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Volume 39, Number 4July/August 1988

In This Issue

The Queen and the Silkworm
Written by Paul Lunde
Photographed by Stephen Dalton

Xiling Shi was strolling in the palace garden one day and passed under a mulberry tree, from one of whose leaves she idly plucked a white cocoon. Later, as she took her tea, she happened to drop the cocoon into her steaming cup, and, reaching in to fish it out, unraveled a long white thread.

Xiling was the wife of Huangdi, the semi-mythical emperor who ruled China in the middle of the third millennium BC. He is also credited with the invention of pictographic writing so, according to legend, he and his wife were responsible for the two most characteristic features of Chinese civilization: its script and its silk.

Silk cultivation is certainly very old in China, although not perhaps quite so old as legend has it. The Chinese ideograms for silk, silkworm and cocoon have been found inscribed on oracle bones that date back to the Shang dynasty of the second millennium BC.

By the time of the Zhou dynasty, which held power from the twelfth to the third centuries BC, the place of silk in the economy of China was securely established, as were the delicate and complex methods of its cultivation and manufacture. They have changed little since.

The silkworm, a caterpillar, is the larva of Bombyx mori, a heavy,flightless moth that is the only member of the order Lepidoptera domesticated by man. The caterpillar's preferred food is the large, broad leaves of the white mulberry tree, Morus alba, which has no fruit or flowers. The interlocking peculiarities of both tree and moth are presumably the result of thousands of years of human interference; like the banana or the saffron crocus, the silkworm does not exist in a wild state.

Timing is all-important in silk production, for the eggs that eventually become caterpillars must hatch at the same time that the mulberry trees begin producing leaves. When the first leaf buds appear, the eggs are removed from cold storage, where they have been kept for six to 10 months, and put in an incubator for 10 days. Finely chopped mulberry leaves are fed to the silkworms, which undergo four mutations in the 35 days after hatching, eventually reaching a length of about five to nine centimeters (2 to 3.5 inches). At this stage they consume 20 times their own weight in mulberry leaves.

The silkworms are transferred to bamboo racks and begin spinning their cocoons. Two pairs of glands in the silkworms' heads secrete a double filament of one liquid protein, fibroin, glued together by a different protein. The silk thread hardens on exposure to the air and, moving its head in a figure-eight pattern, the larva lays thread upon thread to build its oval cocoon in a few days. The racks must be dry and warm for this to be successful, for the silkworms are very sensitive to temperature changes, loud noises and even human scents.

Only enough moths are allowed to hatch to lay the next generation of eggs. The rest of the cocoons are steamed or plunged into boiling water to kill the pupa and then sorted, the whitest and most perfect being set aside for silk, while broken, damaged or discolored cocoons are used for padding or floss.

Special combs are used to remove the loose silk fluff on the outside of the cocoon; then the long, continuous inner thread is unwound, two or more threads being passed through porcelain guides and plied to form a stronger unit. Some 1,500 meters of silk filament (nearly one mile) can be unwound from a single cocoon, but the material is so fine that as many as nine cocoon filaments are needed to produce a 14-denier silk thread - one that weighs 14 grams per 9,000 meters of length (one-half ounce per 30,000 feet). It has been estimated that 30 mulberry trees are required to produce a kilogram (2.2 pounds) of silk.

Sericin, the protein "glue" of the silk filament, remains on the long fibroin strands during the processing of silk thread, protecting it from damage. Softened in oil or a soap solution, the plied threads are wound onto bobbins and may be plied again. Silk cloth containing sericin - originally about one quarter of the fiber by weight - is called raw silk; usually, however, the sericin is stripped from the thread or fabric with a hot alkaline wash after processing, leaving a soft and lustrous end product.

Silk is extremely durable - silk thread has greater tensile strength than steel - and if stored carefully lasts almost as long as metal. A Tang silk robe found in 1969 in a grave in the Caucasus - now in the Hermitage Museum in Leningrad - is in remarkably fine condition after some 1,300 years; even earlier fragments of silk found in Central Asia and Palmyra still retain their original gloss.

For the peoples of Central Asia and further west, silk was a miraculous fabric, light and strong, glossy and soil-resistant, susceptible of subtle dyeing and extremely long-lasting. How it was made and what it was made of were mysteries, and this added to the allure of silken fabrics. Today, we still feel the allure of this lovely material, woven from the threads so casually discovered by Xiling's carelessness: the filaments spun by a flightless moth.

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This article appeared on pages 2-5 of the July/August 1988 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for July/August 1988 images.