Just like its store-bought cousins, this mesmerizing homemade lava lamp relies on a simple scientific fact: oil and water don't mix. When you pour both into a bottle, the denser water sinks to the bottom, leaving the oil on top. A store-bought lamp uses heat to propel the water up through the oil, but here the fizz from an antacid tablet triggers the frenetic action. The carbon dioxide bubbles shoot globules of colored water upward, and the globules drift back to the bottom as the bubbles disperse.
Fill the bottle just over halfway with the oil, then add water, to an inch from the top. Add 10 drops of food coloring.
Place the bottle on the pie pan to catch potential spills. Cut or break an antacid tablet in quarters and drop one quarter into the bottle. When the bubbling slows, add another quarter-tablet to get it started again. (Adding too many tablets at once will cloud the oil with bubbles.)
To store the lamp, let the bottle sit until all the bubbles have completely dispersed. This prevents the buildup of gas in the bottle. Cap it and put it in a safe place to prevent spills.