Steel welding wire spool mystery?

I bought a used wire welder with a spool already installed, with a regulator, but no gas cylinder, and indications from the guy who sold it was that he wasn't using gas with it. The wire, though, is .025" and my pretty strong impression is that wire that small couldn't be flux core. The wire is off-color -- kind of brownish -- however, and I wonder if that could possibly be a flux coating. ? Doesn't look like rust and it's certainly not bronze or br wire. I can't contact the guy who sold it any more ... don't seem to have his contact info (wife deleted emails and he's not in the phone book). The sticker on the side of the spool isn't helpful at all. Anyone hazard a guess as to what material this is and whether or not I can use it without gas? Thanks for hints!!