The first two photos are the back and front of the cotton, and I used a rusty saw blade that I found in the shed behind my house.The second two images are close ups of places on the fabric where there were more distinct images.Rust dyeing is really simple: take a piece of fabric, any kind will do, and soak for a little while in vinegar water, 50/50 would be good. Directions I've seen say you should use salt water for cotton and vinegar for silk, but I found the salt water didn't work as well on cotton. I'll stick with vinegar in future, regardless of type of fabric.
Then lay out the fabric on a piece of plastic, and place rusty junk wherever you want to, wrap the fabric around, wrap the plastic around the whole thing, and leave overnight or for a day. I worked this piece for five days, because I was trying different things, as I said above. I started with a beautiful piece of old rusty chain, pretty thick stuff, but found it didn't dye well because despite it's being so lovely, there wasn't much rusty surface area for the fabric to come in contact with. Then I tried a couple of rusty garden tools with long blades, which worked well. Then I found the saw blade and a fireplace tool set and tried all of those. Definitely flat stuff works best for covering larger areas with rust.
This morning, satisfied that I had as much rust on the fabric as I wanted for now, I steamed it for 20 minutes, then washed and dried it. Now I've got a half yard of interesting dyed cotton to do something else with!