Ice Art

    Kids, make a colorful ice sculpture while learning about freezing point depression.  All you need is ice, salt, and food coloring!  You can use any type of salt. Coarse versions like rock salt or sea salt work great, as does the finer-grained table salt (all of these are sodium chloride, NaCl). You can even use other salt compositions like Epsom salts (magnesium sulfate, MgSO4).  For colors use water-based paints such as watercolors or tempera paints, or food coloring.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    What To Do

    1. Make ice. You can use ice cubes but larger pieces of ice are better. Freeze water in shallow plastic, disposable storage containers. Fill them only part way to make relatively thin pieces of ice. This is because the salt can melt holes all the way through thin pieces, making interesting ice tunnels.
    2. When you’re ready, remove the blocks of ice and place them on a cookie sheet or in a shallow pan. If the ice doesn't come out easily, run warm water around the bottom of the container.
    3. Sprinkle salt onto the ice or make little salt piles on top of the ice. Experiment!
    4. Dot the surface with coloring. The coloring doesn't color the frozen ice, but it follows the melting pattern. You'll be able to see channels, holes, and tunnels in the ice, plus it looks like art work. 
    5. You can add more salt and coloring, or not. Explore however you like.
    6. NOTE!  This is a messy project. You should perform it outdoors or in a kitchen or bathroom. The coloring will stain hands and clothes and surfaces.

    How It Works

    The salt lowers the freezing point of water through a process called freezing point depression. The ice starts to melt because it is above its freezing point. It makes liquid water. Salt dissolves in the water, adding ions that increase the temperature at which the water could re-freeze. As the ice melts, energy is drawn from the water, making it colder. Salt is used in ice cream makers for this reason. It makes the ice cream cold enough to freeze. Did you notice how the water feels colder than the ice cube? The ice exposed to the salty water melts faster than other ice, so holes and channels form.

    from Anne Marie Helmenstine