I bought this last year and tried it on when the pinched nerve in my lower back was a bit of a mess...so I'm not an xs anymore and only made my preexisting pain worse.  It has stayed in my drawer ever since.  I am pretty upset that there are some stains on it, and I do remember only noticing the ones on the inside, not the grubby ones on the outside.  The inside I think is rust, but no real idea about the outside as I only noticed them when I was getting ready to take some photos of the corset.

Steel boning, and seems well made outside of the stains.  I believe the fabric is a soft cotton canvas.