Many people who buy diamond get confused between diamond cut and diamond shape mistaking a shape as type of cut. More often than not, buyers give more weight on the 3C's (Carat, Color and Clarity) and ignoring the crucial effect of the "4th C", the Cut grade.
A diamond cut greatly affects the sparkle of a diamond. It is how well a diamond is proportioned. It pertains to the symmetry or how symmetrical the diamond sections are. Symmetry & proportions are responsible in allowing a diamond to have a proper reflection of light entering from any direction to be totally reflected through the top and dispersed into a gorgeous display of color. If the symmetry, proportions and polish are made perfectly, the diamond will display an excellent sparkle and most likely be graded as "Ideal Cut Grade".
In the past, little importance was given to the quality of diamond cut and grading was mainly focused on color and clarity. But the beginning of the 20th century, when an optical brilliance was studied deeper, the forms of diamond cuts developed through trial and error. Year of 1910 came when the calculations had been applied where the physical and optical properties of a diamond such as dispersion, light refraction and hardness were highly considered for maximum brilliance through an accurate proportions and symmetry. Such style of cut underwent the longest and highest degree of development as it started long ago as the first century B.C, and only in the 20th century did it arrive in full maturity in the form of a round brilliant cut diamond.