A flicker of a half-smile, and he goes to a shelf, takes out a book Albus gave to him during a particularly bad year, and reads, "Then take out all the feces (that is, the end-product of a long preparation beginning in antimony; that's your Green Lion, Quin, or at least the dried remains of its 'blood'), which remain in the retort and are blackish like unto soot, which feces are called our Dragon, of which feces calcine one pound or more at your pleasure in a fervent hot fire in a potter's or glassmaker's furnace, or in a wind furnace until it become a white calx, as white as snow, which white calx keep well, and clean by itself, for it is called the basis and foundation of the Work.*"
He closes the book and puts it back with careful reverence, picks up the other again in the same manner. "At least, I suspect that's the basis of a portion of the selection. Your book-seller was right; even the Hogwarts library didn't have the Compound, although it did have one or two of his lesser works. I hope you didn't have to sell your house for this."