Cut and shape are probably the most confusing aspects of a diamond's quality and value. Diamonds of the same Color, Clarity, and Carat weight can have a difference of up to 40% in value depending on the cut and shape of the stone.
The shape of the diamond refers to the overall appearance of the stone, i.e., the geometric shape of the stone. Some of the most popular shapes are:
Round Brilliant Cut
Round outward appearance with kite and triangle shaped facets radiating from center to the girdle (brilliant facet arrangement). Most brilliant, most popular, and most valuable.
Princess Brilliant Cut
Square or rectangular outward appearance; brilliant facet arrangement. Second most popular, lends it self to modern or contemporary designs.
Canoe or football shaped outward appearance with brilliant facet arrangement. Also known as the Navette.
Mostly rectangular outline, can also be square, rows of parallel facets, and diagonally cut corners. Classic and traditional.
Oval Brilliant Cut
Oval or elliptical outline with brilliant facet arrangement.
Pear Brilliant Cut
Pear or tear drop outline with brilliant facet arrangement.
Radiant Brilliant Cut
Rectangular or square outline, with 70 kite and triangle shaped facets.
Heart Brilliant Cut
Heart shaped outline with brilliant facet arrangement.
Trilliant Brilliant Cut
Triangular outline with brilliant facet arrangement. Sold mostly as matched pairs for accent stones.
The cut of a diamond refers to how symmetrical and proportional the facets are arranged on the stone. The skill and accuracy the cutter uses in placing these facets at their correct angles and percentages is crucial for the return of maximum light to the eye.
A Round Brilliant Cut, being a symmetrical sphere, is the best example of how to demonstrate the effect light has on the cut. White light, when entering a diamond, is refracted and then reflected from the bottom (pavilion facets) and returned through the top (crown) of the diamond. Because of a diamond's extraordinary ability to break white light, what the human eye actually sees is an array of vivid spectral colors that is known as "dispersion" or fire. Another attribute of a diamond is hardness. Hardness gives a diamond an unsurpassed adamantine luster, which allows diamonds to reflect more white light (brilliancy) than any other gemstone. What the eye ultimately sees when an ideally cut diamond is viewed in light is a spectacular combination of dispersion (fire), brilliancy (flashes of white light returning from internal facets), and scintillation (flashes of white light returning from the surface).
When a diamond is cut too shallow, much of the light is lost through the bottom and not returned to the eye. This "windowing" effect tends to make the diamond lifeless and somewhat glassy in appearance. On the other hand, on a diamond that is cut too deep, much of the light is reflected out of the opposite side of the bottom of the pavilion. This tends to make the diamond appear dark in the center and provides little light return.
In 1919 a mathematician, whom also had an interest in diamonds, wrote a doctoral thesis outlining the proper proportions for maximum light return within a round brilliant cut diamond. Marcel Tolkowsky devised, mathematically, the cut parameters that would produce the maximum light return with a balance of brilliance and dispersion. Diamonds cut to his calculations are termed as an "ideal cut" or a "Tolkowsky-Ideal cut". Unfortunately, due to the weight loss in a diamond cut to these standards, most diamonds on today's market are not cut exactly to these specifications.
Fancy shapes are any other shape than Round. Being irregular in shape, these stones do not have a model for ideal proportions as do round stones. Fancy shapes are judged on the length to width ratio of the stone and then on the amount of 'bow tie" (optical effect created with the loss of light through the bottom of the stone). Here are some basic guidelines to follow for each particular shape.