I needed some rusted chains for a costume im working on. unfortunately lowes doesnt sell rusted chains so i found some really heavy duty chain for $2.27 a foot. if you soak the chains in a vinegar soak over night followed by a salt water soak the next night when you leave them to sit out they will rust in just a few days. spraying them with water periodicly (spelling) will speed it up.
the longer you leave it in the vinegar the more rust will be formed. i left it just over night and it started getting spots all over where it had begun. it also doesnt matter what kind of vinegar i used a mix of this red vinegar and balsamic and it worked very well (smelled awful though).
so far its worked very well and im pretty sure from what i was told it will work on any metal. gives it a real rust and works very well so far. will post pics soon!