Silk​—“The Queen of Fibers”

BY AWAKE! WRITER IN JAPAN

SOME of the most beautiful garments in the world​—including the Japanese kimono, the Indian sari, and the Korean hanbok—​have something in common. Often, they are made of silk, a lustrous fabric that has been called the queen of fibers. From royalty of the past to commoners of the present, people worldwide have been captivated by the elegance of silk. But it has not always been so widely available.

In ancient times the production of silk was an enterprise exclusive to China. No one else knew how to produce it, and anyone in China who divulged the secret of the silkworm could be executed as a traitor. Not surprisingly, this monopoly on manufacturing made silk quite expensive. Throughout the Roman Empire, for example, silk was worth its weight in gold.

In time, Persia came to control all silk coming out of China. The price was still high, though, and efforts to bypass Persian merchants proved futile. Then, Byzantine Emperor Justinian devised a plan. About 550 C.E., he sent two monks on a covert mission to China. Two years later they returned. Concealed in the hollow of their bamboo canes was the much-awaited treasure​—silkworm eggs. The secret was out. The silk monopoly came to an end.

The Secret of Silk

Silk is produced by silkworms, or caterpillars of the silkworm moth. There are hundreds of types of silkworms, but the scientific name of the one that produces the finest quality silk is Bombyx mori. It takes quite a number of silkworms to make silk fabrics, which has given rise to sericulture, the raising of silkworms. The family of Shoichi Kawaharada, who live in Gunma Prefecture, Japan, is one of approximately 2,000 households in this country still engaging in this labor-intensive work. His two-story house, ideally built for sericulture, is situated on the side of a hill overlooking a mulberry grove (1).

The female silkworm moth lays up to 500 eggs, each of them the size  of a pinhead (2). After about 20 days, the eggs hatch. The tiny silkworms have an insatiable appetite. Night and day they eat mulberry leaves​—and only mulberry leaves (3, 4). In just 18 days, the silkworms will have grown to 70 times their original size and will have shed their skin four times.

Some 120,000 silkworms are raised on Mr. Kawaharada’s farm. The sound of them feasting creates a noise not unlike the sound of heavy rain falling on leaves. By the time a silkworm is grown, its weight will have multiplied by 10,000! Now it is ready to spin a cocoon.

Silent Spinners

At full growth the body of the silkworm turns translucent, signaling that it is time to start spinning. When the silkworms become fidgety and begin looking for a place to nestle their cocoons, they are ready to be mounted onto a cubicle with many square openings. There, they eject their fine, white thread (5), encasing themselves in silk.

This is the busiest time for Mr. Kawaharada, since all 120,000 silkworms start spinning at approximately the same time. Rows and rows of cubicles are hung in the cool, ventilated loft on the second floor of the house (6).

Meanwhile, an amazing change is taking place inside the silkworm. Digested mulberry leaves have turned into fibroin, a type of protein that is stored in a pair of glands that run the entire length of the caterpillar. As the fibroin is pushed through these glands, it is coated with a gumlike substance called sericin. Before coming out of the spinneret, located at the  worm’s mouth, two fibroin fibers are stuck together by the sericin. Upon contact with the air, this liquid silk solidifies to form a single filament.

Once the silkworm starts churning out silk, there is no stopping it. The silkworm spins at a speed of between 10 and 15 inches [30-40 cm] a minute, all the while swinging its head. One source estimates that by the time the cocoon is completed, the silkworm will have swung its head some 150,000 times. After spinning for two days and two nights, the silkworm will have produced a single thread measuring up to 5,000 feet [1,500 m] in length. That is about four times the height of a tall skyscraper!

In just one week, Mr. Kawaharada will have harvested his 120,000 cocoons, which will then be shipped for processing. It takes about 9,000 cocoons to make a kimono and about 140 to make a tie, while a silk scarf may require more than 100.

