2,800-Year-Old Han Purple – The Wonder of Ancient Technology

by Sankalan Baidya

Ancient people were not very technologically advanced. That is what we usually think but the careful study of Han Purple proves us to be completely wrong. The ‘Han Purple’ gives us a fair idea of the place of origin of whatever this thing is, right? Yes, you guessed pretty accurately. It is a Chinese creation!

Han Purple is the name given to a synthetic pigment produced in China way back in time. Roughly, the pigment was produced 2,800 years ago. What makes this pigment is technological marvel of the ancient times is its surprising magnetic effects, not to mention the preparation method which is extremely complete and requires extreme technical precision – something that requires help of highly advanced technology to achieve in today’s context.

Complexity of Han Purple

The first step of Han Purple preparation requires grinding the raw materials in precise proportions. Even a minor error in measurements will not produce the desired end product. Once the raw materials are ready, the grinded mixture requires extreme heating at a temperature ranging between 850˚C to 1000˚C. Achieving such high temperatures back in those days required highly advanced scientific knowledge.

Let us try and explain the level of complexity involved in Han Purple production using timeline. This artificial pigment using chemicals was first produced somewhere back in 800 BCE. Back then it was not used extensively for art until the rise of the Qin Dynasty and Han Dynasty between the period 200 BCE and 220 CE. The pigment was used extensively during the Han Dynasty rule which is where the pigment gets in name from. 220 CE was the last time the pigment was used after which it simply vanished either because people didn’t know it existed or people could not replicate the production process. Finally, the Han Purple (or sometimes referred to as Chinese Purple) was rediscovered in 1990s and first successful replication took place in 1992 after the scientists eventually managed to figure out the chemical composition of the pigment.

Other manmade purple pigments

In ancient times only two other manmade purple pigments were in use. One was Egyptian Blue, which is the oldest known manmade pigment and the Maya Blue. Egyptian Blue was first synthesized roughly around 3,600 BCE and was in extensive use in areas close to Middle East, Middle East and Mediterranean. This pigment was extensively used until the very end of the Roman Empire. The Maya Blue on the other hand was first synthesized roughly around 800 CE.

The Maya Blue was produced by heating a mixture of white clay and indigo but the Egyptian Blue was slightly more complex and was produced by mixing and heating silica, copper and calcium.
Initially it was though that the Chinese people borrowed the Roman knowhow of synthesizing purple pigment but this notion was shattered with Smithsonian’s conservator, scientist Elizabeth FitzHugh identified a different chemical composition of the Han Purple. It was found that the Chinese made the pigment using silica, copper and barium (instead of calcium used by the Romans).

The big question about Chinese Purple

Even if it was assumed that the Chinese borrowed the Roman formula, it really did not make any sense as to why they would replace calcium with barium and unnecessarily increase the heat required for the synthesis? So the question that really started puzzling experts is: how exactly the Chinese stumble upon the idea of combining barium, copper and silica? To answer this question, Stanford physicists stepped forward and published a paper in which they theorized that the pigment was just a byproduct of the process of making glass. The physicists came up with this theory because according to them, both the pigment and glass contains both barium and silica. io9.com on the other hand says that the pigment was possibly an outcome of ancient alchemic quests because according to the website, barium is known to give glass cloudy and shinier look which simply means that possibly, early alchemists tried synthesizing white jade. Despite the different theories that have been put forward, we still don’t know exactly how the Chinese came up with the idea of synthesizing Han Purple and possibly, we will never know.

The amazing properties of Han Purple

The pigment has fluorescent properties

British Museum’s researchers decided to investigate the properties of the pigment and the simple thing they did was that they placed the pigment underneath LED flashlight and they immediately found the pigment emitting powerful light in near-infrared region. They found that under right conditions, the pigment is capable of giving amazing clarity. This simply means that naked eyes fail to see faint traces of pigment, it becomes visible under infrared sensors.

The pigment can become 2D from 3D

Stepped in a group of scientists from University of Tokyo’s Institute for Solid State Physics and Quantum physicists from Los Alamos National Laboratory. After careful studies, these scientists found that when pigment is subjected to high magnetic field and extreme cold, the pigment reaches quantum critical point where it loses one dimension. In simple words, the 3 dimensional structure of the pigment becomes 2 dimensional. So why exactly the pigment loses a dimension? According to scientists who studied the pigment, the barium copper silicate components have a layered arrangement with subsequent layers not being stacked properly, i.e. they are slightly out of sync and as a result of it, when subjected to right conditions (i.e. magnetic field 800,000 times stronger than Earth’s magnetic field and temperature below 1˚Kelvin), frustrating the magnetic wave traveling in 3D dimension, which then forces the pigment to lose one dimension. The magnetic wave then loses its vertical component and travels only in two dimensions!

Expert speaks about Han Purple

Ian Fisher, Stanford’s assistant professor of Applied Physics says: “We have shown, for the first time that the collective behavior in a bulk three-dimensional material can actually occur in just two dimensions. Low dimensionality is a key ingredient in many exotic theories that purport to account for various poorly understood phenomena, including high-temperature superconductivity, but until now there were no clear examples of ‘dimensional reduction’ in real materials.

Uses of Han Purple

Han Purple in ancient times was used primarily for art. It was widely used in jewelry, metal ware, ceramics and wall paintings. However, the most popular use of this pigment was to put colors on the famous terracotta warriors from the Han Dynasty.

Sources: 1, 2, 3, 4

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