To get access to the Alchemy Pot, complete the entire story related to the Wight Knight and visit Quester's Rest. Erinn will tell you that she found an interesting thing; the Alchemy Pot. With that, you can create new weapons, armors, accessories, items, etc. Either try your luck or use recipes. You can get recipes from now on by reading books, talking to certain NPCs, or receiving specific sidequests.