STEM at Home is a series by BrainSTEM to encourage families to do fun experiments and learn from the world around them. This week, we’re learning how to make epsom salt crystals. Crystals are so common because the word crystal refers to any matter that is arranged in an ordered form. The units that are arranged can be molecules, atoms or ions which are all much too small to see with the naked eye.

Key Concepts

  • molecular structure
  • atoms
  • supersaturate 
  • evaporate


  • a pencil or butter knife
  • cotton string (do not use nylon string)
  • scissors to cut the string
  • something to weight down the string so it won’t float (we used an old washer tool)
  • water (tap water)
  • Epsom salt 
  • glass or mason jar
  • saucepan for boiling water
  • measuring cup or any small cup
  • food coloring (optional)
epsom salt crystals

epsom salt crystals


  1. You will be using a ratio of 1:1 water to Epsom Salt (1 cup of water and 1 cup of Epsom Salt for example) for this project and put them in your saucepan. Stir the salt and water for 1-2 minutes to dissolve the salt
  2. Heat the salt mixture until very warm then let it cool down.
  3. Tie your cotton string to the pencil (or butter knife) You will want it to hang the weight just slightly above the bottom of the glass. 
  4. Pour the cooled the mixture into your glass(about 1 cm. form the glass mouth).
  5. Add any food coloring. (Optional.)
  6. Put the weighted string into the mixture.
  7. Put in the refrigerator and let it sit overnight.
  8. Come back to check them tomorrow.

Questions you may ask

  1. What did you see on the string?
  2. What’s happened if you put food coloring in the mixture?
  3. When you use the magnify glass to look at the crystal what does it look like?
  4. Can you try making Epsom Salt crystal from a pipe cleaner in a heart shape?
  5. Can you use others salt or sugar?

Scientific Facts

Epsom salt is another name for magnesium sulfate. The temperature of the water determines how much magnesium sulfate it can hold; magnesium sulfate will dissolve more when it is hotter.

Cooling the solution rapidly encourages fast crystal growth since there is less room for the dissolved salt in the cooler, denser solution. As the solution cools, the magnesium sulfate atoms run into each other and join together in a crystal structure.