Marco Polo - Laurence Bergreen [92]
WHEREVER MARCO WENT, he encountered silk—and not just the fabric but the silkworms themselves, a great novelty to Europeans, and the mulberry trees on which they feasted. For centuries, Europe had known almost nothing about the art and science of sericulture; it was perhaps the most closely guarded secret in ancient history.
Even within China, the origin of silk was mysterious. Tradition credits Xi Ling-shi—a wife of the mythical Yellow Emperor, said to have ruled China in 3000 BC—with the introduction of silkworm cultivation and the invention of the loom. Although she was a phantom, silk was real; archeological digs have turned up silk threads, ribbons, and cocoons dating from 3000 BC, and a small ivory cup dating from 5000 BC contains images of spinning tools used for silk, as well as silk thread.
In China, a single cultivated species of moth became identified with silk, the blind and flightless Bombyx mori, whose ancestor Bombyx mandarina Moore fed on the leaves of the white mulberry tree. This silkworm’s thread is composed of a filament that is rounder and smoother than those produced by other moths, and across the millennia, thanks to persistent Chinese sericulture, it evolved into the more specialized Bombyx mori.
This moth lays as many as five hundred eggs, each weighing no more than a gram or so, within a few days’ time, and promptly dies. From that point, the story of silk can be told in a series of exploding numbers. An ounce of eggs eventually yields thirty thousand silkworms; the worms have one, and only one, source of food: the leaves of the mulberry tree. Those thirty thousand worms devour about a ton of mulberry leaves, and in turn produce twelve pounds of raw silk.
As the Chinese slowly perfected the cultivation of Bombyx mori, they learned to keep the eggs at 65 degrees Fahrenheit, and to raise the temperature 12 degrees to force them to hatch. Only then does the real work begin: feeding the worms fresh mulberry leaves, handpicked and carefully chopped, every half hour, around the clock, while maintaining a stable temperature. The worms quickly fatten in stacked trays stored in feeding huts; the sound of the munching creatures has been likened to heavy rain falling on a bamboo roof. At the same time, they must be protected from loud noises, drafts, and the odors of fish and meat and even perspiration; under ideal conditions, the coddled creatures can multiply their weight several thousand times, as they continually shed and change color.
To make their protective cocoons, the silkworms secrete a jellylike substance that hardens on contact with air. Over the course of three or four days, they spin a cocoon around themselves until they look like little puffy white balls about the size of a thumb. These are immersed in boiling water to loosen the silken filaments, which reach about half a mile in length, and the filaments, in turn, are gathered onto a spool.
There are two distinct types of silk cocoon. Cocoons of one type produce a filament about one-eighth the diameter of a human hair. The filament possesses tremendous tensile strength because of its molecular structure, known as a beta-pleated sheet, which looks like this:
A single silk thread generally consists of five to eight of these filaments tightly wound together. After processing, the raw threads are ready for dyeing. Because dye fits neatly into the pleats, silk retains color far better than other natural fabrics can; colors look much richer and more vibrant on the sensuous surface of silk.
The other type of silk cocoon, much larger and fluffier, often goes by the name of Happy Family, because each cocoon contains two larvae. The filaments in this case are tangled together, and so are less valuable. Once it has been stretched over a form to dry, the silk is used for batting—warm, lightweight