The Italian artist has long been suspected of turning his studio into a giant camera obscura, punching a hole in the ceiling to help project images on to his canvas. But new research claims that Caravaggio also used chemicals to turn his canvases into primitive photographic film, “burning” images he then sketched on to for works such as St Matthew and the Angel. “We were already sure Caravaggio projected images of his sitters, but we have now found mercury salt in his canvases, which is light-sensitive and used in film,” said Roberta Lapucci, conservation chief at Florence’s SACI institute.