Dust and chunks that burn and cannot be put out.
Yeah, I thought about playing with that once in my life. I had a dead house furnace many years ago. I documented it on the board of course.
I helped the guy take it out and before we took it out of my basement he beat the hell out of it with a sledgehammer. He did it on top of a sheet and we turned the furnace while he did it.
When he was done there was a huge pile of rust. This is a 40-year-old furnace that has been rusting away in my damp basement.
So that meant I had a huge amount of iron oxide to work to create my own thermite. I held on to that for a couple of years before I realized how stupidly dangerous this was and I had no business touching it.