Egyptian blue, the first human-made colour, vanished for centuries
More than five thousand years ago, Egyptian craftsmen heated quartz sand, lime and a copper mineral such as malachite together and created a brilliant blue that nature never supplied in easy form. Egyptian blue became the favourite blue of Roman antiquity, then faded from use during the Middle Ages until excavations at Pompeii and Herculaneum brought it back to light.
A pigment is a coloured substance that stays as solid particles rather than dissolving, which is what separates it from a dye. It looks coloured because it soaks up some wavelengths of light and bounces back the rest, and the way its atoms bond decides which ones. That is also why pigments can look different under a lamp than outdoors: sunlight has a fairly even spread of colours, so colour scientists use a daylight standard, D65, set at about 6500 kelvin.
Humans have been at this a very long time. Pigments and grinding tools reported from a cave at Twin Rivers near Lusaka in Zambia may be 350,000 to 400,000 years old. Ochre, an iron oxide, was the first paint colour, and charcoal supplied black. Many earth pigments still carry the names of the places they were dug from: sienna from Siena and umber from Umbria. Chemists later learned to make these colours more consistently, but the old names stayed.
Blue was always the hardest. Egyptian blue appears on an alabaster bowl from around 3250 BC. The precious alternative was lapis lazuli, so costly that substitutes were constantly sought. Prussian blue, the oldest modern synthetic pigment, turned up by accident in 1704, and by the early nineteenth century chemists were making a synthetic ultramarine from aluminium silicate and sulfur. The discovery of mauveine in 1856 then opened the door to hundreds of synthetic dyes and pigments and helped organic chemistry flourish.
Colour is now a big business with careful bookkeeping. About 7.4 million tons of pigment were sold worldwide in 2006, and a 2018 estimate put the industry at 30 billion dollars, with titanium dioxide, the brightening white in countless products, worth 13.2 billion a year. The Colour Index International, first published in 1925, assigns each pigment a chemical index number so makers can identify it whatever it is called.
Source: Pigment
