the only school training i've had in welding was in high school. In my shop class all we learned was stick and o/a welding/cutting. In the course we didn't cover mig or tig so i'm curious all the purposes of shielding gases. I've picked up different gases and mixes will give hotter spark. I understand (shielding) gas keeps atmosphere off the weld/electrode. Really my question what does gas shield against.