Restoring color to China's Terracotta Warriors

Ongoing exhibition shows how researchers are repairing precious relics

XI'AN - Four minutes. Just four minutes is all it takes for the rarest colors on Earth to fade in front of a pair of human eyes. Han blue and Han purple, also called Chinese blue and Chinese purple, are made of synthetic barium copper silicate.

The pigments were first used in paint in the Qin Dynasty (221-206 BC), and in large quantities in the Terracotta Warriors unearthed from the tomb of Emperor Qinshihuang, China's first emperor, who lived between 259-210 BC.