Silk (Sīchóu 丝绸)|Sīchóu 丝绸 (Silk)

Paul FORAGE

Mulberry leaves used to feed silkworms. PHOTO BY PAUL AND BERNICE NOLL.

Silk production in China has evolved for thousands of years but remains tied to the life cycle of the silkworm and its sole diet of mulberry leaves. Silk was such an important product during ancient times that the major trade route between East Asia, West Asia, and Europe was called the “Silk Roads.” Its status as a luxury item remains the same today, and China continues to be the world’s largest silk producer.

Although the exact origins of sericulture (the production of raw silk from silkworms) are not known, experts agree that it began in China about 2500 BCE. Chinese mythology supports this date. In one popular myth the empress of a legendary emperor is credited with intensifying mulberry tree cultivation, breeding and raising silkworms, and inventing the loom in 2640 BCE. This myth also is important because it acknowledges the major role that women played in silk production and processing.

Production of silk was a vital part of the rural economy, and through the centuries many technical advances speeded up the production of silk thread. However, weaving remained difficult and time consuming until the invention of mechanized looms in the twentieth century. Although silk was produced mostly in rural areas, it was usually woven in urban centers for the imperial court or for well-to-do city dwellers, and people often paid raw silk cloth as taxes to the central government.

In about 140 BCE, during the Han dynasty (206 BCE–220 CE) silk production spread from China to India and to Japan a few centuries later. It spread to Europe in about 550 CE (during China’s Southern and Northern Dynasties period, [220–589 CE]) when the Byzantine Emperor Justinian I asked two Persian monks to smuggle silkworms from China. In fact, silk was such an important product during ancient times that the major trade route between East Asia, West Asia, and Europe was called the “Silk Roads.” The Chinese traded silk for gold, silver, and wool.

China at the beginning of the twenty-first century remains the world’s major producer of silk, accounting for about 80 percent of the world’s silk. However, the development of synthetic fibers such as rayon (beginning in 1910) and nylon (beginning in the late 1930s) has decreased the demand for silk clothing. As it was in ancient times, silk continues to be a luxury item but is no longer a major export for China.

Silkworm Life Cycle

The life cycle of the silkworm (Bombyx mori) largely determines silk production. Silkworm caterpillars hatch from eggs and need large amounts of mulberry leaves for food. Their growth period lasts from thirty-four to thirty-five days and is interrupted by several periods of dormancy. At the end of this period of growth, the caterpillars spin cocoons of a single strand of silk thread that can be from 600 to 900 meters long.

The adult moths, under natural conditions and uncontrolled by humans, would then emerge from the cocoons and reproduce. However, for silk production the emergence of the moth from the cocoon would be a disaster: The emerging moth breaks the silk strand and renders it virtually useless for cloth production. Thus, most moths are killed while still in the cocoon, although a few are allowed to reach maturity for breeding purposes.

Mulberry Tree Cultivation

Most phases of the life cycle of the silkworm are controlled by careful regulation of mulberry leaves (the silkworm’s sole food) and temperature. In early times mulberry trees were planted in orchards, and new varieties were developed. The most crucial development had occurred by the twelfth century, with perfection of a method of grafting a leafy variety of tree onto the trunk of a hardier variety. Agricultural treatises of the twelfth century describe the method and suggest that silk producers everywhere adopt it. Use of such grafts permitted two crops of leaves a year in the central region of China and three in the southern regions.

Controlling the Process

Providing the silkworms with leaves was always of great importance, and in the fifth century a method was invented to regulate the hatching time of silkworm eggs to coincide with maximum leaf production. The eggs were bathed in cold water to lower their temperature and to delay hatching, often for as long as twenty-one days. The addition of periods of warming and cooling during the thirteenth century improved the method and had the extra advantage that eggs that contained malformed or weak worms could not survive the changes in temperature. After the eggs hatched growers found it best to have the worms grow as quickly as possible, and thus various techniques for warming the growing sheds were devised. During the sixth century fires of burning manure were generally used, although such fires sometimes produced unwelcome smoke. By the twelfth century small portable stoves had been invented. They warmed the sheds without producing smoke and could be removed if necessary. Large-scale silkworm operations often had large fire pits in the growing sheds. Such fires would be lit five to seven days before the eggs hatched and were left to warm the sheds during the growth phase of the worms. With these methods the growth phase of the silkworms could be reduced to just twenty-nine to thirty days.

