Silk

Silk (Anglo-Saxon, seole), a fibrous substance prepared from the cocoon of the silkworm, and used as the material of costly stuffs and garments. The name was derived through Latin, sericum, Greek, serikon, from ser, the Greek name of the silkworm, borrowed from the Chinese sze or si (in Corean sir). Seres, the name of the Chinese themselves, had the same origin.

The Silkworm. The silkworm is the larva or caterpillar of various moths belonging to the Bombycidae, Saturnidae, and other families of the order Lepidoptera. The most important is the Bombyx mori, a moth about an inch long (or in the case of the female somewhat larger), with dark wavy lines on its yellowish-white wings. It takes its name from the morus or mulberry-tree, the leaves of which form its principal food. The female lives but a short time after depositing her eogs on the leaves of the mulberry, and the males have also an ephemeral existence. The caterpillar, on emerging from the egg, is about 1/4 inch long, but before entering on the chrysalis stage at the end of six or eight weeks it attains the length of 3 inches. It is a hairless yellowish-grey insect, with a peculiar horn-like protuberance near its tail. During the larva stage it casts its skin four times. When the time for spinning approaches, it ceases to take any food. The gummy substance from which the silk is produced is secreted in two long glands which run along each side of the body, and end in a single opening on the lower lip, called the "spinneret" or "seripositor." Under the microscope the bave or thread of the cocoon is seen to consist of two filaments (brins) ejected from the two glands, which are supposed to adhere together in consequence of their own glutinous properties. The cocoon is of a white or golden-yellow colour, and about as large as a pigeon's egg. The spinning occupies about five days, and is followed by a period of pupa life lasting some two or three weeks. The Bombyx more produces but one generation aunually; in other cases two or more are produced, but the silk is then inferior.

Cultivation of the Silkworm. Success in sericulture depends in great measure on the leaves on which the worms are fed. It is important that the quality should be good and the supply abundant - conditions which are best secured in a high situation and on a dry soil. In Europe the Morus alba is generally preferred to other varieties. The eggs are now hatched by stove-heat, the temperature being gradually increased from 64° to 82° F. through a period of eight or ten days. Pieces of paper with small perforations are lald over the trays in which the hatching takes place, in order that the caterpillars may creep through the holes and thus rid themselves of portions of shell which might cause them death through constriction. It is important that the rearing-house should be roomy and well ventilated, and that overcrowding should be prevented, so as to allow each worm its due share of food and later on sufficient space in which to spin its cocoon. This is done in branches of brushwood or bundles of twigs placed for the purpose above the shelves or trays. If the silk is to be reeled, the moth must not be allowed to form within the shell and burst through the cocoon. The pupa is therefore killed by placing the cocoon in hot water or more usually in an oven heated by steam. The cocoons selected for breeding are laid on a cloth in a darkened room, the temperature of which ranges from 66° to 72° F. The sorter must be able to tell from the appearance of the cocoon whether the pupa is dead, and, if it lives, whether it will become a male or female moth, the sexes being distinguished by their difference in shape and size. Silkworms are liable to various diseases, the most important of which are Pebrine and Muscardine.

The Manufacture of Silk. Silk is either reeled or spun, the latter treatment being adopted only in the case of waste silk - i.e. damaged cocoons, the floss and husks of reeled cocoons, and the pieces of thread broken off in the processes of reeling and throwing, together with certain wild silks. Waste silk is spun into yarn in much the same manner as other fibres. The first step in the preparation of the better kind of silk is to place the cocoons in shallow basins of warm water, so as to soften the gum which holds the filaments together. The floss having been removed by means of a small brush made of twigs, the main filaments are caught, and, as they are unwound from their several cocoons, three or five are brought together so as to form a single strand, which is passed through an eyelet in the reeling machine. Care must be taken to preserve the thickness of the strand by supplying thread from a fresh cocoon when one of the former threads breaks or becomes exhausted.

The silk thus produced, called "raw silk," is made up into hanks. After the raw silk has been washed, it is subjected to a series of operations called "throwing," the purpose of which is to form it into stronger yarn. The hanks are first fixed on reels called "swifts," resembling those used in the former process, and as the swifts move the silk is wound on bobbins. The cleaning which follows is effected by passing the filament through a slit called the "cleaner," the silk being meanwhile reeled from one bobbin to another. This slit is the gauge of the thread, and presents an obstacle whenever there is any irregularity or coating of dirt. The silk is then passed over a smooth rod of metal or glass, and through a second guide to the bobbin on which it is wound. After this the thread is twisted so as to make it ready for doubling - i.e. removing the silk from several bobbins on to a single large bobbin, which is placed in the throwing machine. It is there wound by a ree1 into hanks, which are subsequently wound on reels and bobbins for the weaver. Raw silk may be either: (1) "singles," consisting of one strand of twisted silk composed of the filaments of eight to ten cocoons; (2) "tram," in which two or three strands are combined without being twisted before doubling; (3) "organzine," composed of two or sometimes three twisted strands which have been spun in the opposite direction to that in which each was twisted.

History of the Industry. For many centuries sericulture and the manufacture of silken goods were confined to China. According to a Chinese work entitled The Silkworm Classic, Se-ling-she, wife of the Emperor Hwang-te, herself reared silkworms and caused the mulberry-tree to be grown and silk to be reeled as far back as 2640 B.C. The industry made its way through Corea to Japan at the beginning of the 3rd century of our era, and a little later it became known in India, whence it spread to Persia and the regions of Central Asia. In the early days of the Roman Empire raw silk and silken goods were imported extensively from the East, but the worm was not reared nor looms set up before the time of Justinian. Subsequently the silk trade fell into the hands of the Arabs, who introduced it into all their settlements from Asia Minor to Sicily. After the fall of that people it continued to flourish in Apulia, and was also planted in Florence, Venice, Genoa, and Milan, which maintained their celebrity as silk-producing towns throughout the Middle Ages.

Silk-weaving and the rearing of silkworms were introduced into France in the reigns of Louis XI. and Francis I., but did not prosper greatly; the extraordinary progress of the industry in that country at a later date was due to the protective policy of Colbert. The English manufacture, which had been established in the 15th century, received a great stimulus from the immigration of Flemish weavers in 1585, and still more from the influx of skilled French artisans which followed the revocation of the Edict of Nantes. These mostly settled in Spitalfields, and the industry afterwards extended to Coventry, Derby, Macclesfield, Congleton, Leek, and other provincial towns.

Since the French treaty of 1860, which admitted French silks duty free, the English trade has greatly declined. France holds the foremost rank among silk-manufacturing countries, contributing between one-third and one-half of the textures produced throughout the world; to a large extent these are made from raw silk produced on French soil.