I started working with oatmeal as a resist about 5 years ago. It's a little more involved than flour paste, but it creates a very distinctive pattern. It is also very versatile. You can achieve vastly different patterns depending on the ratio of water to oatmeal, whether you let the oatmeal dry or not before handpainting and whether you handpaint or immerse. Below are photos of a few of my samples.
Oatmeal on silk
Hand painted while the oatmeal was still damp
Oatmeal applied with a spoon. Looks kind of like popcorn, doesn't it?
Immersed instead of hand painted. If you look closely you can see the paw prints where my cat
jumped up and did "the slide".