A diamond’s brilliance is largely determined by its cut. An expertly cut diamond with perfectly symmetrical and aligned facets will maximise sparkle. This is because it reflects light internally from one mirror-like facet to another, dispersing it through its uppermost surface, referred to as the table.
Technical expertise and artistry are required to create perfect proportions. Too flat a cut dulls the diamond, with light leaking from the bottom, whereas if it is cut too deep, a dark point can appear within it as light escapes sideways.
While the cut is the only one of the 4Cs that isn’t determined by nature, it’s potentially the most important, such is its impact on brilliance and sparkle. This is why it’s possible for a well cut diamond to command a higher value than one that is slightly larger or of a rarer colour.