Cut vs Shape
Ok here’s where it gets tricky. While many people use these terms interchangeably, ‘cut’ and ‘shape’ actually mean totally different things. Diamond shape refers to the outline (rectangular, round, pear-shaped) of the diamond whereas cut relates to less obvious elements like proportion, facets, and polish.
So, even though diamond shapes have names like princess cut, emerald cut, round cut, and pear cut, those names are still referring to diamond shapes, not diamond cut. Not confusing at all, right!
How Cut Affects Sparkle
Sparkle is determined by a diamond’s ability to take in light, then reflect it back out to the spectator. The more light reflected through a diamond’s facets, the sparklier it will appear.
This is where cut comes in – a well cut diamond allows light to exit through the top, giving off a brilliant, multifaceted shine towards the spectator. Poorly cut diamonds, on the other hand, allow light to escape out the sides and bottom, creating a dull, lacklustre finish.
Diamond Cuts - Proportion
One of the most important factors of diamond cut is proportion. Proportion refers to the ratio between different sections of the diamond (see image below).
Gemologists measure these sections to help determine a diamond’s cut quality, and ultimately, it’s level of brilliance, fire, and sparkle. A well-cut diamond has the optimum ratio between the table, width, and depth to allow light to reflect out of the table (top) rather than out the sides or bottom.