Origin, History and Characteristics
Indigo was probably used as a painting pigment by ancient Greeks and Romans. Marco Polo (thirteenth century) was the first to report on the preparation of indigo in India. The indiagofera tinctoria plant thrives in a tropical climate; the active ingredient is found in the leaves. Aniline blue has the same chemical composition and replaced it in 1870. Indigo does not hold up well in an oil base but makes an excellent watercolor paint.
To prepare the dye, freshly cut plants are soaked until soft, packed into vats and left to ferment. It is then pressed into cakes for use as a watercolor or dried and ground into a fine powder for use as an oil paint. Bound with oil it is very transparent making it a good pigment for glazing. It has a strong yellow undertone. It has fair tinting strength and may fade rapidly when exposed to strong sunlight. Indigo has been used by artists and clothes manufacturing.
Indigo in Vermeer's Painting
Christ in the House of Martha and Mary (detail)
c. 1654 - 1655
Oil on canvas, 160 x 142 cm.
National Gallery of Scotland, Edinburgh
Vermeer is known to have used indigo in only two works. It can be found in an admixture with smalt and in the deep blue robe (see image right) of the seated Christ in Christ in the House of Martha and Mary. This is the only deep blue color in Vermeer's oeuvre where natural ultramarine cannot be found.
The presence of indigo was recently detected with weld in a deep green glaze which covered the dark tone of the background of the Girl with a Pearl Earring. This glaze has almost entirely degraded. It was originally a smooth, glossy, translucent green that imparted depth and, perhaps, the precious quality of enamel to the background.