To craft an item or potion in The Witcher 2: Assassins of Kings, you will need to find the crafting diagram and take it to a Craftsman.

Alchemy plays a big part in The Witcher 3, and we are here to help you out with the potion and decoction-making aspect ... This diagram is in the underwater cave that takes you to “Lornuk ...

A diagram from The Witch Queen Collector's Edition shows elements and alchemy symbols under Light classes . Alchemy was studied across multiple centuries, countries, and religious beliefs.