stones (Marquise, Emerald, Pear, Princess Cuts) are all ways of cutting a stone to maximize the carat weight. A rough diamond which might only yield a half carat in a Brilliant Cut might yield another 50% if cut into a pear shape or marquise. In fancy shapes it makes sense to add a few percent to correct for the shape of the stone, and transition from the optimum shape, which is the round. A fancy shape that's shallow is not worth having, and if the stone is over 70 percent do not even consider it... A marquise should have an aspect ratio of 2:1 for the classic shape, but shorter is always better than long... Watch out for extremely thin girdles too... All the comments on the Certificate , and all those comments are important to both the value and the beauty... Many of the fancy shapes are stunning.
How about we take a look at just a few of them now?




The Round Brilliant

The most common, and most "brilliant", diamond cut is the Brilliant Cut, a.k.a. the Round Cut, American Ideal Cut, or American Standard Cut.

Back at the turn of the century, Marcel Tolkowsky, a member of a large and powerful diamond family, calculated the cuts necessary to create the ideal diamond shape. As part of his PhD thesis in mathematics, Tolkowsky considered variables such as index of refraction and covalent bond angles to describe what has become known as the brilliant cut.

Marquise

Looks something like a football, when viewed straight down from the top. Some Marquise are cut too thin and suffer from a markedly dark center (commonly called the bow tie effect). This effect is eliminated by paying attention to the depth (want lower sixties) and the crown height (want close to 14%) The light passes through the back of the stone due to the criticality of the angles needed to reflect the stone being too steep. Stay in the sixtie percent range for this lovely cut, and avoid extremely thin girdles like the plauge!!! If you're offered a stone under 58% it will only look good under halogens :)

The ideal ratio of length to width should be about twice the length as the stone is wide. (2:1 aspect ratio) In this shape is is so important that the cut not be too shallow, if the stone is flat and wide the same optical effects problems present themselves as a markedly less bright and beautiful stone... You also want to remember that with a fancy shape stone you want to keep the color up there, as only the round stone provides maximum brilliance the fancy cuts show color faster than a well cut round stone will...

Oval

Has an elliptical shape when viewed from the top.

For both the Oval, the ratio of the length to the width should be about 1.5:1 If it is much greater then that you will see a dark area. This is commonly called a bow tie effect, "undesirable". If the ratio is much less then 1.5:1, the stone looks like a misshapen round. A well cut oval stone can be nearly as bright as a well cut round brilliant shape, the angles are closer to ideal for the maximum optical effect that well cut diamonds can produce... Trust your eye to judge the cut, if an oval shape looks lifeless in natural light odds are it's a very poorly cut stone.... (No fair cheating with dozens of recessed halogen lights in the retail store :) Stay with lower sixties in depth for this cut.

Emerald Cut

Looks like a rectangle from the top, with truncated corners. These can be beautiful stones, with stepped facets the sheen tends to be large flashs of these stepped angles on the pavilion of the stone... With this cut I feel that color plays a very important role in the beauty off the stone, color tends to show very dramatically in emerald cut stones so stay up above "G" for a super look.

Note that this pictured stone is longer than most you'll see, again it's common for aspect ratios to vary greatly in fancy shape stones, which tend to be cut to maximize the diamond crystal, so you could say that the stone "tells" the cutter what shape it wants to be to yield the largest and most precious finished stone... Stay about also in the sixty percentile range depth here, with a 1.5:1 aspect ratio for a great look.

Pear Shape Cut

A popular cut that looks like a tear drop. This is a traditional cut which is perfect for pendants, drop earrings and many applications. Here it's a good thing to concentrate on the girdle at the point and make sure it's not so thin that it's unstable. You want to find a nice pear shape that is well cut, with a polished girdle ideally... Remember that really excess weight will cost you appearant size, so watch that depth percentage.

You want to make sure the stone has good depth as well, a shallow stone is not only more dangerous than a well cut stone, it's also not nearly as bright. Once again it's the critical angles and reflection of a well cut stone that's the key to its beauty... Stay 61-64% here in depth, and head for that 1.5:1 aspect ratio for a great look and lively diamond. Color also shows fairly dramatically in a pearshape cut; all fancy cuts tend to show lower colors more significantly than a well cut round stone...

Trillion Cut

(Or variations of this spelling) are three sided cuts.... Many of these cuts are trademarked cuts. The triangle cut tends to be a stepped facet cut while the "Trillion and other variations of this more modern cut are based upon a brilliant style cut... The fire and beauty of these cuts is spectacular, they are wonderful cuts...

Trillions are basically triangular in shape, usually with truncated corners, with a variety of facets. Quadrilliants, Squarilliants, Princess Cut and such, are square when viewed from the top. Note that this pictured stone has bowed sides, so it's not based on the straight triangle cut but tends more to follow the brilliant round's facet style... Depth here is OK through the mid to high sixties ( 61-68% ) but avoid deeper or shallower... Don't be put off by seemingly huge tables, a 70% in no problem in this cut.
Princess Cuts & Specialty Cuts

There are many variations of the cuts listed above, some subtile variations and some are extreme. Called by other names, (Squarillion, Quadrillion and others) the square cut fancies are both bright and beautiful due to the brillianteered cut! Smaller rectangular cut diamonds, which look like small boxes, or like tapered boxes, are commonly called baguettes. Baguettes tend to have stepped facets, more like the emerald cut has, pictured is a princess cut stone, a melding of the brilliant cut with a square style cut yields a beautiful modern cut... Bagguettes are not as bright as the brillianteered stones.

With the many various shapes, and a good working knowledge of how diamonds are graded you can use your eye to measure the over all effects of these cuts and pick the one that's just right for you...

Additional Data about Cut...
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