Cracked marbles are really fun and easy to make and are always a crowd pleaser. I have found that the marbles that look like cat eyes work best and have the most dramatic looking results. Simply bake the marbles in an oven proof dish at 350 degrees for approximately ten minutes. You want the marbles to be super hot. While they are baking, fill a stainless steel mixing bowl with ice and water. Remove the hot marbles from the oven. You may want to consider eye protection for safety, the marbles will crack. Using tongs drop the hot marbles in the ice water. Once the ice water has completely cooled you can remove your beautiful cracked marbles. If you want to turn science into art you can use your marbles in jewelry or in a vase with fresh flowers.
Now to the science behind this experiment. For starters, glass is not a great conductor of heat. The outside of the marbles cools immediately and tries to shrink. In contrast, the inside of the marble is still hot and expanded. The marble undergoes “thermal shock” because the inside can’t compensate to keep up with the outside. As a result the marbles crack.