Indigo refers to several plants, all of which dye blue, but in Japan the most common is ai (also called tadeai), Polygonum tinctorium Lour, a relative of buckwheat. In the Nara period, fresh indigo leaves were used to dye light blue or placed in a deep vat and fermented to dye deeper blues. The Repository has indigo-dyed silk, bast-fiber cloths, and paper.