How Silk Fabric Is Made

The process of unwinding silk from a cocoon onto a reel is called reeling. How did silk reeling get started? Myths and legends abound. One has it that the Chinese Empress Hsi Ling-Shi noticed that a cocoon had fallen from a mulberry tree into her cup of tea. Trying to retrieve it, she saw that it came out on a delicate silk thread. This gave birth to reeling, a process that today is automated.

For the cocoons to have market value, the pupas inside them must be killed before they can hatch. Heat is applied to accomplish this grim task. Defective cocoons are sifted out, and those that remain are ready to be processed. First, cocoons are put in hot water or steam to loosen up the filament. Then, the start of the filament is caught with revolving brushes (7). Depending on the thickness desired, filaments from two or more cocoons may be combined to form a single yarn. The yarn is dried as it is wound on a reel. The raw silk is reeled again, onto a larger reel, to form a skein of desired length and weight (8, 9).

You may have felt silk fabric so smooth and supple that you almost wanted to stroke your cheeks with it. What determines its distinct texture? One factor is the degumming, or removal, of sericin, which coats the fibroin. Silk that has not been degummed feels coarse and is hard to dye. Chiffon fabric has a grainy texture, since some of the sericin remains.

The second factor is how much turn, or twist, the yarn gets. Japanese habutai fabric has a soft, smooth touch. It has little or no twist. In contrast, crepe fabric has a crispy, crinkly texture. It has a strong twist.

Dyeing is another important process. Silk is easy to dye. The structure of fibroin allows dyes to penetrate deep, resulting in excellent colorfastness. In addition, unlike synthetic fibers, silk has both positive and negative ions, meaning that virtually any dye will produce good results. Silk can be dyed as a yarn before it is woven on a loom (10) or as a piece of fabric afterward. With the famous yuzen dyeing of kimonos, beautiful motifs are drawn and dyed by hand after the silk is woven.

While most silk production is now done in countries such as China and India, haute couture of France and fashion designers of Italy still lead the world in silk designs. Today, of course, artificial fibers such as rayon and nylon provide the apparel market with many inexpensive fabrics. However, silk still has no equal. “Even with the present advancement in science, silk cannot be synthesized,” says the curator of the Silk Museum in Yokohama, Japan. “We know everything, from its molecular formula to its structure. But we cannot copy it. That is what I call the mystery of silk.”

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QUALITIES OF Silk

Tough: Silk is as strong as steel filament of comparable size.

Lustrous: Silk has an elegant luster of pearl. This comes from the multilayered, prismlike structure of fibroin, which diffuses light.

Gentle to skin: The amino acids that make up silk are gentle to the skin. Silk is said to guard against various skin-related ailments. Some cosmetics are made from silk powder.

Moisture absorbent: The amino acids and the tiny voids in silk fiber absorb and let out a considerable amount of perspiration, keeping you dry and cool in the hot season.

Heat resistant: Silk does not burn easily and does not give off toxic gas in the event of fire.

Protective: Silk absorbs ultraviolet rays and thus protects the skin.

Not prone to static-electricity buildup: Since silk contains both positive and negative ions and is moisture absorbent, it does not readily form static electricity, as some other fabrics do.

CARING FOR Silk

Washing: It is usually best to have silk garments dry-cleaned. If washing at home, use neutral detergent in warm water (at about 85 degrees Fahrenheit [30°C]). Be gentle, and do not knead or wring the fabric. Let it air dry.

Ironing: Place a cloth between the iron and the silk. Try to iron in the direction of the grain at a temperature of about 260 degrees Fahrenheit [130°C]. Use only a small amount of steam, if any.

Removing soil: As an emergency measure, place the silk fabric facedown on a dry piece of cloth. Beat, not rub, from the back with a moist cloth. Then have the item dry-cleaned.

Storing: Avoid humidity, guard against moths, and avoid exposure to light. Use sponge-padded hangers, or store flat with as few folds as possible.

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Cocoons of silk

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Photos 7-9: Matsuida Machi, Annaka City, Gunma Prefecture, Japan; 10 and close-up pattern: Kiryu City, Gunma Prefecture, Japan