Silk

Kinu

Silk has played an essential role in Japan’s culture, fashion, industry, and economy for centuries, and was already a major export even before its production was industrialized. As the manufacturing process evolved, Japanese silk gained increasing global recognition as a high-quality product. From small farms to life at the imperial court, silk was prominent in everyday Japanese life and proved crucial to the nation’s trade relations with the West. Gunma Prefecture leads Japan in the number of sericulturists and in raw silk production.

When Japan opened its doors to the Western world, the newly established Meiji government designated raw silk as the country’s primary export item. With the Meiji Restoration (1868), aiming to establish Japan as a modern nation and increase wealth by promoting new industries, factories were built by the government, such as the Tomioka Silk Mill in Gunma, constructed between 1871 and 1872. Large-scale production in a complex approximately 140 meters (459 feet) long that housed hundreds of machines made it the largest silk factory in the world at that time. 

After 115 years of raw silk production, the factory ceased operations in 1987, but it was preserved and registered as a UNESCO World Heritage Site in 2014. In addition, the spinning complex and the cocoon warehouses were designated as National Treasures of Japan.

Silk production involves several stages, beginning with sericulturists feeding silkworms (Bombyx mori) with mulberry leaves. Once they reach full growth, the silkworms stop feeding and become translucent. They are then removed from the feeding trays and transferred to structures made of cardboard, straw, or bamboo called mabushi. In these structures, they continuously spin their cocoons for 2 or 3 days. While spinning the cocoon, the silkworm caterpillar secretes a gummy protein called sericin, along with a filamentous protein called fibroin. Sericin acts as a glue, binding the fibroin threads to form the cocoon. The hatching occurs in about ten days: the moth attempts to emerge from the cocoon by boring a small hole in its surface. Once the cocoon is broken, it is not possible to obtain a continuous strand of raw silk; therefore, one of the most common ways to preserve the cocoons to maintain the continuous filament is to place them in boiling water. This process softens the inner and outer walls of the cocoon, partially dissolving the sericin. The continuous filament of raw silk measures approximately 900 to 1,500 meters (about 3,000 to 5,000 feet).

The finished silk threads are organized into portions folded or wound into many turns, known as skeins, to proceed to the weaving stage.

Silk fabrics are known for their unique luster, due to the triangular shape of the fiber that acts as a prism refracting light. The shade of raw silk before bleaching is called neri-iro (練色), a yellowish white that represents the natural color of the thread. The word shironeri (白練), on the other hand, is used to refer both to white silk and to a color—a lustrous white tone like silk.

Technical advice provided by Kazuyuki Natori, President of the Japan Color Research Institute (General Incorporated Foundation), and Shoko Isawa, former professor at Tokyo Kasei Gakuin University and Ph.D. in Engineering.

Source: Special Color Dictionary Wonderful & Beautiful 888. Supervised by Teruko Sakurai. Published by Tokyo Shoseki.