The Three-Color Botanical Pharmacy
The traditional silk fabric of Hachijō-jima island, known as Kihachijō, relies on a palette of just three colors derived entirely from local plants. Each color requires a specific botanical source and a multi-day chemical process involving repeated dyeing and sun-drying to achieve its characteristic luster. The entire process is an application of textile chemistry, perfected over centuries.
The signature yellow that gives Kihachijō ("yellow Hachijō") its name comes from the grass Arthraxon hispidus. Weavers boil the dried grass for hours to create a dyebath. Silk threads are soaked in this hot decoction overnight, then wrung out and dried in the sun. This cycle of soaking and drying is repeated approximately 15 to 20 times to build up a deep, lasting color.
The reddish-brown color, called Tobi-hachijo, is extracted from the bark of the Machilus thunbergii tree, a type of laurel. For the black dye, or Kuro-hachijo, weavers use the bark of the Castanopsis cuspidata, an evergreen tree related to the beech. The process for black is even more intensive, requiring the dyeing and drying cycle to be repeated as many as 40 times.
Mordants: Ash, Iron, and Mud
A dye is not truly fixed to a fiber until a mordant is applied. A mordant is a substance that forms a chemical bridge between the dye molecule and the fiber molecule. On Hachijō-jima, the mordants are as locally sourced as the dyes.
For the yellow-dyed threads, the important mordanting agent is a lye made from the ash of camellia (Camellia japonica) and sakaki (Cleyera japonica) trees. The weaver rubs this alkaline solution into the dyed silk skeins 50 to 60 times. The alkalinity of the wood-ash lye helps to chemically bond the dye compounds to the silk protein fibers, ensuring the color's permanence.
The black dye requires a different chemical reaction. After being dyed with Castanopsis bark, the silk threads are taken to a specific iron-rich marsh on the island. The threads are submerged in the mud, a technique called dorotsuke (mud-mordanting). The iron compounds in the mud react with the tannins from the tree bark, creating a deep, permanent black. This use of iron-rich mud as a mordant is a distinctive feature of the island's dyeing tradition. The combination of plant-based dyes and unique mordants results in a fabric whose colors are known to become more vivid with washing and age.