Here are some more samples of fabric I rusted. When I first tried years ago when the concept was new to fiberart, I didn't have much luck.
Thanks to the internet, I found a way to do it that works for me. The fabric has the soapless scouring pads put on it, sprayed with vinegar, and wrapped in cling film/plastic wrap. It only takes an hour or two to work. Then the metal is thrown away, and the fabric washed.
The hard part is finding the soapless scouring pad that isn't treated so it doesn't rust! The other thing to watch out for is not cutting yourself on it when you cut and pull it apart to layer it on the fabric.