Here are some links I found very helpful after purchasing an Innovation Marbling Boku Undo Suminagashi kit at Dick Blick (no compensation for that ad).
The master at work: https://www.youtube.com/watch?v=9nAez1H9iAwhttp://www.ruthbleakley.com/blog/2013/11/suminagashi-marbling-tips/
Copperplate paper took the pigment the best, rice paper works, coated papers do not. A white enameled tray worked better than plastic or aluminum for me, especially since it was not first washed in soap. Select a tray just slightly bigger than your paper. Card sized pieces are easy to start with. Using a tiny amount of dish soap and water mixed with my pigment gave me the best spreading without sinking pigment.
I would like to try this on fabric next! Cause I need another craft! No, I really don't. It's taking great discipline to finish the quilting project I'm in the midst of because this sumi printing is so fun!