It's trial and error and a LOT of work. Best to get the right tools for the job also, I bought a strong buffer an ingersol rand die grinders strait , 90 degree, compound (from sears) and buffs. For best results clean very well,have many grits of sandpaper from 80 to 2000 grit and get ready for some sore arms and fingers., The better sanding job the better end result you will have. Here's the first set of valve covers i've done but don't have a pic of them after final polish was done.