Replicas of two terracotta warriors painted in what experts believe were the original colours. After investigating traces of paint on the statues, conservation experts think no two were painted the same.
Credit: British Museum/C Roth
HOW DO YOU MAKE PURPLE? Any kid fresh out of art class will tell you: just mix blue and red.
Sounds simple, but new research reveals a story about purple that spans almost three millennia and involves a buried army, immortality, Einstein, a lost dimension, and your favourite pair of faded blue jeans. It begins, prosaically enough, with the search for water.
In the spring of 1974, Shaanxi province in central China was suffering a drought. Near the city of Lintong, local farmers began digging an irrigation well. They didn't find water – but what they did find is now widely regarded as the eighth wonder of the world: the Terracotta Army.
The farmers had stumbled upon part of the burial complex of Qin Shi Huang, the First Emperor of China, who died in 210 BC. According to the beliefs of the era, to accompany and protect him in the afterlife, he required a spirit army. More than 8,000 life-sized terracotta warriors, horses and other figures were made just for this purpose.
Today the warriors are a natural terracotta colour, but they weren't always so. Catharina Blänsdorf is an expert on conservation at the Technical University in Munich, Germany. She is currently in Lintong investigating what the terracotta warriors would have looked like more than 2,000 years ago, using minute traces of paint that remain on their surface.
She explains that the lacquer that binds the pigments to the terracotta was waterlogged, and dried out after excavation, causing the flaking and loss of paint that survived the lengthy burial. So what did the warriors look like originally?
"Extremely colourful and each different," she says. "I did not find two with the same colours." Blänsdorf doubts the real-life Qin army was ever so colourful, however, "as the peasant soldiers could have hardly afforded these kinds of clothes".
ONE OF THE COLOURS worn by the model warriors – especially those representing the highest-ranking officers – was purple. This presented an interesting conundrum to archaeologists, because purple pigments are rarely found on ancient artefacts.
"Blue, and purple too, are not earth colours. You don't find them in surface soils," says Heinz Berke, a chemist and expert on ancient pigments at the University of Zurich in Switzerland.
Blue pigments only began to appear in human history when mining began, and even then they remained rare – as was the case with lapis lazuli, a blue-coloured stone. "For the whole ancient world there was only one mine, found in today's Afghanistan," says Berke. "It was very rare blue stuff, and very expensive." For the Egyptians, it rivalled gold in status, so they were often used together, he adds.
There were no easy substitutes, because most other mineral pigments and plant dyes don't maintain their colour. "They are not stable enough," explains Berke, citing the way indigo dye fades from blue jeans. He adds that dyes can't be used as pigments anyway.
Dye molecules adhere well to fibres, but not to hard surfaces such as terracotta. With pigments, on the other hand, the molecules form into tiny grains, and when mixed with a binder such as egg yolk, oil, or lacquer, they can be painted onto solid surfaces.
Dyes were still valuable though. From ancient Lebanon through Roman times, a purple dye extracted from molluscs was so rare and precious it became a status symbol. To this day, purple remains associated with royalty, power and wealth.
In the early 1990s, detailed chemical analysis by researchers at the Bavarian State Department of Historical Monument in Munich, Germany, revealed that the purple found on the terracotta warriors is a barium copper silicate with the chemical formula BaCuSi2O6. It has also been found on artefacts from the Han dynasty (206 BC to 220 AD), and was dubbed 'Han purple' – though it has since been detected on artefacts dating back to 700 BC or earlier.
