Hmm.. any other tips to keep the material from getting scratched?

I have to ask since I never used it before, but can I tig weld aluminum (corner welds) with the pvc coating on, and just cut it back from the edge about 1/2-3/4"? trying to keep the scratches to a minimum.

I have a stupid newbie question, and I don't know why my teacher didn't discuss this, but what does the gas lens do exactly?