Over the clay shape, start laying strips of thin cotton and painting them with marine epoxy. Keep doing it until the whole shape is covered. When that dries, you can smooth it with a Dremel with drumsander.
That's what you see here, the covered and smoothed shape. It can be recoated with more epoxy or epoxy and filler to get a smoother and tougher skin. Here is the Logician, first coated with epoxy and filler, then the finished head.