These crystals are easy to grow, only take a few hours, and don't require boiling water or harmful chemicals. Perfect, right? All you need is a cup, Epsom salts, and hot tap water. In the cup, stir together equal amounts of Epsom salts and hot tap water (you can microwave the water for 45 seconds to a minute if you prefer, but don't boil it). If you want colored crystals, add a few drops of food coloring. Set the cup in the refrigerator to cool, undisturbed, for at least a couple of hours. Drain off the water and this is what you'll have. If you like, you can slide the crystals out of the cup and set them on a paper towel to dry and keep.