Science Fun

Cool Crystals


  • ¼ cup Epsom salt
  • ¼ cup hot water
  • Food coloring
  • A cup
  • A plate
  • Optional: a small jar


  1. In the cup, measure out ¼ cup Epsom salt and ¼ hot water from the sink. Stir them together.
  2. If all the salt doesn’t dissolve, heat the cut in the microwave for 20-30 seconds.
  3. When all the salt is dissolved, put a drop or two of food coloring in the cup and stir to mix.
  4. Place the cup in the refrigerator. Check on it every half hour or hour. Within 4 hours, crystals should form in the bottom of the cup.
  5. Scoop the crystals onto a plate using a fork.
  6. If you want the crystals to last longer, put them in a jar with a lid (the small jars that baby food comes in work well).

How does it work?

More salt can dissolve in hot water than cold, so when the hot water cools in the microwave, the Epsom salts create crystals on the side of the cup. The unique shape of Epsom salt molecules makes them form long crystals that almost look like needles. Different crystals have different shapes. If you look at sugar or salt crystals under a magnifying glass, you can see their cool crystal shapes, too!

Further Exploration:

  • When crystals form after being dissolved, they will cling onto anything they can. You can drop a bottle cap into your cup of dissolved salt and they will form on it. You can make a sculpture out of pipe cleaners and they will form on that, too.
  • Does the experiment work with room temperature water? Cold water?
Video of experiment here!