ai　藍

KEY WORD :　art history / paintings

Indigo. A plant of the polygonacede family from whose stems and leaves comes a blue dye and pigment for painting. Produced in southeast Asia and thought to have been imported to Japan from China from the 5c or 6c. In Japan, grown primarily in Tokushima prefecture. The process of producing a liquid indigo dye is known as aidate 藍建て. One of the earliest methods of extracting dye from the leaves consisted of adding water and passing the mixture through a cloth filter. The extract of this process was used to dye silk glossed with lye. From the Nara period, dyers fermented the indigo leaves in water before use, giving a deeper blue color. In the Kamakura period, dyers added woodash, lime, and other alkaline ingredients to facilitate fermentation, and, in the Edo period, dyers first composted the leaves and then fermented them in an alkaline solution. This provided two stages of fermentation, yielding a stronger color and acting to deter insects from the dyed cloth. Fermentation requires a temperature of around 30 celcius, and this limited the dyers' work to the summer season, but in the Edo period it became standard practice to sink the indigo pots in the ground and heat them, allowing work to continue throughout the year. When the composted leaves are dissolved in liquid, the bacteria in the organic material consume oxygen, and the indigo blue is reduced to indigo white. This adheres to dipped cloth, and turns blue again when air-dried. Depending on the number of times a fabric is dipped in the dye, different shades of blue result. These vary from a light blue, mizu-iro 水色, obtained after only one dip, through to dark blues, kon 紺 and kachi 褐 requiring ten to twenty dips. As each layer needs to be well dried before re-dipping, this process can take many weeks. Thin indigo is said to have a greenish tinge, and deep indigo tends to show a hint of purple. Indigo was used as a painting pigment, as well. Purple bubbles of oxidized indigo were skimmed off the top of the dye vat, dried, and pulverized. The powder was mixed with animal glue *nikawa 膠, and hardened to make indigo sticks, aibou 藍棒. To produce pigment for painting, the stick was rubbed with water on an inkstone. Indigo pigment can be seen on the murals at Daigoji Gojuu-no-tou 醍醐寺五重塔 and Byoudouin *Hououdou 平等院鳳凰堂 in Kyoto.

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