that's good advice.. if you can take a couple of different metals to compare at the same time though.
You are probably referring to wrought iron. In addition to sparks, you can also sand it to a fine grit and then etch it for an hour or so in ferric chloride... which you get through electrical supply stores. Or try etching it vinegar or mustard. Just make sure it soaks long enough. Then look for linear etching patterns. From the side it looks like it is layered.
If you are equipped, heat it up to above non-magnetic and quench it. It won't harden even a little bit if its wrought.
Or.... send me a chunk.