Water can be substituted for the alcohol. If you use metallic paint Please Use Glass Bottles . The thinner and paint might react with or soften the plastic. Fill the bottle half full with water or alcohol. Add a few drops of food coloring and a few drops of silver or gold paint.
Metallic paints contain small flecks of metal which enhance the effect of the wave motion.
Pour any of the oils into the bottle until it is full. Attach lid to the bottle. Shake the bottle. The water, alcohol, and oils mix but soon separate. The color will be on top.