We used pure vegetable oil, red and blue food colouring, water and Alka-Seltzer tablets. First, we put in a little bit of water into a plastic bottle. Then we filled the rest of it up with vegetable oil, almost to the top. The water and vegetable oil doesn't mix so the vegetable oil sits on top of the water, making two layers.
The next step was to put drops of red/ blue food colouring into the bottle and wait until they all sank to the bottom and rested in the water. Now the fun part! We dropped in half an Alka-Seltzer tablet, put the lid on. It looked like a volcano had erupted. The reason it made an eruption was because a chemical reaction to happened making the red and blue food colouring burst to the top. The gas in the Alka-Seltzer tablets reacts to the water and the gas that is produced wants to escape. The little gas bubbles push up through the water and oil, taking some of the food colouring with it.
We turned the classroom lights off and tried it again. We put a torch underneath the bottle and it lit up like a real lava lamp.
We left it over night to settle and we when we came back into school the vegetable oil was separated from the water again.