Water marbling is an easy way to explore art and science! Start with
Glue, like Elmer's Glue
Tempera or acrylic paint - start with 1-2 colors
Toothpick or a butter knife
Paper, the thicker the better
Check out the how-to in this video:
By thinning down the acrylic paint you make it less dense than the glue. When you gently pour the paint onto the glue it floats on top because of the difference density. If your paint sinks to the bottom in the glue and water solution, add more water to thin it out. When the paper comes in contact with the paint, the water and paint mixture is pulled up into the tiny spaces between the paper fibers in a process called capillary action.