Don Guyot’s pamphlet Suminagashi, an Introduction to Paper Marbling is available from Colophon Book Arts Supply, which also has some great suminagashi supplies. This is filled with great information.
The Ultimate Marbling Handbook by Diane Maurer-Mathison has a very informative chapter on Suminagashi as well, with information on making double prints, among other things.
Add the information in all of these books together and you’ll get a pretty complete overview of most everything you’ll need to get started with you own experiments!
Other than that, there is the rare art book Suminagashi-Zome, a translation from Tokutaro Yagi’s Japanese instructions, published by the Heyeck Press in 1991. Unfortunately, it is a pretty expensive and hard to find tome. I’ve got my eyes peeled!
I’ve been experimenting with so many different things- types of paper, different inks, double dipping, printing on both sides… The list goes on! I’ll have to tell you results and what I think I’ve learned a bit later. In the meantime, the pieces pictured here are just a few examples of what I’ve done so far.