My buddy sat me down at his welding bench one day, and told me "You are going to learn to TIG aluminum right now, dammit!" 15 minutes later, I had lain down a very nice filet weld on 1/4" plate. Two days later, I noticed a burning sensation on my chest, and when I looked, it was red from just above my navel to my neck. WTF?? Then I noticed that it was a perfectly horizontal line across my belly. I had a nasty UV burn, right through the light shirt I was wearing, and the distinctive line was where the edge of the bench shielded my belly from the rays.