I've always loved the look of decayed, rusty things - there's something beautiful in the unpredictability of the aging process.
You can buy kits now to rust objects, but it's really easy (and cheaper!) to do yourself. This technique works on both fabric and paper.
HOW TO GET RUST PRINTS ON PAPER/FABRIC
1. Cover your work surface to protect it - I've just used plastic sheets - and mix your rusting solution: 1 part white vinegar to 3 parts water.
2. Collect the metal objects you want to print with. A lot of modern metals are made not to rust so you may need to experiment. It's best to use pieces that are already showing some signs of decay - a lovely man at a local second hand market gave me some of these bits for free :-)
3. Saturate your paper/fabric with the vinegar/water solution and place the metal objects under or over it (if using fabric, this can also be wrapped around the objects).
4. Fairly flat objects will give clearer prints. Laying another sheet of plastic over the top and weighting it with a heavy book or similar will help give the fabric/paper good contact with the rusting objects.
5. Leave it alone for a while and let nature take it's course! If it's a nice day leaving it out in the sun can speed the process.
I've left these examples for a couple of hours. This is what I ended up with -
On tissue paper
On paper and crochet doilies
More tissue paper (right) and cartridge paper (left).
I also ended up with quite a nice rust print of the keys on the plastic I used underneath!
And here's an example of a rust printed key that I used in my artwork -
You can experiment with different objects/papers/fabrics and see what happens. I haven't yet tried this on printed papers but I think that will be my next experiment! Have fun :-)