He mainly uses elephant hide, which is a kind of paper used in book binding - very durable and pliable, but only come in a few colors, most of them very boring (some, downright ugly).
I'm always on the look out for techniques I can adapt to make the papers more interesting.
Now, with no further ado, let's talk about this other technique I found - marble paper using the suminagashi technique. This one I didn't actually pin when I first saw it, as I didn't have the materials and thought I wouldn't be able to try it without buying the proper kit.

The image on the right is the enhanced version of what I actually got. I posted it here to show that the technique really works, albeit, in my case the colors were very light.
I knew that the technique relies on surface tension, I just didn't know how to make it work - i.e. make the paint particles remain suspended on top of the water until I put the paper on top of it.
I put some water (maybe a finger or so deep) in a cake pan - note to self, next time use a light colored container - and using brushes, placed a few drops of the same concoction I had used for the bubble experiment in the water. It was a no-go. The paint sunk to the bottom (why I expected it to float is beyond me. Soap breaks down surface tension...).

This time, to my surprise it did work. I could see the colors spreading on the surface, so I proceeded to do the "printing".
The image on the left shows the true colors. I think the reason I got such faint colors has to do with the amount of pigment in the paints I used.
I'll get some watercolors in both tubes and pans next time I got to the craft store in town and see if those work better. The idea is that with those I can add as much pigment I need, which would yield better results when doing the marble paper.
I consider this experiment to be successful because I did get the result I was hoping, despite the fact that the colors are washed out.