Jars are placable, clear items that can be filled with up to 9 bottles of the same potion, so as not to mix potions. It would mainly be used to store potions- you could right click a full potion to empty it into a jar, or right click with an empty bottle to fill a bottle. The Jar filled with potion would reflect the potion's color- for example, an empty jar being filled with a speed potion would be blue, just as a speed potion is, and fill accordingly, just as a cauldron does with varying levels of water. Once filled with a potion, a label would appear, labeling the type of potion within a jar. Not only could this be used as a storage purpose, but for an aesthetic purpose as well. A wizard's tower could have shelves of jars, or a witches hut could contain one. 🙂