Experiment 2: Growing Large Crystals with Seed Crystals

What you need.

  • Chemicals for crystal growing. We have suggestions in our chemical chart.
  • Forceps (tweezers).
  • Eye protection.
  • Disposable gloves for handling crystals.
  • Filter funnels.
  • Filter paper.
  • Jars with lids.
  • Small glass or 50ml beaker.
  • Cotton thread.
  • Stirring rods.
  • Pot for heating water.
  • Heat source.
  • Pot holder.
  • Thermometer.
  • Distilled water.

What to do.

Prepare a saturated solution of one of your chemicals. Pour 100ml of distilled water into a clean jar. Place the jar into a pot that is half full of water. Heat this double-boiler arrangement on a stove or hot plate and begin adding dry chemical to the water in the jar. Heat the water in the jar to 50°C (122°F). Add chemical and stir until no more dissolves in the liquid. Use a pot holder to remove the jar from the double boiler. Cover the jar and allow the liquid inside to cool to room temperature. Add a few more grains of chemical, secure the lid, and shake the jar. Shake the jar twice a day for the next two days. The added grains will not dissolve (they may even grow slightly). This procedure will create an ideal medium for growing crystals later in this experiment.

After two days, gently pour about an ounce (30ml) of the solution into a small glass or 50ml beaker. Set aside undisturbed for another day. Check for tiny seed crystals forming on the bottom. When you find one that has reached the size of a rice grain, pluck it out with forceps, and place it on a paper towel to dry. Harvest as many well-formed individual seed crystals as possible before discarding the contents of the 50ml beaker.

Now, return to the jar containing the prepared solution. To supersaturate this solution, place the jar in the double-boiler again and heat to 50°C until the remaining grains of chemical disappear. Then, add a small amount of additional dry chemical and stir the solution. Remove the jar from the heat, cover, and allow to cool.

Cut a piece of thread that is one inch shorter than the height of the jar. Tie a seed crystal to one end of the thread. Using a nail and hammer, punch three holes through the lid forming a small triangle near the center. Loop the thread through the holes so the free end sticks out and allows you to adjust the string length inside the jar.

Screw the lid back on the jar with the seed crystal suspended in the solution. In a few hours, a larger crystal will begin forming around the seed crystal. After a few days, you will have a good-sized specimen. Adjust the thread length so the growing crystal does not touch the inside of the jar.

When you feel the crystal has grown enough, remove it from the jar and carefully dry it with a paper towel. Wrap the finished crystal crystal in a soft cloth or paper towel for protection.

What can be learned.

Crystals grow in a supersaturated solution by the orderly addition of material onto the faces of a "seed" crystal. Distinct crystal shapes can be grown using different chemical solutions. Large, well-formed crystals can be used to study the different crystal classes.