Women making Silk, 12th century
Silk fabric was first developed in ancient China, with legend giving credit for developing silk to a Chinese empress, Lei-zu. In July 2007, archeologists discovered intricately woven and dyed silk textiles in a tomb in Jiang-xi province, dated to the Eastern Zhou Dynasty roughly 2,500 years ago.
Although historians have suspected a long history of a formative textile industry in ancient China, this find of silk textiles employing complicated techniques of weaving and dyeing provides direct and concrete evidence for silks dating before the Mawangdui-discovery and other silks dating to the Han Dynasty (202 BC-220 AD).
Silks were originally reserved for the Kings of China for their own use and gifts to others, but spread gradually through Chinese culture and trade both geographically and socially, and then to many regions of Asia.
The Emperors of China strove to keep knowledge of sericulture secret to maintain the Chinese monopoly. Nonetheless sericulture reached Korea around 200 BC, about the first half of the 1st century AD had reached ancient Khotan, and by AD 300 the practice had been established in India.
Silk rapidly became a popular luxury fabric in the many areas accessible to Chinese merchants because of its texture and luster. Silk was in great demand, and became a staple of pre-industrial international trade.
The first evidence of the silk trade is the finding of silk in the hair of an Egyptian mummy of the 21st dynasty, c.1070 BC. Ultimately the silk trade reached as far as the Indian subcontinent, the Middle East, Europe, and North Africa. This trade was so extensive that the major set of trade routes between Europe and Asia has become known as the Silk Road.
Silk is a natural protein fibre, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture).
The shimmering appearance of silk is due to the triangular prism-like structure of the silk fibre, which allows silk cloth to refract incoming light at different angles, thus producing different colors.
Silks are produced by several other insects, but only the silk of moth caterpillars has been used for textile manufacturing. There has been some research into other silks, which differ at the molecular level.
A variety of wild silks, produced by caterpillars other than the mulberry silkworm have been known and used in China, South Asia, and Europe since ancient times. However, the scale of production was always far smaller than that of cultivated silks.
They differ from the domesticated varieties in color and texture, and cocoons gathered in the wild usually have been damaged by the emerging moth before the cocoons are gathered, so the silk thread that makes up the cocoon has been torn into shorter lengths.
Commercially reared silkworm pupae are killed by dipping them in boiling water before the adult moths emerge, or by piercing them with a needle, allowing the whole cocoon to be unravelled as one continuous thread. This permits a much stronger cloth to be woven from the silk.
Silk moths lay eggs on specially prepared paper. The eggs hatch and the caterpillars or silkworms are fed fresh mulberry leaves. After about 35 days and 4 moltings, the caterpillars are 10,000 times heavier than when hatched and are ready to begin spinning a cocoon.
A straw frame is placed over the tray of caterpillars, and each caterpillar begins spinning a cocoon by moving its head in a figure of eight pattern. Two glands produce liquid silk and force it through openings in the head called spinnerets.
Liquid silk is coated in sericin, a water-soluble protective gum, and solidifies on contact with the air. Within 2-3 days, the caterpillar spins about 1 mile of filament and is completely encased in a cocoon.
Harvested cocoons are then soaked in boiling water to soften the sericin holding the silk fibers together in a cocoon shape. The fibers are then unwound to produce a continuous thread. Since a single thread is too fine and fragile for commercial use, anywhere from three to ten strands are spun together to form a single thread of silk.
As the process of harvesting the silk from the cocoon kills the larvae, sericulture has been criticized in the early 21st century by animal rights activists, especially since artificial silks are available.