The Yoshino River valley in Tokushima was once Japan's largest indigo-producing region, supplying the blue that dyed the cotton worn by most of the country during the Edo period. The wealth generated by this trade is visible in the merchants' houses that still stand along the river. The indigo trade collapsed with the introduction of synthetic dyes in the Meiji era, but the tradition of natural indigo cultivation and dyeing has survived in Tokushima as nowhere else in Japan. The dyeing workshops available in Tokushima City use genuine natural indigo — not synthetic approximations, but the fermented leaf of the tade ai plant that has been processed in the traditional way. The color it produces is different from synthetic indigo in ways that are visible and tactile: deeper, more varied, alive to light in a way that changes with the hour and the angle. The cloth also changes over time, the color deepening with wear and washing in a manner that synthetic dyes do not replicate. The moment of dyeing is worth experiencing for itself: the cloth enters the vat greenish, and as you lift it into the air and the oxygen reaches the fiber, it turns blue. This chemical reaction — the conversion of leuco-indigo to indigo upon exposure to oxygen — is the same process that has been producing this color for thousands of years. Watching it happen in Tokushima, in a tradition that has been doing it here for centuries, is one of those experiences that makes chemistry and history briefly indistinguishable.