This beautiful diptych painted by Hans Memling shows how the Early Netherlandish painters were masters at conveying textural expression and realism. However, one detail that immediately catches the eye is Maarten van Nieuwenhove’s velvet tunic. It does not look quite as Memling probably intended; what has happened to the layers of paint here? Paint consists of several different elements, including pigments. Pigments are dyes that give paint its colour and can be made from various materials: earth (ochres, umbers), stones (lapis lazuli, azurite), animals (cochineal, sometimes even Egyptian mummies!) and plants (madder). Pigments could also be created by chemical processes (lead white, Verdigris). Artists had to know a lot about the properties of these pigments and how to make paint from them. What they could not always foresee, however, was the durability of certain pigments, particularly organic ones. Indeed, over the centuries, some paint layers changed colour or even disappeared. As is the case with the Diptych of Maarten van Nieuwenhove, this can sometimes really change the appearance of the painting!