By 1200, Chinese elites began using flat smoky quartz lenses known as Ai Tai to shield their eyes from glare and to conceal their facial expressions during interactions. This innovation represented an early use of optical technology in society, reflecting the cultural importance of maintaining poise and decorum. The use of these lenses not only influenced fashion but also laid the groundwork for future developments in eyewear and optics.

Chinese smoky quartz Ai Tai lenses, developed around 1200, reflected in Chinese poetry and court literature, symbolizing impartiality and mystery. This innovation influenced the interplay of sight and hidden truth in poetic imagery, enriching the depth of literary expression in the region.