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The Diamond Grading Four C's
A practical guide you can actually use!

In diamonds there is a rich and diverse choice of shapes, each has a different way of working with the light. The range of cuts available are wonderful, but it is true also there is not another cut that comes close to the round brilliant well cut idealcut in light return or sheer dazzeling activity, the princesscut comes the closest I think in the fancies but the round diamond stands as the definition of maximum beauty and brilliance that a diamond is capable of producing. I will review some of the more popular cuts as I go on, and will also explain a bit about what the cut paramaters should be and some important things to consider about each of the cuts and shapes. When I refer to the term that a diamond should be "Well cut" I mean that it's geometry and finish, symmetry and make should be perfectly fine, many still do not realize that for diamonds the "CUT" best refers to the shape, at least in relationship to the "Four C's" that is...

The "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. This is by far my favorite cut, having the brilliance and fire that no other cut really approaches. A large table (over 64%) can really kill the diamond's beauty, and a stone which it too shallow will also "die optically"... Where a great place to be is in the 58.5-62% depth, and a table size in the mid fifties, but to about 60% safely for beauty. This is practical, and can be verified, and is the truth...

The AGS defines "Ideal Cut" as a range of Table diameters between 53-57%, Crown Angles at 34-35%, Crown Height at 15-16.5%, Girdle Thickness at Thin to Medium, Pavilion Angle of 41% with the Pavilion depth at 43-43.5%... Culet at Very Small/None with total depth at 60-62% for their cut grade of ideal... We're talking perfect alignment of the crown and pavilion facets, strict symmetry and a mirror like polish... "No polishing lines or wheel burns need apply"... Modern Jewelers magazine has a great article this month on Ideal cuts... Various cutters have slightly varied definitions of the ideal cut, but if you keep the table size in the mid-fifties and depth between 54-60% you will have a fantastic diamond, and look. I've often said that if the consumer remembers that they have a solid basic understanding to avoid off cuts and poorly cut stone... With certificates and lab reports you are able to completely qualify a diamond you are considering, minus all the sales hype and junk...

I wished that GIA gave the more complete dataset for diamond in their lab reports, like crown height and pavilion depth, but I'm sure that they will find it necessary to revise their format soon now that AGS is offering a more complete report. Not everyone's perfect diamond is an AGS (000) Hearts and Arrows diamond, there are wonderfully fine diamonds in the up-to 60% table ranges that are much more affordable which might be perfect for your world. Diamonds are not discounted for poor cuts to about the 64% table size, which is terrible on the optics of the diamond. Even the Rapsheet is based on the "A" catagory with tables to 63%. "Screwy Cuts" are discounted heavily they are also much less beautiful as well, so make sure you are comparing apples to apples... Stones with deeper cuts, or larger tables will be discounted, but you can be sure that if you confirm to a narrow range of specs we've discussed here that you will do very well. I really like some stones which have table sizes up to 60%, and often times the visual difference between an AGS (000) ideal cut, and fine premium cut with a slightly fuller depth or table size just out of range is practically nill, when the price difference is vast... Beauty to me is taking the five C's into harmony, cut, color, carat, clarity and "cost"... While I really like the table sizes in the mid to higher fifties I'm a sucker for a 57.8%-60% table on a stone that is both well priced and beautiful... Great diamonds and beauty exist acoss a ample and wide range, and that is also where maximum value lives too.

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 :) If you can stay in the lower 60's in depth in your marquise this will relate to a larger size, deeper stone are often the same weight but will be of a much "smaller appearant size"... Really hit that 2.1:1 aspect ratio on the nosey too folks, for the shape of the stone is everything in the marquise... For a bright stone watch that depth carefully!

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. Another consideration is clarity in the emerald cut, since it's a step faceted stone you won't hide imperfections easily in this cut, you should stay in the VS1-2 range as a minimum here folks, for a bright and clean stone.

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. Also watch that depth here too folks! 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... Do not buy a stone less than 58% for the optics will be seriously a problem in this shallow depth.

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 & Other 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. I love the princesscuts for the fire and the life of the diamonds, they are best kept in the mid sixties to lower seventies in depth and generally folks want square shapes more than extreme rectangles. 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...