Though extremely difficult to analyze, the cut of a diamond has three attributes: brightness (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the light flashes – or sparkle – when a diamond moves).
An understanding of diamond cut begins with the shape of a diamond, with the standard round brilliant dominating the majority of diamond jewelry. All other diamond shapes are known as fancy shapes or fancy cuts and include the marquise, pear, oval, and emerald cuts. Hearts, cushions, triangles, and a variety of other new shapes are also gaining popularity in many forms of diamond jewelry.
As a value factor, though, cut refers to a diamond’s proportions, symmetry, and polish. For example, look at a side view of the standard round brilliant. The major components, from top to bottom, are the crown, the girdle, and the pavilion. A round brilliant cut diamond can have either 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion, known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle, and pavilion depth. A wide range of proportion combinations are possible, and these ultimately affect the stone’s synchronicity with light.
In early 2005, GIA unveiled a diamond cut grading system for standard round brilliants in the D-to-Z color range. This system, the product of more than 15 years of intensive research and testing, assigns an overall diamond cut grade ranging from Excellent to Poor.