The way light passes through diamonds is influenced by the polish. A diamond’s overall brilliance is dependent on this important attribute. It is best to choose diamonds that are certified by laboratories with good, very good or excellent polish. The diamonds that are significantly less brilliant have poor polish because the surface of the stone is blurred by microscopic polish lines, thus reducing the amount of light that enters or exits the diamond. Because some diamond cutters want to reduce their costs, they don’t spend sufficient time to properly polish a diamond, thus resulting in a poor polish.
Polish and symmetry are similarly graded. GIA, AGS and IGI reports grade polish as Excellent, Very Good, Good, Fair or Poor but AGS and IGI also added Ideal to their list.
The naked eyes see very little difference between these ratings. A polish rating of Good can still mean the stone is remarkable. The differences are only noticeable under magnification. However, flaws that are visible to the naked eye affect the overall beauty of the diamond and put the diamond in the Fair (FR) and Poor (PR) category.