The emerald cut is categorized as a stepped cut which means that the pavilion, the flat top and the cut sides down to the widest part of the cut, are cut in rectangular facets. This makes a larger flat area which highlights the clarity of the stone. For this reason, this cut is reserved for stones of the best clarity. The shape is rectangular, and for the classic emerald cut, the ratio of length to width is between 1.30 and 1.40 but you can choose a wider or narrower stone to accent the finger or setting better. The same cut in a square shape is called Asscher.
More Elegant Than Round
The emerald cut was developed to bring out the color and beauty of emeralds. Before long, people realized that other stones would also be enhanced by this type of cut. In the case of the diamond, the longer lines of the stone results in less fire than the round brilliant cut. It however, brings out more dramatic flashes of light. An emerald cut engagement ring may seem more elegant than the round cuts.
Because the stone itself is displayed without excess flair, it is important that the diamond for an emerald cut engagement ring be of the highest quality. Any flaws or inclusions will be more exposed and the flash is more dependent on the clarity of the stone than on the cuts. While many couples look for tradition at this special time, traditional cuts are more in demand and therefore, cost more.
An emerald cut engagement ring actually costs less than a ring with a diamond of the same size and quality cut in the round brilliant or princess cut. The emerald cut calls for a four prong setting is striking as a solitaire or flanked by smaller stones.
Source : http://www.weddingringsweb.com/the-beauty-of-an-emerald-cut-engagement-ring.html
