Crackled Marbles

Lately, my five-year-old daughter has been obsessed with stones and all things sparkly and jewel-like. When organizing our art cabinet the other day, I found a bag of marbles. I remembered an experiment I did as a kid that I knew my little treasure-lover would enjoy: crackling marbles!


To do this fun, visual experiment, you will need:

  • Clear glass marbles (they can be all clear or have the rainbow swirl in them, but the opaque kind won’t show the effect.)
  • Heat: An oven-safe baking dish & your oven
  • Cold: A cup of ice water

I started by asking my daughter what she thought would happen to marbles if we baked them in our oven, and then put them into ice water. She thought they might melt in the oven and then freeze in the ice. Then, like a true scientist, my daughter decided to divide up the marbles into two sets – ones that would “stay uncooked” and ones that would “get cooked.” At the time, her rationale was that she didn’t want to “melt” all of our pretty marbles, but I couldn’t help but think that maybe she was innately creating a control group for the experiment, right? ☺



We preheated our oven to 500 degrees F, and we put the “get cooked” half of the marbles into an oven-safe small loaf pan. We baked the marbles for 20 minutes.

When it was time to carefully take them out of the oven, we had a large cup of ice water ready on the kitchen counter. I carefully lowered marbles into the cup of ice water using a small ladle. *Be cautious here: Glass can crack when its temperature changes quickly and drastically, so you might want to wear goggles and ask your child to do so. I’ve personally never seen this happen during this experiment, but be aware and have your kids stand back, just in case.

This experiment will demonstrate the effects of thermal shock on glass. Marbles expand all over, at relatively the same rate, when they are heated. However, when marbles are cooled off instantaneously, their outer layer cools first and shrinks. The inside is slower to cool, and therefore still expanded, forcing the insides to crack under pressure.

All of our marbles stayed intact this time, but I’ve seen some break in half during this process.

After observing the differences between the “cooked” marbles and the “uncooked” marbles, my daughter added these crackled marbles to her treasure chest and is using them as her pretend jewels and magic stones. Whether it’s science or magic (or perhaps a bit of both in a child’s eyes,) marbles that have undergone thermal shock really are lovely, sparkly orbs!


Guest post by Jen Berlingo, MA, an art psychotherapist and blogger over at



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