How to polish porcelain?
Remember, porcelain isn't a polished smooth surface, it's a glazed sprayed on surface that's then fired at about 2300 degrees F. Once you've smoothed out the edge fill in any cracks or damaged areas with an epoxy glue. Let the glue self settle so it's a smooth surface and don't over apply. As far as matching the color, try nail polish. it comes in hundreds of colors and does a great job of sealing and self leveling for a smooth surface. I repaired a chip on a toilet and this really works well. Good luck