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....