Where is the light coming from in Joseph Wright of Derby’s 1768 painting ‘An Experiment on a Bird in the Air Pump’? It’s a question that art historians have puzzled over for centuries. Because although Wright is known for his luminescent, candlelit paintings, this one doesn’t quite conform: the light is too white, too powerful, and too dispersed to be coming from a single, flickering flame. There’s another way of reading the question: how does a painter manage to create such a radiant canvas from paint alone (go and stand in front of the painting in the National Gallery – you’ll see what I mean). Wright wasn’t the only painter doing this in the 18th century, but nevertheless, the luminosity of the canvas is breathtaking. Even when you get up close, it seems to defy the physics of pigment.

Joseph Wright of Derby’s ‘An Experiment on a Bird in the Air Pump’