What pradeep1 said. The stuff can be really harmful if you don't handle it properly. If you decide to use a NaOH solution to strip annodizing, I recommend you use thick gloves and serious eye protection (a loose apron over your clothes wouldn't hurt either) and work in a well ventilated area. If you want to learn more, here's a link to PEU's "Removing HA3 success" thread. Good info was posted there by members with lots of experience with anodizing.