In the medieval period, artists had roughly five sources of the color: ultramarine, azurite, Egyptian blue, smalt, and vivianite. The most prized of these was ultramarine, more commonly known in its ground and purified form as lapis lazuli. Found only in one region of Afghanistan, for millennia lapis lazuli demanded the same price as gold. It wasn’t, in other words, something you’d expect to find in random medieval dental calculus. “This isn’t a kind of paint you just give to someone who’s learning,” Beach says (contrary to the suggestion of an outside reader evaluating the paper before publication, who believed the woman was just a janitor cleaning up after the real manuscript makers).