Harry laughed at that. "Alright, let's start this lesson, shall we? Right ... Foundation Alchemy, Class One. There are three stages to the alchemical process, called the Nigredo, the Albedo and the Rubedo. Physical alchemy is what most alchemists seek to achieve, that's the Opus Alchymicum that almost all of them embark upon. To be considered to have completed the Opus, the full alchemical Work, an alchemist must be able to produce not only gold and the Elixir of Life, but an actual Philosopher's Stone."