Rainbow Milk Science: Video

Milk, food coloring and liquid soap are all you need for this beautiful activity that doubles as a lesson in surface tension. Milk (and all liquids) contain a property known as surface tension. Surface tension is caused by the cohesive forces of the liquid’s molecules. Soap, when applied to any liquid, will reduce the surface tension. If this is the case, what will happen when we add liquid soap to the milk with food coloring droplets?


  • a shallow container (a shallow bowl or tray will work)
  • milk (we used about 1 cup)
  • liquid dish soap
  • a small container for the dish soap
  • q-tips
  • liquid food coloring



      1. Pour 1 cup of milk into a pie-sized shallow container.



      1. Squeeze several drops of different colors of food coloring into the milk.



      1. Squeeze liquid dish soap into a small container and dip a q-tip into the liquid dish soap.



    1. Dip the q-tip with the liquid dish soap into the milk with food coloring and watch as the colors almost magically move around!

    Alternatively, you can squeeze drops of liquid dish soap into the milk or dump a small container of dish soap right into the milk and watch what happens!