Journal

How Natural Indigo
Ages Differently from Indigo

Natural indigo and indigo. Both are blue, yet their origins and the way they age over time are different. Natural indigo is born from a plant and becomes a dye through a long process of fermentation. Indigo, on the other hand, is applied through rope dyeing, coloring only the outer layer of the yarn. The difference lies in how they penetrate the fiber, and how time reveals their character. For us, what matters is not which is superior, but that both are blues that grow more beautiful with time.

Indigo is rope-dyed, coloring the outer layer of the yarn while leaving the core untouched. Because the center remains white, wear and washing gradually reveal contrast, creating the dimensional fades that define denim. This “white core” structure is what allows denim to develop strong, personal character over time. Our indigo is not simply a standard, ready-made dye. We were captivated by the deep tone of natural indigo and have continually asked ourselves how that blue could be expressed through indigo dyeing. The depth of color, the way it fades, and the way it will age over years of wear are all carefully considered when formulating our dyes. Since 1991, we have continued to refine our research, and today we create approximately 35 original indigo recipes. Names such as R66, Kageironando, Ainando, R45, and Ruri, which appear as color names on our products, refer to these distinct indigo formulations. Blue is never just one shade; each recipe carries its own way of maturing.

Natural indigo begins with planting the seeds of Persicaria tinctoria. Seeds are sown in spring, leaves are harvested in summer, dried, and then fermented to create “sukumo,” the base material for dye. This stage alone takes close to a year. Sukumo is then placed in fermentation vats, where microorganisms reduce the dye to a usable state. Temperature and moisture must be carefully managed every day as the dye slowly develops. The dyeing itself is repeated many times: fabric is immersed, exposed to air to oxidize, then immersed again. Through these repeated cycles, the blue gradually deepens. Unlike indigo, natural indigo carries a distinct clarity. Its blue feels purer and stronger, yet at the same time softer. In light, it reveals a quiet depth and transparency unique to plant dye. From seed to finished cloth, the process takes at least a year. The time spent working alongside nature is what gives natural indigo its calm strength. At 45R, products labeled with “Ai” in their name are made using natural indigo. Even within denim, the quality of time embedded in the fabric is different.

Natural indigo and indigo differ in how they are dyed and how they age. Yet what we continue to pursue is the same: a blue that becomes more beautiful with time. Captivated by the depth of natural indigo, we have continued exploring how to express that blue through indigo dyeing. Our approximately 35 original recipes are part of that ongoing pursuit. Denim, for us, is a staple.

Something to wear every day, and still cherish ten years from now. Within this never-finished craft, 45R’s blue will continue to grow.