You make rock candy by dissolving granulated sugar in boiling water until it forms a supersaturated solution, then pouring it into a clean glass jar. Suspend a wooden skewer or string coated in sugar crystals into the liquid so the dissolved sugar can crystallize around it over several days. Place the jar in a warm, quiet location and let it sit undisturbed while large sugar crystals grow on the stick. Once your rock candy crystals reach the desired size, pull them out and let them dry.