Itajime shibori is the Japanese name for what we can simply call "fold and clamp". The cloth is folded and then part of it is clamped, on both sides of the fabric, with similar shapes of wood.
I found a nice set of wood shapes at Michaels Craft Store, ranging from round, to oval, to rectagular. They were made of 1/4 inch plywood - very sturdy for this process.
The following example of Itajime has been titled "Indigo Moons". I started with white cotton and prepared it using bomaki shibori. Then after one dip in the indigo vat, I let it oxidize and used my new round wood shapes to complete the itajime. After a second dip in indigo, I re-clamped it with a smaller round shape and dyed it one more time. I love the resulting patterns.