[Unclenick]

Austenitic stainless steels don't attract a magnet. Other grades have enough chrome an nickel that they don't attract a magnet as well as carbon steel, so you can use a magnet to compare the two. Otherwise, if it has no finish, you will find acid acts a good deal more slowly on stainless than on regular carbon steel. It shouldn't have any rusty fingerprints on it, either. A good test liquid would be a rust bluing solution. It will raise fine rust over a day on conventional carbon steels, but not on stainless in any significant degree.