Talk:The Witcher 3: Wild Hunt - Guide to Alchemy/@comment-177.67.131.67-20150607142808/@comment-86.63.27.79-20150609191446

In Skellige near a pond north of the Druid Camp you can start a quest called "Practicum in Advanced Alchemy", (There is a grumpy druid sat outside his hut talking to another), completing this should reward you with the formula for Rebis, among others as well. The druid that the quest is for also sells a lot of good ingredients and higher level diagrams once finished.