Things You'll Need
Molds (cardboard toilet paper tubes, small matchbox boxes or candy molds)
Tin vegetable can
Plaster of Paris
Tempera paint, optional
While blackboard chalk is pretty inexpensive, it is a lot of fun to make your own. When you make your own chalk you can use a variety of molds to form interesting shapes. Cardboard toilet paper cores, small matchboxes and candy molds make excellent choices for molding one-of-a-kind blackboard chalk. Use simple sachet bags to keep the chalk in and to hang next to your blackboard. This project is a quick process and with drying time, you can be writing on a blackboard the next day. Make several sets for your blackboard memo board or give as party favor gifts for your child's class.
Slice the length of a toilet paper tube with a craft knife. Overlap the edges and tightly roll the tube to form the size chalk mold you desire for a simple chalk stick. Tape the entire length of the seam with masking tape to seal. The cardboard molds can not be reusued, so repeat with additional toilet paper tubes. Stand the tubes in a tin vegetable can to prepare for molding.
Fill the Styrofoam cup 3/4 of the way full with water. Spoon heaping spoonfuls of Plaster of Paris into the cup and mix. Continue to add one spoonful of plaster at a time until your mixture is the consistency of watery pancake batter. Note: Use two plastic spoons, one for mixing and one for adding Plaster of Paris. If color is desired, add a few drops of tempera paint to the plaster mixture.
Squeeze the rim of the Styrofoam cup to form a pouring spout. Pour the plaster mixture into the cardboard toilet paper tube molds to form your blackboard chalk sticks. Lightly tap the can on your work surface to shake the plaster down into the molds and remove air bubbles. Fill the molds to the top and set aside.
Pour more plaster into the small cardboard matchbox boxes and candy molds. Tap the molds on your work surface to remove the air bubbles. Allow the blackboard chalk to dry overnight.
Pull the masking tape off of the cardboard tubes. Peel the cardboard from the chalk. Peel and tear the cardboard of the matchbox boxes to remove the chalk from the boxes. Slightly twist the candy mold to pop the chalk from the molds. Place sets of the blackboard chalk into sachet bags for gifts and storage.