Making Han Purple — Ancient China's Synthetic Barium Copper Silicate Pigment

Han purple (BaCuSi₂O₆) is a synthetic barium copper silicate pigment produced in China from approximately 800 BC through the Han dynasty (206 BC–220 AD). Along with the closely related Han blue (BaCuSi₄O₁₀), it represents one of the earliest and most sophisticated examples of synthetic pigment chemistry — developed independently from Egyptian blue and using a fundamentally different flux chemistry based on lead rather than sodium.

The pigment was used to paint terracotta warriors, ceremonial bronzes, lacquerware, and tomb murals. Modern analysis of the Terracotta Army at Xi'an shows extensive use of both Han purple and Han blue. The chemistry requires barium carbonate (from the mineral witherite), a copper source (malachite), quartz sand, and lead oxide as a flux. These are ground together and fired at 900–1000°C for many hours. The lead oxide reduces the melting point and promotes the crystallisation of the barium copper silicate phase.

Han purple has a distinctive warm reddish-purple hue — deeper and more violet than Tyrian purple, with a crystalline sparkle when coarsely ground. It is reasonably lightfast but less stable than Egyptian blue — it slowly degrades in strongly acidic conditions.

SAFETY WARNING: This process involves HIGHLY TOXIC materials. Lead oxide (litharge) is extremely poisonous — it can be absorbed through skin and causes cumulative lead poisoning. Barium carbonate is toxic if ingested. The process requires kiln temperatures of 900–1000°C. Wear chemical-resistant gloves, goggles, and a P100 respirator. Work outdoors or in a fume hood. Never eat, drink, or smoke near lead compounds.