Find a large area on a table or counter where you can build your papier-mache volcano. You will need to leave the project there so the papier-mache can dry, the paint can dry and the experiment can be performed. This will take several days. Place the plywood on this surface. Spread newspaper underneath the wood so that some of it sticks out to protect the table top while you are working.
Place the block of wood or the small box in the middle of the plywood. Put the paper cup on top of this block. Bend the chicken wire or screen into a cone shape, making the bottom of the cone wide enough to fit over the block. The top of the cone should be just wide enough for the top of the paper cup to stick out. Use duct tape to connect the cone and form the shape of your volcano's mountain. The screen will support the papier-mache covering, which will make the outside of the mountain. The paper cup will hold the ingredients that form the lava eruption.
Cut the newspaper into long strips of paper that are 2 inches wide. Mix 2 cups of white flour with 6 cups of water in the large plastic bowl to make the paste to attach the papier-mache to the chicken wire framework. Moisten a strip of paper in the flour-and-water paste mixture. Stretch it from the top of the paper cup down the sides of the wire frame to the plywood base. Repeat this until the wire is covered by vertical strips of paper that have been soaked in the paste. Continue building the volcano by adding more layers of papier-mache. You can vary the direction and the thickness in which the strips are placed on the volcano to form the contours of the mountain.
Build the thickness of the papier-mache to about an inch. Then press your hands or a stick into the papier-mache while it is still wet to make cliffs and valleys. Do not cover the top of the volcano; you will need to fill the paper cup after the volcano is ready to produce your eruption of lava.
Let the papier-mache dry thoroughly. This will probably take at least overnight and will depend on the humidity as well as the thickness of your sculpture.
Paint the sides of the volcano so that it looks like a real mountain. Let the paint dry before demonstrating how your papier-mache volcano spouts realistic-looking lava.
Gather your audience. Carefully place 4 tbsp. baking soda into the top of the volcano where you hid the paper cup. Drop in about 6 or 7 drops of red food coloring. When everyone is paying attention, pour 1/2 cup vinegar into the top of the volcano. When the vinegar mixes with the baking soda, a chemical reaction will occur, and the bubbly lava will pour out the top of the volcano and down the sides of the mountain just like lava flows down the slopes of real volcanic mountains.