The lab comes in a kit we purchase from WARD'S Natural Science, which includes this 2-part activity plus another activity related to ocean currents. The kit is called "Exploring Convection." To make the blue ice cubes, add 3 drops of food coloring to each empty cube mold in an ice cube tray, add water, and freeze.
CLICK HERE to see a video of "Part I".
CLICK HERE to see a video of the other lab included in the kit (related to ocean currents).