Many
jewelers don’t know the difference between a diamond’s cutting style
and the actual quality of a diamond’s cut. Jewelers often refer to a
diamond’s cut grade as the cut, although one has nothing to do with the
other.
Popular diamond shapes include Round, Princess, Radiant, Pear, Marquise, Oval, Emerald, Heart, and the Royal Asscher. Currently, the most popular shapes seem to be, in order: Round Brilliant, Princess, and the Radiant.
The cut grade of a diamond
is the physical measurement and relative proportion of a polished
diamond and is the most important characteristic in producing a
diamond’s beauty. A single number does not define cut; it is
a combination of measurements, relative percentages, angles, finish,
and performance of light within the diamond, all culminating in the
overall visual appearance.
The Four C’s; Carat Weight, Cut, Color,
and Clarity, have actually been around since GIA coined the term in the
1930s. AGS Labs only began grading a diamond’s cut quality in 1996.
Shape refers to the outline of the diamond as is the case in the round part
of a Round Brilliant. Asscher and Princess cut diamonds are modified
squares while Emerald and Radiant cuts are more rectangular. The best
way to judge shape appeal is to look at a diamond’s girdle or outline
and decide if it’s attractive to you. The most indicative aspect on a
grading report that will determine how a fancy shape will look is the
diamond’s length divided by its width, called the length to width ratio.
The wholesale price list used by almost every diamond jeweler and major retailer around the world (published monthly and known as the "Rapaport Diamond Report") gives prices for four shapes: rounds, emeralds, pears and marquise shapes. The charts for pear shapes are used for all other shapes. The prices given vary by shape, for two reasons, but mostly due to the popularity of each shape, which creates the demand. Prices go up when demand goes up.
The other reason is more technical and has to do with the cost of the rough diamond (called "rough" for short) and how close it is to the final shape the cutter can achieve with it. The size of the diamond the cutter gets is called the yield. When the shape of the rough is very close to the shape of the finished, the cutter doesn't waste as much, meaning the yield is high. That means less of the diamond is ground into dust on the cutters table, and more of it is sent out to sell. The higher the yield, the less waste, and the better the price. Generally speaking, rounds are a good yield, about 53% or so. But princess cuts are better yields because they are closer to the natural double pyramid shape of the rough (the octahedron), making the yield for a princess cut about 55-60%, and making them better deals in most cases. That is why princess cuts (as well as radiants and emeralds) are priced lower than rounds in most cases.
The cutting style refers to the angles and proportions of a diamond and has nothing to do
with its shape. It is the facet arrangement like the brilliant
part of a Round Brilliant, Modified Brilliant (Princess), or the steps
in an Emerald or Asscher. Fancy shapes contain pavilions that are made
up of varieties of angles due to variance in length and width.
Light
performance in fancy shapes is much more complex than in rounds. A
diamond’s dimensions, polish, and symmetry can’t be relied upon to
determine how well these shapes will look. It’s even possible to have a
fancy shape with a table larger than its total depth and return the
maximum amount of light as possible. At Fire & Ice we, however,
know how to manipulate and align facets in a way that maximizes light
performance.
 Step cuts are carvings in a diamond almost like a stairway. This is how Emerald
and Asscher cuts are created. These diamonds have an elegant simplicity
reminiscent of vintage and antique rings, and although they should not
sparkle as much as brilliants, the elongated surface of the stone
presents a majestic appearance. The downside is that flaws and other
defects are much more visible to the naked eye.
 Brilliant cuts are
called so because they are designed to perfectly balance brilliance or
white light return with fire or colored light. It is the vertical
direction crown and pavilion facets like the sides of a pyramid,
instead of step style horizontal facets. These cuts are intended to
maximize facets in a diamond at certain angles for internal refraction,
resulting in maximum light return instead of reflecting off the
diamond’s surface, like a mirror. Almost all cuts fall in this category.
Mixed-cuts are a combination of the two in order to maximize appearance as is the case with the Radiant cut.
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