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        Round Shape Diamond
 
By far the most preferred diamond shape, the round-brilliant cut is also the most optically brilliant because of its 360-degree symmetrical shape. A round brilliant is a great choice if you want the most sparkle and the most enduring classic shape. The round shape has been cut for centuries, but in 1919, Marcel Tolkowsky defined specific angles and proportions to yield the most brilliant diamond, which form the basis for the modern "Ideal" cut round-brilliant diamond. Round-brilliant diamonds are the only shape to have this ideal proportion defined. The round silhouette works with almost every mounting, from classic solitaires to the most avant-garde designs. Rounds can be set into four or six prongs, based on the design of the setting, or into bezel mountings (a metal band that runs around the edge of the diamond to hold it securely in the setting). In general, if the round brilliant has an Ideal cut or Very Good cut, you want the setting to have the least amount of metal around the stone so that it is held securely but does not cover up too much of the diamond and block light from entering the stone.


     Princess Shape Diamond
 
The princess cut is a modern classic of clean, square lines and beautiful sparkle. This shape is the perfect choice if you prefer a square or rectangular outline but want the brilliance of a round. Developed in the 1970s, the princess cut is now second only to the round brilliant in popularity. The cutting of this diamond combines the step-cutting of the emerald cut with the triangular facets of the brilliant cut and is cut with right-angle corners. Although most prefer a square outline, some stones are cut with a slightly more rectangular outline. The princess cut works beautifully as a solitaire but also looks great paired with side stones, especially trillions or smaller princess-cut diamonds. It is important to protect the more vulnerable corners with a V-shaped prong at each point.


 
      Emerald Shape Diamond

The emerald-cut diamond is among the most classic of diamond shapes. Its clean lines come from step-cutting, or parallel line facets. It is always cut with blocked corners and is usually cut to a rectangular outline, although a few are cut to be more square. Because of its simpler faceting structure, larger inclusions are sometimes more visible to the unaided eye, so diamonds cut in this shape usually need to be higher clarity (I1 or I2 clarities should probably be avoided). Length-to-width ratios should be considered when choosing an emerald cut: Usually a 1.50:1.00 ratio is preferred, meaning that the length of the stone should be about 1½ times the width of the diamond. However, like all fancy shapes, personal preference prevails, and some may prefer a squarer outline, or longer, thinner rectangle. An emerald cut is loved by purists and looks especially wonderful set in platinum, in a simple setting or a baguette side-stone setting.



      Asscher Shape Diamond

This elegant shape is a variation on a classic emerald cut, developed in 1902 by the venerable Asscher brothers in Holland. The Asscher cut is not a traditional choice but has gained deserved exposure recently because of celebrities wearing the cut. The uniqueness of this shape is defined by the pavilion, or bottom part of the diamond, that has a "scissor cut" with all facets step-cut down toward the culet, or point on the bottom. The blocked corners add to its geometric appeal, making the diamond appear almost octagonal. It is usually cut to a square outline as opposed to rectangular. This diamond shape is beautiful in a simple solitaire or in a setting that has simple geometric lines or side stones such as baguettes. Ideally, the setting for an Asscher cut should not hide the unique blocked corners.


  Radiant Shape Diamond

The radiant cut is a beautiful combination of the classic emerald cut and the sparkle of the round brilliant. The radiant cut is similar to the princess cut but is usually (though not always) a more rectangular outline and has blocked corners like those of an emerald cut. The cutting is a combination of the step-cutting of the emerald-cut diamond with some triangular faceting of the brilliant cut. The radiant cut is dramatic as a solitaire but also looks great paired with side stones such as baguettes, trillions, or princess shapes. A radiant-cut stone should be set with special prongs to hold the blocked corners securely.

 
 
      Cushion Shape Diamond
 
The cushion cut is an unusual diamond shape and an interesting alternative to an oval- or princess-cut diamond. Because these are relatively rare, this shape is for someone who wants something few people possess. The modern cushion shape is based on an antique cushion cut, which is a combination of round and square outline with a softened square or "pillow" shape. A cushion-cut may be squarer with length and width in equal proportion, or may have a slightly elongated outline, depending on the individual stone and the wearer's preference. As a solitaire, it makes a statement and also looks wonderful paired with side stones such as baguettes. A cushion-cut diamond setting should have at least four secure prongs.
    
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