Plastic Fantastic

Salt-powered lava lamp

Item	Amount
Transparent plastic bottle	1 per child
Water
Cooking oil
Food colouring
Salt
Funnel

1. 
   The original lava lamp, invented in the 1960s, worked by using the heat of an electric bulb to melt lumps of coloured wax that then rose through a liquid before cooling and sinking again. You can reuse plastic containers to create similar movement in a salt lava model and encourage children to observe what happens as the materials change.
   

2. 
   Remove any labels from the bottle and fill approximately two thirds of it with water.
   

3. 
   Use a funnel to add a couple of drops of food colouring and about 50mls of oil. Lighter coloured food colouring will make the globules easier to see.
   

4. 
   Allow the contents to settle: the food colouring will colour the water, while the oil forms a layer on the surface.
   

5. 
   To make the ‘lava lamp’ work, gradually add half teaspoons of salt into the bottle. The more salt you add, the more globules you’ll see. The additional weight on the surface will initially force globules of oil to sink. As the salt dissolves in the water, the oil will rise back to the surface.
   

6. 
   You can add salt until the water becomes saturated. A transparent plastic container/beaker will increase the surface area on which to add the salt, but a bottle and lid might ensure fewer spills!