Silk is a protein filament extruded by the larvae of insects, most especially the silk moth Bombyx mori. The moth takes its name from the mulberry leaf on which the larvae feed (Morus is Latin for mulberry). Each larva creates two filaments (fibroin), stuck together by silk gum (sericin) to form its cocoon. The silk filament is reeled from cocoons after the larvae’s development has been stopped. (Some cultivated silk larvae are allowed to develop and emerge as moths for the next year’s egg production.) Warm water is used to loosen and unreel the filament fiber, which includes the gum as well as the silky filament at this stage. The gum is then removed by varying degrees, and at varying stages of production. Silk filament without gum is white; the gum gives the filament an ecru color. The filaments from a single cocoon of one silkworm are on average a mile long, and are strong, glossy and resilient.
Double cocoons, or ones that became intertwined when the larvae are spinning them, unreel unevenly, with thicker spots in the filament. This type of silk fiber is suitable for weaving doupioni silk, shantung and pongee, where the thick spots show as slubs in the texture.
The silkworm moth, Bombyx mori, can’t now survive in the wild after being domesticated for such a long time; it is neither camouflaged nor able to fly. Silk fabric is also produced from wild moth larvae, most notably those of the tussah moth. This wild silk is of a very different style and quality.
In the long history of silk culture (sericulture), China has always been king. The use and cultivation of silk dates from at least 2500 B.C.E. there. The lucrative silk trade reached India, Europe, Africa, the Middle East and North Africa along what was known as “The Silk Road,” beginning during the Han Dynasty (around 200 B.C.E.). For centuries China carefully guarded its silk production method. Silk cultivation was smuggled into Byzantium ca. 550 C.E., and by the 14th and 15th centuries Italy had become known for its fine silks, followed not long after by France and England. At this point China is by far the largest producer of silk, and this not only follows from China’s history of production but also from its relatively large low-wage work force—silk production is labor intensive.