Another option than anodizing is to spray the polished portions of the grille with a clear ceramic coating. I don't do a ton of polishing and buffing here but when I do, I use MC-160 Cerakote (NICindusries.com) to seal, protect and keep it from oxidizing. Over the last couple of years it has completely replaced the clear powder coating I used to use on my HP273 Commando valve cover restorations and other polished aluminum parts. The site won't let me add any photos here (grrrrr) but there are tons on my website http://PhoenixSpecialtyCoatings.com, FaceBook and Instagram @cudachick1968.