Things You'll Need
Instructions
Mix alum and water in the pot. Heat over medium heat while stirring constantly until the alum is completely dissolved.
Pour the mixture into the jar and allow it to set for at least 24 hours. This will allow the mixture to cure quickly, and by the next day the bottom of the jar will be filled with many small crystals.
To make larger crystals, after pouring the liquid into the jar, place it in the ice chest so that it will cool more slowly. Wait the 24 hours, then open the ice chest. You should have 3 to 5 larger crystals. You can also set the jar in a bowl of hot water inside the ice chest to slow the cooling even further.