Diamond polish influences how well light is able to pass through a diamond. It is a very important attribute in determining a diamond's overall brilliance. When choosing a diamond, it is best to pick one that is laboratory certified with good, very good or excellent polish. Diamonds with poor polish are significantly less brilliant because they have microscopic polish lines that blur the surface of the stone—this also reduces the amount of light that enters or exits the diamond. Be aware that many diamonds have a poor polish because some diamond cutters reduce their costs by not spending sufficient time to properly polish a diamond.
Polish is graded the same that way symmetry is graded. On a GIA report, the grades are Excellent, Very Good, Good, Fair or Poor. The same applies for AGS and IGI reports, which also include ideal in their list.
There is very little difference between these ratings to the unaided eye. A diamond with a polish rating of Good can still be a remarkable stone. It is only under magnification that the differences in these ratings become clearer. Polish rated Fair (FR) and Poor (PR), however, indicates that the flaws in the polish are visible to the naked eye and affect the overall beauty of the diamond.
It is also important that your ring does not have a porosity problem or rough spots in the metal. Porosity is when there are little surface holes that get worse as you go deeper into the metal. Generally the result of mass producing rings with poor quality control, porosity makes a ring weak and is non-repairable. A ring with porosity will eventually break down.