Reeling the Thread

Reeling the silk fibers of the cocoons into thread was preferable while the moths were still alive in the cocoons because doing so produced a higher quality of silk, but this technique was impracticable because it was so labor intensive. Because most silk thread was produced by small rural operations that lacked large workforces, the moths were killed before they could damage their cocoons. Three methods commonly used to kill the moths were leaving the cocoons out in the sun, salting them, and steaming them in ovens. By the nineteenth and twentieth centuries, when mass production began, steaming became the most common method.

Reeling the thread involves unraveling the cocoons and twisting several fibers together to form a thread and then winding the thread onto a reel. This process can be done by hand, but by the late eleventh century a treadle-operated reeling frame had been devised. It allowed one person to reel large amounts of yarn relatively quickly. The design of the frame took into account the qualities of silk. The cocoons were placed into a basin of heated water because water loosened the fiber in the cocoons. The heat caused the fibers to move and twist of their own accord. The motion of the water caused the threads to be more rounded. However, despite this technical advance, silk reeling required constant labor after it was begun and was difficult and time consuming.

Weaving Technology

Weaving lent itself less readily to improvements. The reeled yarn had to be made into the warp (a series of yarns extended lengthwise in a loom and crossed by the weft) and weft (a filling thread or yarn in weaving) by a spindle wheel. Preparation could take days. Two people were needed to operate the loom to weave just plain silk, and if elaborate designs were to be added, the production of even small quantities of cloth could take weeks. Early silk-weaving operations were run by weaving families who worked from their own homes, and many of the practices were passed down for hundreds and hundreds of years with little change. Technological innovation in silk production
reached its zenith during the Song dynasty (960–1279), but not until the founding of the first modern silk-weaving factory in 1905 in Hangzhou was the silk industry further transformed.

The silk cloth, after it was woven, could be left raw, or it could be “finished” by being boiled in a solution of ash, steeped in soap overnight, and rinsed to render it softer. Many peasants produced silk to pay taxes and thus left the cloth raw.

Silk in Society

Much production of silk took place in rural areas, but complicated designs were usually woven in urban workshops or imperial factories that produced elaborate luxury goods for aristocrats, the imperial court, or wealthy city dwellers. Silk was a luxury, and it was jealously guarded by the imperial court, which often stockpiled bolts of silk instead of precious metals. During the Song dynasty, when foreign invasion threatened the imperial government, silk was an important diplomatic tool, with millions of bolts of cloth paid in tribute during the eleventh and twelfth centuries. Rulers also used silk to reward outstanding acts, to pay government officials, and to give relief to victims of disasters.

Use of silk in everyday dress was strictly regulated by sumptuary (relating to personal expenditures and especially extravagance and luxury) law. Laws were also enacted against the use of gold thread, garments of certain colors, “foreign” styles of dress, and embellished silk. Certain patterns were reserved for the imperial court. Although penalties such as caning and jail sentences were meted out, these laws seem to have been largely ignored by people who were wealthy enough to afford luxury items. Enemies of the Chinese were also aware of the prestige attached to clothing because they often asked for certain grades of silk cloth with decorations reserved for the imperial family as tribute.

Further Reading

Nakayama, S., & Sivin, N. (Eds.). (1973). Chinese science: Explorations of an ancient tradition. Cambridge, MA: MIT Press.

Temple, R. (1986). The genius of China: 3,000 years of science, discovery, and invention. New York: Simon & Schuster.

Yoke Ho Peng. (1985). Li, qi and shu: An introduction to science and civilization in China. Seattle: University of Washington Press.

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