To make a volcano with plaster of Paris, you will need the following materials: plaster of Paris, water, baking soda, vinegar, red food coloring, dish soap, cardboard and several small disposable cups. Build the volcano on a cookie sheet, or another surface that will contain any mess and allow easy cleanup.
First, make a cone shape out of the cardboard. Place a cup in the top of the cone; this forms the volcano's crater. Mix the plaster of Paris with water, following the instructions on the package. Use the plaster to cover the cardboard and form the volcano, but be careful not to get any plaster in the crater. Let the plaster dry completely. If you wish, you can decorate the volcano with paint, markers or other art supplies.
In a separate disposable cup, mix one-fourth cup vinegar with a small amount of dish soap and water. Add some red food coloring to achieve the desired color. Measure 1-teaspoon baking soda into the cup that forms the crater.
When you are ready, quickly pour the red liquid mixture into the cup with the baking soda. The eruption will start right away. Watch what happens as the volcano erupts. The baking soda and vinegar have a chemical reaction and produce carbon dioxide gas, which makes the dish soap foam and bubble.