Post-Burn Interior Scale
I've been reading the UDS thread for several weeks and I'm well on my way to completing a UDS of my own. One thing I'm running into right now is a black layer, almost metal scale-like, inside of my drums after the burn out. The first time I noticed it was after burning out a used chocolate drum with a thin copper colored liner that was easily removed with a few strokes of 180 grit by hand (very thin liner). I got concerned when I was having such difficulty removing it with a wire brush and 60 grit sandpaper after a 4-hour intense burn. I thought it may be galvanized with a liner over it to make it food-grade or something erotic from overseas (wasn't sure, so I didn't want to use it).
I decided to go with an brand new open head unlined drum through a local vendor I've worked with in the past. I burned the unlined drum to remove the rust-inhibitor coating, started sanding the inside to clean up the char, and noticed the back scale inside again. I've read hours of postings on other forums and have searched the UDS thread and haven't seen anyone address this yet.
How clean does the inside actually look after the burn? Some of the pics look extremely clean, some do not. I was extremely surprised to see the black scale again, it appears to look like another layer of paint but I think its just the burning process and oxygen reaction causing scale. Before I kill myself trying to remove this enigma, does anyone have any thoughts.