 Pigments bound in glue had an optical quality that rendered them opaque in appearance and unusually vivid. Unlike oil, which makes chalk appear translucent, chalk mixed in glue is rendered as stark white. Similarly, more expensive pigments assume brilliant opacity in a glue medium. The whites are chalk in areas mixed with lead white, especially in the Magdalen's mantle and veil, Christ's shroud and the Virgin's veil. The artist used four blue pigments, an unusual number for paintings of the period, with indigo predominating. As a plant-derived pigment, indigo it has a tendency to fade over time. Azurite and lead-white line the under-paint, while the landscape contains indigo mixed with lead-tin yellow. The sky and Nicodemus' collar are painted with lighter and less intense azurite, while the Virgin's dress is azurite mixed with ultramarine and smalt, a blue ground-glass pigment. The Entombment is one of the earliest Western pictorial works of art in which the use of smalt could be ascertained and its presence proves that the pigment was not invented during the sixteenth century, as had previously been believed.
