These sidewalk masterpieces are a fun, safe way for kids to get a taste of how artists have used the technique of painting into wet plaster for thousands of years.
Send your kids outside in old clothes to do this project on a sidewalk or driveway. Or, pour the cornstarch goo into containers for an indoor project. Frescoes can be washed away with a garden hose, but some food coloring may leave temporary marks on concrete.
To make cornstarch frescoes, you’ll need:
- 16 oz Corn starch
- 1 ½ Cup water
- Food coloring or watercolor paints
- Toothpicks or small paintbrushes
Directions for mixing the plaster, and making the frescoes:
1. Have your child measure the water into a large bowl and use their hands to mix in the cornstarch until it looks like glue. If the cornstarch goo is too dry and crumbly, add a little more water until the consistency seems right. You should be able to roll the goo into a ball, but it should drip like a liquid when you stop moving it around. Play with it!
2. Pour some cornstarch mixture onto a clean, flat spot on a driveway or sidewalk. Alternately, you can pour it into a tray or pie tin.
3. When the mixture has flattened out, let it sit for 5 or 10 minutes before you begin painting on it.
4. Using toothpicks and brushes, paint designs on the cornstarch mixture using food coloring or watercolor paints.
5. Let the frescoes dry and observe what happens to the color. When you’re finished, wash frescos off of driveways and sidewalks with a garden hose.
The Science Behind the Fun:
When you mix together cornstarch and water, you create what scientists call a non-Newtonian fluid, because it doesn’t behave the way you’d expect a fluid to behave. This cool concoction acts like a liquid when it’s at rest, but is more like a solid when you move it around. That’s why it drips through your fingers when you hold your hand still, but you can roll it into a ball.
When you use food coloring to paint on cornstarch goo, color molecules in the food coloring are absorbed into the cornstarch mixture, but they can’t travel very far since the cornstarch mixture is so thick.
Real frescoes are made by painting onto plaster made of sand, lime, and clay. Some frescos have lasted thousands of years because a chemical reaction between the fresco materials and carbon dioxide in the air traps the colors in limestone.
© Quarry Books, 2016/Outdoor Science Lab for Kids
Featured Photos Credit: Amber Procaccini © Quarry Books
You can find more experiments like this one at kitchenpantryscientist.com, and in my books Kitchen Science Lab for Kids (Quarry Books) and Outdoor Science Lab for Kids (Quarry Books).
