Q sniffs appreciatively. The smell of old books is one of his favourites. He beams and flushes, very pleased that Severus likes the book.
"Well," he says, brow wrinkling in thought. "I thought it might refer to the colour spectrum since it goes from black to white. Perhaps having to do with how things would change colours as you mixed the ingredients. And," he goes on. "Don't you change the colour of black quartz to citrine by heating?" Q looks at Severus. "I'm not sure about the rest of the verse. Is it referring to more stones? Or metal? The green being copper and of course, lead."