Scintillation
When light reflects from a diamond, the sparkling flashes that come from the facets of the gem are known as scintillation.

Shallow cut
Cut refers to the angles and proportions a skilled craftsman creates in transforming a rough diamond into a finished diamond. When a diamond is cut too shallow, it will lose or leak light through the side or bottom. This results in less brilliance and value.

Shape
Shape refers to form or appearance of a diamond - i.e. whether the diamond is round, triangular, square, marquise, pear, oval or heart-shaped.

Step-cut
The step cut has rows of facets that resemble the steps of a staircase. The emerald cut and the baguette are examples of the step cut.

Symmetry
A diamond's symmetry is the arrangement of the facets and finished angles, created by the diamond cutter. Excellent symmetry of a well-cut and well-proportioned diamond can have a great effect on the diamond's brilliance and fire. Grading reports will often state the diamond's symmetry in terms Excellent, Very good, Good, Fair, or Poor.

Table facet
This is the largest facet of a diamond. It is located on the top of the diamond. The table facet is sometimes referred to as the "face."

Table spread
Term used to describe the width of the table facet, often expressed as a percentage of the total width of the stone.

Tension setting
A tension-set diamond is held in place by the pressure of the band's metal, which is designed to "squeeze" the stone.

Tolkowsky, Marcel
In 1919 Marcel Tolkowsky calculated the best theoretical compromise for the cut of a diamond to release the most beauty. The width of the table facet was found to be 53% of the total width of the stone, with a pavilion angle of 40 degrees and 45 degrees. The Tolkowsky cut provides the basis for the modern American cut.