Silk, fiber produced as a cocoon covering by the silkworm, and valuable for its use in fine fabrics and textiles. The silkworm, in fact, is not a worm but a caterpillar. Although cocoon coverings of fiber are made by a large number of insects, only those of the mulberry silk moth, Bombyx mori, and a few other moths closely akin to it, are used by the silk industry. The silk of other insects, notably the spider, is used for certain manufacturing purposes, particularly for the cross hairs of telescopes and other optical instruments. For a description of the life and habits of the silk moth, see Silkworm.
Silk is one of the oldest known textile fibers and, according to Chinese tradition, was used as long ago as the 27th century bc. The silkworm moth was originally a native of China, and for about 30 centuries the gathering and weaving of silk was a secret process, known only to the Chinese. Tradition credits Hsi-ling-shi, the 14-year-old bride of the Emperor Huang Ti, with the discovery of the potential of the cocoon and the invention of the first silk reel. China successfully guarded the secret until ad300, when Japan, and later India, penetrated the secrecy.
References in the Old Testament indicate that silk was known in biblical times in western Asia, from which it was presumably transplanted to the Greek Islands of the Aegean Sea. The Chinese are believed to have built up a lucrative trade with the West from the days of the Han dynasty in the 2nd century bc. The ancient Persian courts used Chinese silks, unraveled and rewoven into Persian designs. When Darius III, king of Persia, surrendered to Alexander the Great, he was clothed in such silken splendor that Alexander was completely overshadowed and demanded as spoils the equivalent of $7 million in silk. Caravans carried silk on camelback from the heart of Asia to Damascus, Syria, the marketplace at which East and West met. Here silk was traded for Western luxuries, some of which survive in China today. Silk became a valuable commodity in both Greece and Rome. The Roman statesman and general Gaius Julius Caesar restricted silk to his exclusive use and to use for the purple Roman stripes on the togas of officials he favored. Despite this, however, the use of silk in Rome spread in the era of pomp and display.
Until ad550 all silk woven in Europe was derived from Asiatic sources. About that time, however, the Roman emperor Justinian I sent two Nestorian monks to China, where, at the risk of their lives, they stole mulberry seeds and silkworm eggs, secreted them in their walking staffs, and brought them to Byzantium. Thus, the Chinese and Persian silk monopolies ended. With the spread of Islam, the silkworm came to Sicily and Spain. By the 12th and 13th centuries Italy had become the silk center of the West, but by the 17th century France was challenging Italy's leadership, and the silk looms established in the Lyons area at that time are still famous today for the unique beauty of their weaving.
Not until after the revocation of the Edict of Nantes did Huguenot weavers from France cross the English Channel and establish silk mills in Spitalfields, a district in the East End of London. The silkworm, however, did not flourish in the English climate, nor has it ever flourished in the United States. The first silk mill in the U.S. was erected in 1810. With the advent of the power loom and with the help of the high tariffs, introduced during the American Civil War, against imported woven goods, the American silk-weaving industry entered a period of growth. Only in China, Japan, and, to a lesser extent, Italy and France was the silk itself produced, however.
In addition to the true silk from the cultivated mulberry silkworm, a number of so-called wild silks are produced from other related species of insects in the uncultivated state. Tussah silk, for example, is produced from a species that feeds on oak leaves. Douppioni is a silk produced from two silkworms that spin a cocoon together and thus produce a double thread. Special types of weaves, such as shantung and other irregular types, are woven from these types of silk.
The advent of synthetic fibers such as nylon and polyester, which are stronger than silk and lower in price, but do not possess the same hand, or quality, has caused a tremendous reduction in silk production and consumption. World production in 1940 was 59 million kg (130 million lb). By 1950 it had dropped to 19 million kg (42 million lb), but by the mid-1980s had climbed to about 68 million kg (150 million lb).
In the U.S., silk is still used for clothing, including lightweight suits, coats and slacks, jackets, shirts and neckties, robes, loungewear, underwear, hosiery, and gloves. Silk is also used in lace, napery, draperies, linings, narrow fabrics, and handbags.
Sericulture, or the raising of silkworms, involves the incubation of the tiny eggs of the silkworm moth until they hatch and become worms. After hatching, the worms are placed under a layer of gauze, on which is spread a layer of finely chopped mulberry leaves. For six weeks, the worms eat almost continuously. At the end of this period, they are ready to spin their cocoons, and branches of trees or shrubs are placed in their rearing houses. The worms climb these branches and make their cocoons in one continuous thread, taking about eight days for the process. The amount of usable silk in each cocoon is small, and about 5500 silkworms are required to produce 1 kg (2.2 lb) of raw silk.
After the complete cocoons have been gathered, the initial step in silk manufacture is to kill the insects inside them. Thus, the cocoons are first boiled or treated in ovens, killing the insects by heat. The silk fiber is obtained from the cocoons by a delicate process known as reeling, or filature. The cocoons are first heated in boiling water to dissolve the gummy substance that holds the cocoon filament in place. After this heating, the filaments from four to eight cocoons are joined and twisted and are then combined with a number of other similarly twisted filaments to make a thread that is wound on a reel. When each cocoon is unwound, it is replaced with another cocoon. The resulting thread, called raw silk, consists usually of 48 individual silk fibers. The thread is continuous and, unlike the threads spun from other natural fibers such as cotton and wool, is made up of extremely long fibers. Along with cocoons damaged by emerging worms used for breeding stock, the filaments from the coarse outer portion of the cocoon, which is removed by brushing before reeling, and the inner portion of the cocoon, which remains after reeling the raw silk, are mixed to produce a low grade of silk staple that is spun into yarn.
The next step in the processing of silk is the twisting of one or more threads of the raw silk into a strand sufficiently strong for weaving or knitting. This procedure is called throwing. Four different types of silk thread may thus be produced: organzine, crepe, tram, and thrown singles. Organzine is a thread made by giving the raw-silk thread a preliminary twist in one direction and then twisting two of these threads together in the opposite direction at the rate of about 4 turns/cm (10 turns/in). Crepe is similar to organzine but is twisted to a much greater extent, usually between 16 and 32 turns/cm (40 and 80 turns/in). Tram is made by twisting in only one direction two or more raw-silk threads, with 8 to 12 turns/cm (20 to 30 turns/in). Thrown singles are individual raw-silk threads that are twisted in only one direction, the number of turns depending on the quality of thread desired. In general, organzine thread is used for the warp threads of materials, and tram threads for the weft, or filling. Crepe thread is employed in the weaving of characteristic crinkly fabrics, and single thread is used for sheer fabrics.
Microsoft ® Encarta ® Encyclopedia 2005 ©