In the 17th century, painters, including Rembrandt, made their own paints by mixing pigments with an oil binding medium. They bought their materials at an apothecary’s shop and from colour merchants. Although the choice of pigments was limited, Rembrandt knew exactly how to combine them to manipulate colour contrast, texture and translucency.
Blue glass
Smalt is the most important blue pigment on Rembrandt’s palette and is used extensively in The Night Watch. It consists of a finely ground blue glass and was made by melting quartz, in the form of sand, together with potash, potassium salts added to make the pigment flow more easily, and zaffer, cobalt ore roasted with a little sand, which gives smalt its intense blue colour (Fig. 1). The mixture was heated at around 1200°C for at least 5 hours, often longer, in a glass makers kiln.
In the seventeenth century, the cobalt ore came from the Erzgebirge, in the German region Saxony, to the Netherlands. Here, in around 1600, important glass works were established in Middelburg and Amsterdam by glass makers from Antwerp and Italy, who brought specialist knowledge on how to make coloured glass. The blue glass was ground using wind power in several windmills. Dutch smalt was praised for its high quality, and you would even find it in seventeenth-century Italian price lists for pigments.
Kleurverlies
Rembrandt applied it not only for its blue colour, but also mixed with red or yellow pigments to make purple or green, and used it to enliven brown tones. It also could give more texture to his paints and made them dry faster. Unfortunately, smalt mixed with an oil binding medium tends to lose its colour, changing areas of bright blue into a murky brown.
Rembrandt used smalt in the background architecture, added to brown earth pigments, and brushed on with broad textured strokes (Fig. 2). He also applied it in the shadows of the blue details in the costume of Van Ruytenburch (Fig. 3). However, in The Night Watch, there is little intact blue smalt left.
