Blue

Blue is the colour of the sky and the deep sea, and its symbolism is dominated by distance, depth, calm and the transcendent. A striking historical fact underlies its prestige: a true, stable blue pigment was hard and costly to make, and ultramarine, ground from lapis lazuli imported from Afghanistan, was for centuries more expensive than gold, which is why medieval and Renaissance painters reserved it for the robe of the Virgin Mary, whose blue mantle became one of the most recognisable colour codes in Western art.

In many cultures blue is protective: the blue eye-bead against the evil eye runs from the eastern Mediterranean across the Islamic world. In Hindu iconography a blue skin marks Vishnu, Krishna and Rama, the divine associated with the infinite of sky and ocean. Blue is now the most commonly named favourite colour worldwide, a modern preference. In the twentieth-century chakra scheme blue is placed at the throat.

Blue is rare as a stable pigment in nature, and the history of the colour is largely the history of the expense of obtaining it.

Ultramarine was ground from lapis lazuli, and until the nineteenth century essentially all of it came from the mines of Badakhshan in what is now Afghanistan. It reached European workshops after a journey of thousands of miles and was priced by weight against gold, which is why medieval and Renaissance contracts specify how much ultramarine a painter is to use and reserve it for the Virgin's mantle. The alternative mineral blue, azurite, was cheaper, commoner and greener, and it degrades toward green over time.

Egypt solved the problem earlier than anyone. Egyptian blue, a calcium copper silicate made by firing sand, lime and a copper compound together, is the earliest known synthetic pigment, in use from the third millennium BCE, and its manufacture was subsequently lost. In Mesoamerica, Maya blue was made by binding indigo dye into palygorskite clay, producing a blue of extraordinary durability that survives on murals exposed to tropical weather for a millennium.

For cloth the sources were woad in Europe and indigo from India and elsewhere, chemically the same dye from different plants and the subject of long commercial conflict.

Synthetic ultramarine, produced from the 1820s, collapsed the price of the most expensive colour in the palette within a generation. Every claim about blue as the colour of the sacred and the royal was formed before that happened.