Polish is an important factor in grading of loose diamonds. The grading system for polis is set by the Gemological Institute of America (GIA.) The system is fairly simplistic. Loose diamonds have polish that is either excellent, or very good, or good, or fair or poor. If the loose diamond has a poor rating for its polish that means that it could reduce the intensity of any light that is reflected into or out of, or from, that loose diamond. The way gemology labs assess the polish of loose diamonds is to examine the diamonds minutely, looking at each facet separately. They do this by studying the reflected light the loose diamonds create when placed under a microscope.
Polish, just like the symmetry of loose diamonds, has become quite important in the diamond market because it appears on the gemologist’s report and also because there is no standard for grade of cut by GIA. The most common defect of the polish of loose diamonds consists of grain lines on its surface. Even highly skilled cutters can come across variations in how hard or grainy the surfaces of the loose diamonds are as they are polishing the diamond’s facet. This is similar to what happens when working with wood. The result of this is a miniscule polish line that runs across a facet of a diamond. These lines of grain happen often in diamonds that are fancy and pink, although it’s seldom possible to even see them except when they are in reflected light.
If a buyer chooses loose diamonds that have inclusions rated SI or VS it probably won’t matter that they have a few microscopic size polish lines. If one is seeking a flawless diamond, however, excellent polish is going to be of paramount importance. Any loose diamonds that have polish ratings of fair or poor will have visual performances that are noticeably less attractive than those with the higher ratings for polish.
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