i have vapor blasted them with good results. a tiny bit brighter than OE but it fades in time. you could try a #10-ish glass bead as well. with aluminum, oils and contaminants will stain the metal. i do lots of aluminum resto stuff for customers on vintage bikes and anything that has oil cooked on will end up a different color than the part that was covered with paint or untouched so it needs to be made one uniform color before you can finish. all depends on how crazy you want to get