Archaeologists in Shaanxi Province have excavated a subterranean bunker belonging to the Han Dynasty Imperial Bureau of Textile-Dye Standardization. The site yielded a remarkable collection of carbonized silk-swatches, each accompanied by a wooden slip detailing the exact botanical proportions of madder, indigo, and gardenia used to achieve specific imperial shades of red, blue, and yellow.
This 'color library' was used to ensure that officials across the empire wore standardized uniforms that correctly reflected their rank according to the Han sumptuary laws. The discovery of copper-sulfate mordants in situ provides evidence of the chemical precision required to fix colors in large-scale industrial vats. These findings rewrite the history of Han chemical engineering, proving that the empire maintained a centralized registry for aesthetic and industrial consistency across its vast textile networks.