Aluminum comes coated with a very thin clear film. It can be burned through when TIG welding, because of the cleaning effect generated by the AC welding process. It can also be MIG welded without removing the coating, but sanding it is a help. As for oxidation, anything that is not pure aluminum will not weld. Paint, oxidation, JB Weld, anything that is not aluminum, has to be removed. The flash is brighter than any other metal. It welds much faster than any other metal too. You have to move quick. The TIG rod melts much faster, and when aluminum melts, it turns into a thin liquid, almost like water. Where steel puddles together, Aluminum doesnt do that. It does make more smoke, than steel, but my welding booth is about 15x15 feet, and a small exhaust fan handles the smoke with no problem. No need for a mask of any kind, unless I grind.