Equipment

• Ice cube trays or small molds
• Mixing bowl or container (disposable or one you don’t mind ruining)
• Spoon or stirring stick

Materials

• 1 cup Plaster of Paris
• 1/2 cup water
• 2 tablespoons glow-in-the-dark paint
• Petroleum jelly or spray oil

Instructions

1. In a bowl, mix 1 cup of Plaster of Paris with 1/2 cup of water. Stir until smooth.
2. Add 2 tablespoons (or a few squirts) of glow-in-the-dark paint to the mixture. Stir well to combine.
3. Lightly coat the inside of your molds with a thin layer of petroleum jelly or spray oil to prevent sticking.
4. Pour the chalk mixture into the molds, smoothing the tops if needed.
5. Let the molds sit overnight to harden completely.
6. Once dry, gently remove the chalk from the molds. If they are difficult to remove, place the molds in the freezer for 15-20 minutes to loosen.
7. Before using, activate the glow by placing the chalk under a bright light for a few minutes.

Notes and Variations

• Use different shapes of molds, like stars or hearts, for added fun.
• For a multicolored effect, divide the mixture into separate bowls and add different paint colors. Layer them in the mold.
• Use gloves to protect hands while handling the Plaster of Paris, as it can be drying to the skin.
• Make sure the activity is supervised to avoid accidental ingestion of materials.
• Test the chalk on a small area of the sidewalk beforehand to ensure it glows well and washes off easily.

For more information, see https://young-catholics.com/1536/glow-in-the-dark-sidewalk-chalk/