Thanks for checking out this week's FMF! We're talking about penetration this week and what are a few ways to know you're getting it. This is mainly focused on 1/8th inch aluminum because that's where the question came from! Enjoy!
Here's a video showing how the arc gap can affect your weld. You're looking for that Goldilocks Zone. If you're having issues with scummy looking welds and black pepper floating around in the puddle you might be holding too far of a gap!