Crystals form when molecules in a liquid solution meet and bond together in a repeating, orderly pattern. To trigger this, you must heat water to increase its solubility, dissolve a crystal-growing medium (like salt or alum), and then let it cool. As the water cools or evaporates, it can no longer hold the dissolved particles, causing them to "crash out" of the liquid and latch onto a surface. Essential Tools and Safety Before beginning, gather your basic supplies: Heat-resistant glass jars (mason jars work best).