Grow A Giant Crystal

A crystal is a solid material made up of molecules that fit together in a repeating pattern. These patterns form the materials into very interesting shapes.

The process of crystal formation is called crystallization.  Many crystals form as liquids cool and solidify, such as snowflakes that form when water freezes and certain gemstones that form when magma hardens.  Some crystals are formed when water evaporates from a mixture, such as salt crystals that form when sea water dries.  Alum crystals are also formed as a result of evaporation.

In this project, you will be forming a crystal from a solution of water and alum.  Alum, or aluminum potassium, is a chemical usually sold in powder form in the canning or spice aisle of the grocery store.  It's most common use is in making crisp pickles and maraschino cherries.

This is a great science project for kids and adults alike (especially for rock enthusiasts)!  How big will your crystal grow?

Notes
Young children will require assistance.  This project uses very hot water that can scald and alum, a kitchen chemical that is considered safe, but still should not be consumed.

Time Needed

7 Days (less for a smaller crystal, more for a larger one)

Supplies Needed

• 2 Heat-safe Jars (16oz size works well)
• Water
• Alum (no set amount - you will need more to grow a larger crystal.  Start with 8oz)
• Thread
• Popsicle Stick or Pencil/Small Dowel

Instructions

1. Pour a 1/2 cup of water into a jar.  Heat the water in the microwave until it is almost boiling.
2. Add 2 1/2 tbsp of the alum to the water.  Stir until the alum is dissolved (this may take several minutes).
3. Place the jar in the freezer for 10 minutes.
4. Transfer the jar to the refrigerator.  Make sure you put it in a place where the temperature will stay constant and the jar will not be disturbed.
5. You may see tiny crystals at the bottom of the jar within three hours, but it is best to give the seed crystals at least a full day to grow.  Crystals require patience!
6. Strain the seed crystals out of the water.  Select the very best crystal (largest size, best shape) and set it aside.
7. Repeat Steps 1-2.  Decant the mixture into a clean jar (leaving any sediment in the bottom of the first jar).
8. Place the jar with the alum-water in the freezer for 10 minutes.
9. Meanwhile, tie one end of the thread securely to the center of the popsicle stick.  The thread needs to be long enough to suspend the seed crystal in the middle of the water.  
10. Start a knot in the other end of your thread, but don't tighten it (leave a loop that can be tightened around the seed crystal).  Set the crystal on a flat surface.  Place the knot loop over the crystal and tighten it.  This might take a couple of tries!  Cut off any excess thread.
11. When the alum-water is out of the freezer, place the stick with the attached crystal over the jar so that the crystal is suspended directly in the middle of the jar and liquid.  
12. Place the jar in the refrigerator.  Growth will begin within three hours, but it is best to leave the crystal in the solution for a couple of days.
13. Remove the crystal from the water and hang it somewhere safe.
14. Repeat Steps 7-8.
15. When the alum-water is out of the freezer, replace the stick with the attached crystal.  Place the jar in the refrigerator.  Growth will begin within three hours, but it is best to leave the crystal in the solution for a couple of days.
16. Repeat Steps 14-15 as many times as you would like.  You may have to wind up the string as the crystal grows to keep it off of the bottom of the jar.
17. Amaze and delight your friends and family with your beautiful, giant alum crystal!