The diamond cut is the most important characteristic which influences the diamond's beauty.
There is Cut. And then there's Cut.
It is the cut that enables a diamond to make the best use of light.
1. When a diamond is cut too shallow, light leaks out of the bottom, brilliance is lost and the diamond appears water glassy and dark.
2. Light entering the diamond reflects internally from facet to facet and is reflected back through the top ONLY, creating maximum brilliance.
3. When a diamond is cut too deep, light leaks out of the bottom, brilliance is lost and the center of the diamond will appear to be dark.