I've been meaning to try rusting things for awhile now. I finally gave it a go. Before I move on I have to say-the cheaper your metal, the better. If you can find bells from the dollar store....grab them. If you can pick them up with a magnet-that's a good thing. If not, they have a coating that is going to be a booger to get off. The same things applies to metal pieces like safety pins that you might want to rust. Second, the longer you soak them, the more rust your item with acquire. After the first few days the brown 'stuff' with be floating around your bucket, but it takes awhile to start adhering to the item.
All you need is vinegar, hydrogen peroxide, and salt. I covered my items with vinegar and let them soak for about three days. I dumped out my vinegar and then I covered them with the hydrogen p and I added about 1/4 cup of salt. I let THIS soak for over a week. The second step is when the rust started forming. It may not take as long with cheaper metal, but I learned the hard way.
When you pull your items out, let them dry on a newspaper for a few years so the rust 'sets' on the item. If you are going to keep your item out in the weather, you might spray them with a coat of clear spray to make sure they stay rusted.