For this activity, you'll need to gather the following materials: baking soda, Liquid Watercolor® or food coloring, dish soap, vinegar, a glass jar, small plastic containers, a tray with a lip around the edge and heavy art paper.
Place a piece of art paper in a tray. Fill a jar halfway with vinegar and add a few drops of Liquid Watercolor. Squeeze in some dish soap and mix again.
Place the jar onto the paper in the tray. Then, have a child place a teaspoon of baking soda into the jar and stir the mixture together.
Stand back and watch the eruption! As the flow begins to slow down, you may add another color of Liquid Watercolor and little more baking soda for another colorful eruption.
Remove the paper from the tray, pour the foam off the paper and allow the paper to dry. Have the children use the paper as the background for a picture or to cut up into pieces for a collage.