There are four basic elements in the universe: Water, Earth, Air and Fire. It's said that if you mix these four elements together in different proportions under some kind of mysterious force, you will get different substances. There are five rewards to choose from: Crops/Timber/Stone/Iron/gold. Every day after 0000 you can choose one or more rewards for free. You can also pay 4 Diamonds to receive an additional reward (2 during Ultimate Alchemy Paradise event). After you have received 15 rewards you can open a chest that contains one piece or armor or weapon based on your hierarchy.