Many children and students grow sugar or salt crystals at some point in their education. While these crystals are fun and easy to grow--and edible if you use sugar and flavour extracts--you can only vary them so much. The crystals usually turn out small and the colours muddled. Older students and adults can grow large, beautiful, bright blue crystals with copper sulphate. You can either grow them free-form in the bottom of a container or create homemade geodes with eggshells.
Mix 1 cup of distilled water with ½ cup of copper sulphate granules in a small saucepan. Stir them gently over low heat until most of the copper sulphate granules dissolve. The result should be a cloudy blue liquid.
Remove the saucepan from heat and hold a glass jar over the hot burner until the glass feels warm to the touch. This prevents the jar from cracking because of a sudden temperature change.
Pour the cloudy blue mixture into the warmed jar and set it in a warm, dry place overnight. Over the next few days you should see brilliant blue crystals about the size of the tip of your finger beginning to form. For clusters, allow the jar to sit until most of the liquid is gone.
For natural-looking clusters, place a rough, porous stone in the bottom of the jar. The crystals will grow on its surface. Make an egg geode by cracking an egg in half with minimal damage to the shell. Clean the egg from the shell and spoon a little of the mixture into each half. Place the shells in a bowl of sand or salt to keep them upright.
Do not use the tools you used to make the crystals to make food, and do not eat or lick the crystals; they can be toxic. Wash your hands and work area thoroughly after making your crystals.