Good to know about the metal - they're sandblasting metal, and most of it is steel, so there will probably be some very fine pieces in it (dust like particles). The slag itself is made from iron ore, a by product of the ore refining process. I'm thinking it must be similar to sand, but made from something other than silica. Hmm. Testing. The particles won't be very small, and I will probably sift it to get really fine particles out. Apparently, you can no longer use silica for sandblasting, so he's now doing researching the life expectancy of a sandblaster who uses black abrasive slag instead. Only half kidding...
