As part of my unit on traditional art forms I thought I'd introduce my students to bookbinding, and the part that decorative paper plays in it. I started by handing them each a book and having them point to the front, the back, the spine, the head, the foot, the endpages. I showed them a book, mid-binding to show them what a signature was, a text block, let them feel uncovered book board. We looked at various hand-bound books: pamphlet books, link stitched books, accordian books, book boxes, and portfolios. THEN we talked about types of books: novels, poetry books, dictionaries, alphabet books, comic books, quote books, journals, sketch books, autograph books, pop-up books, the more you discuss it, the more types you remember. I showed them books I have that use marbled paper. Then we were ready to marble paper, and within the hour lesson, 4-5 kids had a completed project.
The idea of viscosity is really important in this process. The water must be thicker than the paint in order for the paint to sit on top. There must be a thickening agent such as starch or a little geletin for it to work. I got a kit from Dick Blick that had a powder called "water thickener." The hotter the water the better when whisking in the powder, and it's better to add it little by little is better than plopping in a couple stable spoons, as we soon found with too many lumps. You'll want to wait half an hour before using also. Which is why my first period started with this (calculating, measuring, mixing) before our book discussion. The paper must also be prepped by sponging it with a water and addisive powder also found in the kit. Be sure to do this at least 30 minutes ahead as well. I had students each class period prepare paper for the following period. Pay it forward and it saves everyone time.
Finally the fun part! Choosing and placing colors is an interesting process. Each little drop expands quickly and takes over the majority of the water. It's a good idea to start with the light colors, but patterns of dark and light also work well. We liked to create dots in concentric circles to make bullseyes because they make twice the lines when it comes time to swirl them. Long lines inside of lines works really well too. It's important not to squeeze too much paint at a time, because it will all sink to the bottom.
Swirling is even more satisfying than dropping the paint in the water. We combed through the circles trying to keep the teeth moving perpendicular to any lines that needed crossing. This is what gives it a nice marbled effect. Some students moved to quickly and things got a little messy, but most enjoyed the process. Once the swirls are how you'll want to catch them quickly by placing your paper, treated side down on top of the water. (I tried to put an X on the back side of paper before treating it because once they dry it's hard to remember what side was treated. It's also important to write student names on the back of the paper before marbeling because it will be to wet to write immediately following and lots of students can make lots of paper pretty quickly and get confusing later on).
You can use knives and forks, or combs that you find around the house, or you can make your own combs. We stuck bamboo skewers into cardboard at different spacings for different effects. A piece of tape keeps them from sliding up and down through the corrugations.
Then comes the most exciting part. Pulling the paper out of the water. There were always gasps and oo's and ahhhs during this part. If you're making a lot, you'll probably want to use latext gloves. Drain off the excess, and you can lay it down face up for a minute or two before gently rinsing off the extra sizing under a thin stream of water. It feels slimy from all of the starch so try to get off the excess without power-blasting it. Holding the paper with the water running down like a waterfall is better than holding it flat. You don't want to get the back too wet because most paper will get soggy and start falling apart.
It was fun to see the choices of color that students used. Some only choose two colors (like blue and white) while others wanted to do every color a bunch of times.
We experimented using colored paper, and it was fun to see how the paint colors came out differently depending on the under color.
A couple students opted out of combing and swirling their paint at all and that made for some fun images as well.
Ultimately, this assignment had a big "wow" factor and my students became so obsessed with making marbled paper that I had other teachers telling me that they were hearing about it in their classrooms. We covered ELA (books), science (viscosity), math (measuring, doubling, ratios), and Art within the matter of an hour before letting students play with their own ideas for the next few class periods. It only took me 13 years to try this out, but we may have to do it again some time.
With the right side up, push in on opposite diagonals until a square (1/4th of the paper size) is formed and push down. Keep the open side pointed towards you on the table. 
