Silk. The silk of commerce is obtained from the cocoons of several species of insects. These insects resemble strongly the ordinary caterpillars. At a certain period of its existence the silkworm gives off a secretion of jelly-like substance. This hardens on exposure to the air as the worm forces it out and winds it about its body.
MOTH, SILKWORM, AND COCOONS
It takes about three days for the worm to form the cocoon. After the cocoon has been formed the silkworm passes from the form of a caterpillar into a moth which cuts an opening through the cocoon and flies away. It is very important that the moth should not be allowed to escape from the cocoon; the mere breaking of the cocoon greatly decreases the value of the thread. The cocoon is preserved by killing the chrysalis by heat.
There are a great many varieties of caterpillars, but few of them secrete a sufficient quantity of silk to render them of commercial value. The principal species is the mulberry silkworm which produces most of the silk in commerce. It is cultivated and fed on mulberry leaves. There are other varieties of silkworms that are not capable of being cultivated and are called wild silkworms. The silk produced by the wild worms of China and India is called “tussah” (or “tussur”). The silk is inferior to that produced by the cultivated worms and is used for making pile fabrics, such as velvet, plush, etc.
The color of the cocoons varies greatly. Most of the European cocoons are bright yellow, though some are white. The Eastern cocoons, on the other hand, are mostly white, while a few are yellow. The wild silks are for the most part écru color, though some are pale green. The color, except in the wild silks, is derived from the gum which is secreted by the worm, and with which the fibers are stuck together. This gum comprises from 15 to 30 per cent of the weight and is removed by boiling in soap and water before the silk is dyed. All silks except the wild silks, after the gum is removed, are from white to cream in color. The tussah, or wild silks, remain an écru color.
REELING RAW SILK
The greatest care has to be exercised throughout in the care of the moths, eggs, worms, and cocoons—this being the succession of changes. That is, the moth lays eggs which are collected and kept cool till the proper season for incubation. They are then kept warm during the time occupied in hatching, sometimes about the person of the raiser. After a time these eggs hatch out worms, tiny things hardly larger than the head of a pin. After the worms are hatched they require constant care and feeding with chopped mulberry leaves till they reach maturity. They are then about three inches in length, and spin their cocoons from a fiber and gum which they secrete. When the cocoons are spun the worms become chrysalises inside of them. The cocoons are then collected and the chrysalises killed, generally by heat, before they can again become moths.
Raw Silk. The cocoons are next sent to the reelers or filatures. A number of cocoons, greater or less, according to the size of thread desired, are placed in a basin of hot water, which softens the gum. After the outside fibers are removed so that the ends run free, the ends are collected through a guide and are wound upon a reel. As the silk cools and dries, the gum hardens, sticking the fibers from the different cocoons together in one smooth thread varying in size according to the number of cocoons used. After the silk has been reeled and dried it is twisted into hanks and sent to America and other countries as raw silk.