Johannes Vermeer's luminous paintings are loved and admired around the world, yet we do not understand how they were made. We see sunlit spaces; the glimmer of satin, silver, and linen; we see the softness of a hand on a lute string or letter. We recognise the distilled impression of a moment of time; and we feel it to be real. We might hope for some answers from the experts, but they are confounded too. Even with the modern technology available, they do not know why there is no evidence of any preliminary drawing; why there are shifts in focus; and why his pictures are unusually blurred. Some wonder if he might possibly have used a camera obscura to capture what he saw before him. The few traces Vermeer has left behind tell us little: there are no letters or diaries; and no reports of him at work. Jane Jelley has taken a new path in this detective story. A painter herself, she has worked with the materials of his time: the cochineal insect and lapis lazuli; the sheep bones, soot, earth, and rust. She shows us how painters made their pictures layer by layer; she investigates old secrets; and hears travellers' tales. She explores how Vermeer could have used a lens in the creation of his masterpieces. The clues were there all along. After all this time, now we can unlock the studio door, and catch a glimpse of Vermeer inside, painting light.