Cut against form
Ok, this is where it gets difficult. While many people use these terms interchangeably, “cut” and “shape” actually mean completely different things. The diamond shape refers to the outline (rectangular, round, pear-shaped) of the diamond, while the cut refers to less obvious elements such as proportions, facets and polish.
Although diamond shapes have names like princess cut, emerald cut, round cut, and pear cut, those names still refer to diamond shapes, not diamond cut. Not at all confusing, right!
How cut affects the sparkle
The sparkle is determined by a diamond’s ability to absorb light and then reflect it back to the viewer. The more light that is reflected by the facets of a diamond, the more sparkling it appears.
This is where the cut comes into play – a well-cut diamond lets light escape through the top and gives the viewer a brilliant, multi-faceted shine. Poorly cut diamonds, on the other hand, allow light to escape on the sides and bottom and create a matt, lackluster finish.
Diamond cuts – proportion
One of the most important factors in diamond cutting is proportions. The proportion refers to the ratio between different sections of the diamond (see picture below).
Gemologists measure these sections to determine the cut quality of a diamond and ultimately its brilliance, fire and luster. A well-cut diamond has the optimal relationship between table, width and depth so that light is reflected from the table (above) and not from the sides or below.