Cobalt blue
Cobalt blue in impure forms had long been used in Chinese porcelain, but it was independently discovered as a pure alumina-based pigment by Louis Jacques Thénard in 1802. Commercial production began in France in 1807. The first recorded use of "cobalt blue" as a color name in English was in 1777. The leading world manufacturer of cobalt blue in the 19th century was Benjamin Wegner's Norwegian company Blaafarveværket ("blue colour works" in Dano-Norwegian). Germany was also famous for production, especially the blue colour works ("Blaufarbenwerke") in the Ore Mountains of Saxony.
The Entombment (Bouts)
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.
The greens are mostly verdigris, although those predominant in the landscape are mostly blends of blue and yellow pigments, and the green of the cloth worn by Mary Salome is malachite mixed with yellow lake. The browns are blends of reds and blacks. John's red robe is composed from cinnabar and vermilion made from rubia and insect dyes. Some of the reds are mixed with earth colours not susceptible to the effects of light, and have thus survived close to their original appearance. The black pigments are generally bone blacks but in places from charcoal. The blacks are mixed with chalk in areas, producing a red to brownish 'earthy' appearance.