silk

Introduction

silk, fine, horny, translucent, yellowish fiber produced by the silkworm in making its cocoon and covered with sericin, a protein. Many varieties of silk-spinning worms and insects are known, but the silkworm of commerce is the larva of the Bombyx mori, or mulberry silkworm, and other closely related moths. Wild silk is the product of the tussah worm of India and China, which feeds on oaks. It is now semicultivated, as groves of dwarf trees are provided for its feeding. It spins a coarser, flatter, yellower filament than the Bombyx mori, and the color does not boil out with the gum. Tussah silk is a rough, durable, washable fabric known as shantung or pongee.

History

Sericulture (the culture of the silkworm) and the weaving of silk have been practiced in China from a remote period. Legend dates this back to 2640 b.c., to Empress Si Ling-chi, who not only encouraged the culture of the silkworm but also developed the process of reeling from the cocoon. This was a closely guarded secret for some 3,000 years. Silk seems to have been woven very early on the island of Kós, which Aristotle mentions, in a vague description of the silkworm, as the place where silk was “first spun,” In the 1st and 2d cent. a.d. silk fabrics imported to Greece and Rome were sold for fabulous prices.

Up to the 6th cent. raw silk was brought from China, but death was the penalty for exporting silkworm eggs. About a.d. 550 two former missionaries to China, incited by Emperor Justinian, succeeded (says Procopius) in smuggling to Constantinople, in a hollow staff, both the eggs of the silkworm and the seeds of the mulberry tree. Byzantium became famous for splendid silken textiles and embroideries, used throughout medieval Europe for royal and ecclesiastical costumes and furnishings. In the 8th cent. the Moors began to carry the arts of silk culture and weaving across the northern coast of Africa and to Spain and Sicily, and in the 12th cent. Spain and Sicily were weaving silks of exquisite texture and design.

Other areas of Europe subsequently became great weaving centers. Lucca, in N Italy, had established looms by the 13th cent., and in the 14th cent. the city became famous for its materials and designs. Florence and Venice followed and wove sumptuous fabrics and velvets enriched with gold thread. Genoa's velvets became well known. France established looms, and under Louis XIV's minister Jean Baptiste Colbert it set the fashion with its beautiful silks. Lyons in S France became an important weaving center. Early attempts were made in England under Henry VI to establish the silk industry, but it was not until the revocation of the Edict of Nantes, when many French refugee weavers fled to England, that the industry received a real impetus. The French settled in Canterbury, Norwich, and other places; but it was in Spitalfields, London, that the industry became important.

Many attempts were made to establish sericulture in the American colonies: inducements such as land grants and bounties were offered, and many mulberry trees were planted. In 1759 Georgia sold more than 10,000 lb (4,535 kg) of cocoons in London. Pennsylvania had a silk industry, fostered by Benjamin Franklin, until the Revolution. The high cost of labor seems to have been the main deterrent to the success of sericulture in America.

Types of Fabrics

Fabrics made are plain weaves (taffeta, pongee), cords (faille, poplin), gauzes (net malines), pile fabrics (plush, velvet), crepes, satins, damask, ribbons, and brocade. Some of these weaves are ancient, developed on the shuttle looms of China and the handlooms of India, Greece, and Europe. In Europe and Asia the handloom is still used for the finest fabrics. Japan and China lead in the production of raw silk, with India, Italy, and France following. The United States is the largest importer.

Silk Manufacturing

In silk manufacture, the first operation is reeling. The cocoons, having been sorted for color and texture, are steamed or placed in warm water to soften the natural gum. They are then unwound; each cocoon may give from 2,000 to 3,000 ft (610–915 m) of filament, from 4 to 18 strands of which are reeled or twisted together to make an even thread strong enough to handle. This is called raw silk. Formerly a hand process, this work is now done in Europe and in some parts of the Orient in factories on simple machines called filatures.

The next step, called throwing, is preparing the raw silk for the loom by twisting and doubling it to the required strength and thickness. This process also is now mostly done in large mills with specialized machinery. Silk, after throwing, has three forms—singles, which are untwisted, used for the warp of very delicate fabrics; tram, two or more singles, twisted and doubled, used for the weft of various fabrics; and organzine, made of singles twisted one way, then doubled and twisted in the opposite direction, used for the warp of heavy fabrics. For sewing and embroidery thread, more doubles and smoother twists are made. In modern factories spinning frames complete the preparation for the loom.

The silk is boiled off in soapsuds to remove gum and prepare it for dyeing. For white and pale tints it must be bleached. Scouring or boiling causes loss of weight, sometimes made up by loading with metallic salts, as tin, which has an affinity for silk and can be absorbed to excess, causing weakening of the fiber. Dyeing may be done in the yarn or in the piece. Finishing processes are varying and important, as in making moires. Weaving is done as with other textiles, but on more delicate and specialized looms.

Bibliography

See L. Boulnois, The Silk Road (tr. 1966).

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