Cut cardboard tube to the size you want the chalk to be.

Completely seal one end of tube with duct tape.

Line the tubes with wax paper and stand upright in a wax paper lined plastic container. The container you use might get ruined, so choose accordingly.

In separate bowls for each color of chalk, combine 2 tablespoons tempera paint and 1/4 cup cold water for each desired color.

Working with only one color at a time, add 1/2 cup plaster of paris and mix until thoroughly combined.

Spoon into the prepared tube and gently tap the tube on the table to remove air bubbles.

Repeat with all colors.

Allow chalk to set for 2 hours before peeling away all layers of the the tube.

For best experience, allow chalk to cure for 1-3 days before using. But you can use it right away too, if you can't wait!