Baked marbles! Bake the marbles on a cookie sheet at about 325 - 350 for 20 minutes, as soon as you take them out of the oven put them in a metal bowl or sink of cold water and ice & they'll crack, but just on the inside.
Best science experiment ever! Make a fatastic eruption with hydrogen peroxide, yeast, soap, and food coloring! Perfect for science shows for all ages: preschool, kindergarten, elementary, middle, and high school! Even adults enjoy this one!