First aluminum welds- nothing to write home about

[DaveO]

I thought I'd try the "pad" that Jody recommends, but it quickly became clear that I need to RTFM some more (and get more practice). Eventually I got around to some lap joints. What is the cause of the sooty looking coating on lap #3 at the bottom of the photo?

For the lap joints I scored a piece of 1/8" x 3" flat and broke off 1 x 3 pieces (roughly). The surfaces you see are all the underside of another weld, and all those pieces went from "shiny" aluminum to the brown discoloration. Is that overheating the base material? Controlling heat was a problem. The puddle would turn from fluid to ropy, and I was trying to recognize a pattern for what was causing it.