Hello. In my science class we had fun with steel wool and vinegar. So just for kicks I left the remains in a closed jar and shook it up every few days or so. Its been around 6 months and today I opened it just to see what was in there since the entire jar was pitch black. Inside was a dark silver mush that seems to be magnetic. I took some out of the closed jar to expose to the outside air to evaporate any remaining fluids and left it on a powerful magnet. What was left over was a dark magnetic, very fine caked powder. What exactly is it? Can this powder be introduced to anything to make a homemade version of ferro fluid? Thank ya kindly.