The charcoal addition is so you don't burn out the carbon and by adding it you can stop worrying about burning it out with a higher welding heat. That's all I meant to do with it. Maybe if you can burn hotter it may weld better. It's just something in a YouTube video, I think it was one of James McClendon's videos. May have been somebody else, was it you James?
Found it at the end of this video. Yep, it's James.
https://www.youtube.com/watch?v=DQFsHhfdlPs