The volcano can be as large or as small as you'd like it to be, and you could also just cover up a sixteen or twenty ounce bottle.
(1) Use a sheet of plywood roughly eight inches longer and wider than the base of your volcano. This will prevent the lava from your volcano from making too much of a mess. Alternatively, you could try and put it down on a sheet, but keep in mind that the food coloring will leave a stain.
(2) Now use your clay or papier mache to build your volcano mountain around the empty bottle. Don't put the lid on it, otherwise you won't be able to make your lava. Make sure the mouth of your volcano is tight against the mouth of the bottle, or your lava will just drip into it. Have fun making creases for the lava to flow down! You can also get some little plastic trees or plants to decorate with.
(3) When your mountain is dry, paint it with your paints and brushes.
(4) Now mix 1 teaspoon of liquid dish soap, 1 teaspoon of baking soda, and a few drops of your food coloring in a cup or a small bowl. If you are carrying the project to school or another place, leave this step until just before you are giving the presentation.
(5) Using a funnel, pour this mixture into the mouth of a bottle.
(6) Now set your volcano on a nice flat surface.
(7) Using your funnel again, pour about a fourth of a cup of white vinegar into the bottle. Your volcano will now erupt!
Step back to make sure you don't get any of the lava mixture on your hands and clothes. If you're careful, you can use this volcano a few more times. It's recommended to use some kind of sealant if you want to preserve it for any length of time.
If you don't want to build a volcano, but would still like to see an eruption, it's easy to take the bottle, baking soda, and vinegar outside and watch it over and over again.