we learned that you need to handle all your parts with rubber gloves. Let them set up for 3-5 days before touching or installing them. The acidic grease from your fingers will cause the aluminum to permanently tarnish with your finger prints. We just did a full set of aluminum engine parts about a week ago using a #9 or #10 glass bead. The results were absolutely amazing. But you have to let the aluminum parts sit up for a bit. thats critical.