Diamond guides
Diamond Cut
Cut is the only grade that is entirely human. It is also the one that does the most for how a stone actually looks.
What it is
The cutter's decision, not nature's
Color, clarity and carat are what nature produced. Cut is what the cutter chose to do with it — the angles and proportions that decide how light travels through the stone and back to your eye.
What it means for you
The last grade to give up
A well-cut stone one grade lower in color will outshine a poorly cut stone that grades better on paper, because a bad cut leaks light through the bottom instead of returning it. If you are trading grades against each other, this is the one to protect.
A caution
The top grades are not standardized
Laboratories and vendors word the best grades differently and the names do not line up. Excellent, Ideal and Super Ideal are each their own rung here rather than synonyms, so read a grade against the laboratory that issued it.
An overall cut grade is given to brilliant-cut diamonds. Step cuts such as emerald and Asscher, and colored stones generally, are not graded this way.