The fourth and final C, Cut, refers to the diamond's proportions, symmetry, and polish. A well-cut diamond refracts light better, appearing more brilliant and fiery. A poorly cut diamond, on the other hand, can appear dull and lifeless. The cut grade ranges from Excellent to Poor, with various degrees of precision in between. The cut of a diamond is considered the most critical factor in determining its value, as it directly impacts its beauty and sparkle.