Schematic of the experimental procedure for tests on real paint samples. Paint fragments were taken from ‘Leaves in the Brook’, a painting by J. E. H. MacDonald (1873–1931) (made circa 1918, oil on board, 21.3 x 26.6 cm, McMichael Canadian Art Collection, Kleinburg, gift of the Founders, Robert and Signe McMichael, 1966.16.35). Credit: HIMS Even small amounts of water can lead to rapid formation of metal soap crystals in historical oil paintings. Researchers at the University of Amst...