Han purple is an artificial pigment visible on old Chinese artifacts like pottery, and the Terracotta Army in the tomb of China’s first emperor, Qin Shi Huang.
It was created about 2,800 years ago in around 800 B.C., using a very precise inorganic recipe.
Also known as Chinese purple, this mysterious pigment has some unusual properties—it emits fluorescent light, and it can collapse three dimensions into two!
It was last used in 200 A.D., and then disappeared completely until modern-day chemists worked out its composition, and reconstructed it in 1992.
There are two other man-made blue or purple pigments: Maya blue, and Egyptian blue. The latter gains its color from calcium copper silicate, while Han purple’s is from barium copper silicate, suggesting the Chinese might have learned about it from the Egyptians.
But Stanford physicists believe it could have been produced while making glass or white jade, as both contain silica and barium.
Apart from its fluorescent properties, Han purple has an exotic magnetic behavior.
When exposed to extreme cold, and an intensely strong magnetic field, the pigment switches to a state called the quantum critical point where it “loses” its vertical dimension. This means that light waves traveling through it can only move in two dimensions, possibly due to the mineral’s tile-like structure.
So as well as intriguing archaeologists, and chemists, the pigment has been fascinating physicists too.