Looking for the perfect blue? You’ll have to specify. Cobalt, Prussian, azurite or ultramarine? According to Philip Ball’s book Bright Earth, if you were an artist living in the 14th century, the finest blue could cost you a king’s ransom. We can’t even reproduce it in this magazine —it’s not part of the gamut, or achievable range of colors, that can be rendered by the four “process colors” of ordinary printing.

The oldest man-made blue —the oldest synthetic pigment, period —is “Egyptian” blue. Color makers fired a mixture of one part lime, one part copper oxide and four parts quartz in a kiln, which left an opaque blue material that can be ground to a fine powder for making paint. The stuff occurs on Egyptian artifacts dating to around 2500 B.C. and was still in use when Mount Vesuvius buried Pompeii in A.D. 79.

In the Middle Ages color became central to the alchemists’ obsession with transmutation. And the alchemists’ great contribution to artists’ blue was ultramarine. It is made from blue lapis lazuli, a semiprecious stone then mined in Afghanistan. The costly raw material and elaborate preparation —which involved endless kneading of the lapis powder and washing in lye —led to the deep, rich, dark blue seen, as Ball points out, in paintings of the robe of the Virgin Mary. The medieval painter’s patron who could afford a Virgin in ultramarine was displaying the piety of an archbishop and the wealth of a modern hedge-fund manager.

As late as 1800, despite several alternative blues, artists were still seeking a less costly substitute to ultramarine. In 1824 the French Society for the Encouragement of National Industry offered 6,000 francs for an industrial process that could make a synthetic ultramarine for less than 300 francs a kilogram. A color manufacturer named Jean-Baptiste Guimet claimed the prize, and by the 1870s the snob appeal of the natural pigment had died out —killed by time and a price between 100 and 2,500 times higher than the synthetic variety. Industrial ultramarine became the blue of choice in the work of Impressionists such as Renoir, Czanne and van Gogh.