Diamond Symmetry & Polish
The symmetry of a diamond refers to the symmetrical alignment of facets, and plays an important role in the cut grading. Like cut, some gemmology labs start at Ideal, others Excellent. Fancy shaped diamonds have a symmetry grading.
Polish influences how well light is able to pass through a diamond and is very important to a diamond's brilliance. It is necessary to select a diamond that is laboratory certified with good, very good or excellent polish (some labs also grade "Ideal"). Diamonds that have poor to extremely poor polish are less brilliant because they have microscopic polish lines that blur the surface of the diamond. These polish lines reduce the amount of light that enters or exits a diamond.