This section is from the book "School Needlework. A Course of Study in Sewing designed for use in Schools", by Olive C. Hapgood. Also available from Amazon: School Needlework: A Course Of Study In Sewing Designed For Use In Schools.
There is no more interesting subject than the source and manufacture of silk. The manufacture of silk doubtless originated in China. Although some silkworms are raised in this country, the greater part of the raw silk is imported from China and Europe.
The silkworm moth lays the eggs from which the silkworms are hatched, and they in turn become moths. The moth is about an inch long, having white wings marked with broad pale-brown bars. One moth lays from three hundred to seven hundred eggs, so small that it takes three or four hundred eggs to cover a space as large as a silver dollar. In a warm, dry temperature the eggs will hatch in a few clays. The young silkworm or caterpillar is dark-colored, and not more than a quarter of an inch in length. When full grown the worm is about three inches long; the body is made up of twelve joints, and it has sixteen legs. It reaches maturity in about a month, and during this time feeds upon the leaves of the mulberry tree, requiring constant feeding; it also changes its skin four times. When about to spin its cocoon on some convenient branch or roll of paper, it ceases to eat.
The silk is produced from two small bags filled with a liquid gum. From each bag comes a slender tube, which unites into one tube near the mouth, through which the gum is drawn and spun into silk; thus each fibre of silk, when examined under a microscope, is seen to consist of two strands, one from each bag. The silkworm first makes an outer covering of coarse fibres called floss-silk, then, bending itself like a horseshoe, and moving its head from one point to another, it entirely surrounds the body with silk, not spun regularly around the cocoon, but back and forth, so that sometimes yards may be unwound without turning over the cocoon. The inner silk is the finest. The cocoon is completed in a few days, and is about the size of a pigeon's egg. If left undisturbed, in two or three weeks the moth will eat its way through the cocoon, and in so doing break and injure the silk; to prevent this, it is stifled or killed by heat.
Each cocoon contains about one-fourth of a mile of thread, as fine as a cobweb, and it takes three thousand cocoons to make a pound of silk. The cocoons are first sorted, and. the outside threads removed. They are next placed in tepid water, where they are stirred until the ends of four or five threads are found and brought together into a single thread, which is wound on to a reel. Then it goes to the spinning-frames, where it is doubled and twisted into the various sizes required for sewing-silk or for weaving.
The silk after being cleaned (all the knots or obstructions removed) and dried, is ready to be colored and woven into fabric on the loom. Silk is the strongest of all fibres used for weaving.
The reeling or spinning of the silk is very difficult, as the cocoons differ in color, quality and length. The silk on the outside of the cocoon, and that near the chrysalis is inferior and broken; so this, with that from cocoons which have been injured, is made into what is called spun-silk. Raw silk is made from the perfect cocoons.