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Silky Secrets

An ancient mystery hits the road.

Courtesy American Museum of Natural History.
Courtesy American Museum of Natural History.

About 2,000 years ago, traders dazzled ancient Romans with a shimmering cloth from faraway lands in the East. The material was strong but soft. It kept wearers cool in hot weather and warm in cold weather. Romans had never
seen anything like it — and they were hooked.

Traders charged high prices for the fabric and brought riches back east. What was this miracle material that had ancient Romans dishing out their gold? Silk! But when the Romans tried to make this treasure for themselves, they were stumped. They knew of other cloths, such as linen and cotton,  that were made from plants. So they mistakenly guessed that silk came from a plant. Why was silk-making such a mystery?

Mystery Material

Romans didn’t know the people who made silk. The glistening material came from China over a network of trading pathways called the Silk Road. The route stretched from Asia through the Middle East and into Europe. But merchants didn’t make the whole trip themselves. “People would take their goods a couple hundred miles, they’d trade it for other things, and then they’d go back in the other direction,” explains Mark Norell, curator of Traveling the Silk Road, an exhibition at the American Museum of Natural History in New York City. Merchants at one end of the Silk Road could only guess what happened at the other end.

Since China’s rulers were making a fortune on the silk trade, they forbade their people to teach sericulture to others. “It was a penalty of death if you shared silk-making secrets with foreigners,” Norell says.

When Romans looked to plants for the answer, they were barking up the wrong tree. Far away, tiny animals were spinning the mysterious material.

Spinning a Secret

At least 5,000 years ago, the Chinese discovered the secret—that caterpillars spin cocoons of silky filaments. The practice of silk farming was born.

Silk farmers cared for a type of insect called the domestic silk moth. Each female moth would lay up to 500 pinpoint-size eggs before she died.

Silk farmers placed the eggs in shaded trays. Ten to 12 days later, the larvae, in the form of tiny caterpillars, crawled out. Because these caterpillars, known as silkworms, are picky eaters, their caretakers served up their favorite food—mulberry leaves. The caterpillars molted, or shed their skin, as they grew. Their weight multiplied 10,000 times in one month!

After several molts, farmers set up frames of twigs. Each caterpillar climbed a twig and produced a silky filament from glands in its head. The caterpillar spent days wrapping itself in this filament, which hardened as it was exposed to air. The result: a white, puffy cocoon made of pure silk.

Unwrapped

Normally, the pupae inside the cocoons would transform into moths. But silk farmers couldn’t let this happen. “If it changes into a moth, the threads are broken as the animal climbs out,” Norell says. So the farmers baked or steamed the cocoons and soaked them in salt water to kill the pupae. Then they dumped the cocoons in boiling water to loosen the filament. Each cocoon unraveled into a single silken strand 600 to 900 meters (1,970 to 2,950 feet) long. That’s twice the height of the Empire State Building!

But the strands were so fine that workers had to wind several filaments together to make one silk thread. One silk robe, for example, required 2,500 cocoons.

The Secret’s Out

The Chinese couldn’t keep the secret of silk-making forever, and over time, sericulture spread to other lands. According to one legend, in 522 A.D., two monks hid silk moth eggs inside their walking sticks and smuggled them to Europe.

But the finest silk still came from China. The Silk Road reached its peak during China’s Tang Dynasty (618 to 906 A.D.). Traders used this network not only for silk but also other goods, technologies, and ideas. “Just about everything that could be traded was traded,” Norell says.

After thousands of years, the steps for making silk haven’t changed, although machines now do some of the work. When you wear a silk shirt, sleep with silk sheets, or use a silk-lined sleeping bag, you’re benefiting from an ancient discovery that’s still popular.

Check It Out

Experience thousand-year-old adventures by Traveling the Silk Road: Ancient Pathway to the Modern World. This new exhibition from the American Museum of Natural History opens November 14, 2009, and features several life-size models of camels. These animals were knows as “boats of the desert.”

Camels sweat very little but can lose up to 30 percent of their weight in water . . . and can then slurp it all back in less than 15 minutes. Learn more about camels and ancient trade routes by asking your teacher or by visiting www.amnh.org.

Words to Know

Sericulture—The practice of silk production.

Filament—A fine thread.

Larvae—Insects in an immature stage of development.

Molt—To shed the skin.

Gland—An organ that produces and secretes chemicals.Pupae—Insects in the transformation stage between larvae and adults.

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