It's Rust Dyeing weather!!! It's incredibly easy to rust dye fabric for unique pieces of art cloth.
Plastic wrap or black trash bag
Lay objects onto your fabric, saturate with vinegar, cover with plastic and place your fabric in a warm, sunny location, like the roof of your garden shed, etc. for about 12 hours.
After 12 hours remove plastic from fabric piece, and check for marks left behind by the rusty objects. If the marks are not as intense as you'd like repeat the process. Otherwise your fabric is now ready to be rinsed and then washed.
To learn more about Rust Dyeing read my article here...
I placed my fabric into a rusty old wheel barrow and placed rusted objects on top of the cotton fabric. I then saturated the fabric with vinegar, covered the works with a piece of heavy plastic for 24 hours.