I float hand-ground sumi ink on water and have other clear mixtures (ox gall, soapy water, etc.) which I apply to the surface of the water with small brushes. Mulberry paper is laid on the surface to capture the pattern I have created. I then scan these monoprints at a high resolution and continue working on them in Photoshop.
I enjoy the practice of suminagashi because of the stillness of water, the trance like state you can work yourself into alternating ink and spreading liquid, looking for the pattern you want to capture. It is quiet, simple, and gives quick results that allow for easy experimentation.