One of the Terracotta Soldiers from the tomb of Qin Shi Huang (ca. 200 BC)

In the spring of 1974 a group of farmers digging a well in Shaanxi China about one and a half kilometers (1 mile) north of Mount Li stumbled into an amazing find. A life-sized army of terracotta soldiers numbering over 8000 was entombed in the immense necropolis of Qin Shi Huang, the first emperor of China who lived from 259 BC – 210 BC.  However the story of the despotic Qin Shi Huang (one of history’s most remarkable figures) and his extravagant mausoleum will have to wait.  This post is not about the cruel emperor or his terracotta army, but is rather about the colors found on the terracotta figures, which were originally lacquered with a rainbow of bright colors– pink, red, green, blue, black, brown, white, and lilac.  One of the pigments discovered by archaeologists was Han purple, a manufactured pigment which was in use in China from about 1200 BC to 220 AD.  The secret to making Han purple was lost in antiquity and could not be rediscovered until modern spectroscopy helped chemists rediscover the materials used.

A Modern Reproduction of how the figures originally looked--although no two were painted the same (Credit: British Museum/C Roth)

Many scholars believe that Han purple was accidentally discovered by Taoist alchemists seeking to create synthetic jade.  The compound was a barium copper silicate which was fired for long periods of time at temperatures around 900-1000 °C.  The compound was probably produced in kilns north of the city of Xian (which was once known as Chang’an and was the capital city of China during the Zhou, Qin, Han, Sui, and Tang dynasties).

Modern Han Purple Pigment

Han Blue was a dark bluish purple/indigo.  It became more purplish over time as the barium copper silicate deteriorated and red copper oxides were formed.  The pigment was used for beads, ceramic vessels, paintings, and for octagonal pigment sticks (which may have had a ceremonial value in their own right).

Han purple had a very similar companion compound–Han blue—which was also a barium copper silicate.  Because of certain quirks of chemistry, Han blue was more lightfast than than Han purple and had fungicidal properties to boot.  This allowed Han blue to last for the long centuries, whereas Han purple is now known mostly from faded traces. Han purple was not fungicidal and compounds (namely oxalates) produced by certain long-lived lichen caused the pigment to turn into light blue powder.