I use Marblethix, which is a product I purchase from an art supply catalog. If this product is unavailable then you can use liquid starch. Pour into a container that is large enough to allow your paper to lie flat. I use a dishpan. Now softly drop your paint in so it floats on the surface. I have used tempera and acrylic with equal success. You need to thin your paint enough so the paint will float. You can swirl the colors with a comb or pencil. Lay your paper on the surface of your solution and pick up. The colors will "stick" to the paper!

Colored chalk can be scraped onto a pan of water and "lifted" with paper. While this technique does not give the "swirled" effect it is a nice alternative to the technique above.

Shaving cream and paint is another fun method. I use the cheapest white shaving cream I can find. Spread onto table and drip paint on the surface. Again, I have used tempera and acrylic with success. Swirl around with a comb to achieve the swirled marble effect. If you miss a spot you can lay your paper down again. Once you have covered the paper with color rinse the shaving cream off while still wet.