Considered the pinnacle of mediaeval painting, the Ghent Altarpiece was painted around 1432 by Jan van Eyck and probably his brother Hubert. It is currently undergoing the most extensive conservation treatment for more than a century. The decision to remove all overpaint was underpinned by scientific arguments: Belgian researchers report in the journal Angewandte Chemie about their use of “chemical maps” to visualize the original paint layers under the overpainted surface.