Detail of a mural from an Eastern Han tomb with artificial pigment

Han Purple: A 2,800-year-old artificial pigment that quantum physicists are trying to understand

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Han purple is an artificial pigment created by the Chinese over 2,500 years ago, which was used in wall paintings and to decorate the famous terracotta warriors, as well as ceramics, metal ware, and jewelry. The pigment is a technological wonder, made through a complex process of grinding up raw materials in precise proportions and heating to incredible temperatures. So intricate was the process, that it was not reconstructed again until 1992, when chemists were finally able to identify its composition. But this was just the beginning. According to a news report on, research since then has discovered amazing properties of Han purple, including the ability to emit powerful rays of light in the near-infrared range, as well as being able to collapse three dimensions down to two under the right conditions.

The production of Han purple, otherwise known as Chinese purple, dates back as far as 800 BC, however it appears that it was not used in art until the Qin and Han dynasties (221 BC – 220 AD), when it was applied to the world famous terracotta warriors , as well as ceramics and other items. 

“Prior to the nineteenth century, when modern production methods made synthetic pigments common, there were only hugely expensive purple dyes, a couple of uncommon purplish minerals, and mixtures of red and blue, but no true purple pigment – except during a few hundred years in ancient China,” writes Samir S. Patel in ‘ Purple Reign: How ancient Chinese chemists added color to the Emperor’s army ’.

For an unknown reason, Han purple disappeared entirely from use after 220 AD, and was never seen again until its rediscovery by modern chemists in the 1990s.

Traces of Han purple can still be seen on many of the terracotta warriors

Traces of Han purple can still be seen on many of the terracotta warriors (

The Synthesis of Han Purple

Unlike natural dyes, such as Tyrian purple (from c. 1500 BC), which are organic compounds and typically made from plants or animals, like the murex snail, Han purple was a synthetic pigment made from inorganic materials.

Only two other man-made blue or purple pigments are known to have existed in the ancient world – Maya blue (from c. 800 AD), made from a heated mixture of indigo and white clay, and Egyptian blue, which was used throughout the Mediterranean and the Near and Middle East from 3,600 BC to the end of the Roman Empire. [Read similar: Egyptian Blue – The Oldest Known Artificial Pigment ].

Scientist Elisabeth FitzHugh, a conservator at the Smithsonian, was the first to identify the complex synthetic compound that makes up Han purple – barium copper silicate, a compound that differs from Egyptian blue only through its use of barium instead of calcium.

"Egyptian blue" tripodic beaker

"Egyptian blue" tripodic beaker ( Wikimedia). The composition of Han purple differs from Egyptian blue only in the use of barium instead of calcium.

The similarities between Han purple and Egyptian blue led some early researchers to conclude that the Chinese may have learned to make the pigment from the Egyptians. However, this theory has been largely discounted as Egyptian blue was not found further East than Persia.

“There is no clear reason why the Chinese, if they had learned the Egyptian formula, would have replaced calcium with barium, which necessitates increasing the firing temperature by 100 degrees or more,” writes Patel.

So how exactly did the Chinese stumble upon the intricate formula to make Han purple, which involved combining silica (sand) with copper and barium in precise proportions and heating to about 850-1000 °C? A team of Stanford physicists published a paper in the Journal of Archaeological Science ( summary here ), which proposes that Han purple was a by-product of the glass-making process, as both glass and the purple pigment contain silica and barium. writes that barium makes glass shinier and cloudy, which means this pigment could be the work of early alchemists trying to synthesize white jade.

Fluorescent properties

Since its composition was first discovered, scientists have continued to investigate this unique pigment. Researchers at the British Museum discovered that, when exposed to a simple LED flashlight, Han purple emits powerful rays of light in the near-infrared range. According to their study, published in the journal Analytical and Bioanalytical Chemistry , the Han purple pigments show up with startling clarity under the right conditions, meaning that even faint traces of the color, which are invisible to the naked eye, can be seen with infrared sensors.

A Western Han ceramic bowl from Hebei or Hanan province

A Western Han ceramic bowl from Hebei or Hanan province (Avery Brundage Collection,, which contains traces of Han purple. The purple pigment becomes strongly fluorescent under infrared sensors (right).


love this stuff.

Tsurugi's picture

So....I take it these properties of the pigment are assumed to be accidental?

As in, someone in ancient China accidentally made high-efficiency infrared-reflecting dimension-collapsing quantumpaint?

Well, no. They just made some purple dye. We spotted the bonus features. Which don't really have any functional uses, they're just really interesting. 

Tsurugi's picture

In other words, yes. They accidentally made high-efficiency infrared-reflecting dimension-collapsing quantumpaint.

"It has no functional uses," hah. Quantum physicists are still trying to understand it and you're in here claiming it has no functional uses. I love your habit of making definitive statements on things you know absolutely nothing about.

Quantum effects aside, if you can't think of any functional uses for a paint that is highly reflective in the near infrared, your imagination must be horribly atrophied.

Bite me. These are just comments, old bean. They didn't accidentally find anything other than what they wanted: a nice purple colour. You have to do modern stuff to it for the effects. And if I need some IR reflective paint, I'd have to think twice about the cost of a pot of something made in blast furnace conditions as opposed to something synthetic and (poetically) mass produced in China. I really can't see it being daubed on aircraft carriers anytime soon as a camouflage or used in insulation as the main properties seem to be with light. And I'm not going to be that fussed if someone who thinks "rock" might transport you to another dimension, wants to throw me a condescending "hah". Stop being so serious. No one from Stanford is going to contact any of us for suggestions about what to do to it next.


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