In countries like India and China, silkworms continuously reproduce round the year. Also, the silkworms are made to reproduce throughout the year when bred for various commercial purposes. These insects have to be bred very systematically for commercial purposes. They cannot feed on their own, they have to be fed. Thus, everything from their food to their habitat is organized artificially in order to make them breed and survive. As we know that silkworms feed on mulberry leaves, it is not always possible to find them, especially during fall and winter. Hence, the commercial breeders feed these little moth with a substance called silkworm chow, which is a good substitute for mulberry leaves.
The commercial process of converting a silk fiber into a fabric is highly complex and labor intensive. The following are the steps on how the silk fibers get woven into the fabric that we sell at Brave Era:
- Hatching of the eggs
- The feeding period
- Spinning the cocoon
- Silk Reeling
Sericulture is basically the production of silk and the rearing or cultivation of the silkworm for this purpose. Although various insects produce silk of different quality, only the filament produced by Bombyx mori, the mulberry silk moth and a few others in the same genus, is widely used by the commercial silk industry.
Hatching of the Eggs
The initial stage of silk production is the laying of silkworm eggs, in a controlled habitat such as an aluminum box, which is then carefully inspected to ensure they are free from diseases. The female deposits about 300 to 400 eggs at a time.
The male moth dies within 24 hours while the female silk moth dies eventually after depositing the eggs. The adult moth possesses rudimentary mouthparts and does not eat during the short period of their lifetime.
The tiny eggs of the silkworm moth are incubated for 10 days approximately until they hatch into larvae or caterpillars. At this point, the larva grows into a quarter of an inch long.
The Feeding Period
After hatching from the eggs, the larvae are fed huge amounts of chopped mulberry leaves and are placed under a fine layer of gauze. Meanwhile, they shed their skin four times. The larvae may also feed on Osage orange or lettuce. However, larvae fed on mulberry leaves produce the very finest silk fibres. Did you know a larva can eat 50,000 times its initial weight in plant material? The silkworm feeds almost continually for about six weeks. After growing to its maximum size of about 3 inches at around 6 weeks, it stops eating, changes color, and is about 10,000 times heavier than when it hatched.
The silkworm is now ready to be spun as a silk cocoon.
Spinning the Cocoon
The silkworm attaches itself to a compartmented frame, twig, tree or shrub in a rearing house to spin a silk cocoon over a 3 to 8 day period. This period is termed as pupating.
Silkworms have a pair of specially modified salivary glands known as sericteries, which are used for the production of fibroin, a clear, viscous, proteinaceous fluid that is forced through openings called spinnerets on the mouthpart of the larva.
Liquid secretions from the two large glands in the insect emerge from the spinneret, a single exit tube in the head. The thickness of the silk thread is determined by the diameter of the spinneret, which is produced as a long, continuous filament. The secretions harden on exposure to the air and form twin filaments composed of fibroin, a protein material. The second pair of glands secretes a gummy binding fluid called sericin which bonds the two filaments together.
Steadily over the next four days, the silkworm rotates its body in a figure-8 movement some 300,000 times, constructing a cocoon and producing about a kilometer of silk filament.
Silk reeling is the process by which a number of cocoon baves are reeled together to produce a single thread. This is the last technique that is primarily implemented in modern silk reeling processes. This is achieved by softening the sericin and then delicately and carefully unwinding filaments collectively from a group of cooked cocoons at one end in a warm water bath and winding the resultant thread onto a fast moving reel.
As the sericin protects the silk fiber during processing, this is often left in until the yarn or even woven fabric stage. Raw silk is silk that still contains sericin. Once this is washed out in soap and boiling water, the fabric is left soft, lustrous, and up to 30% lighter. The amount of usable silk in each cocoon is small, and about 2500 silkworms are needed to produce a pound of raw silk.
Types of Silk
Throwing is a process of creating the silk yarn by twisting the raw silk is twisted into a strand which is strong enough for weaving or knitting. Throwing prevents the thread from splitting into its integrant fibers.
There are basically four different types of silk thread that may be produced from this procedure:
- Thrown singles, and
- Crepe is produced by twisting individual threads of raw silk by doubling two or more of these together and then twisting them again.
- Tram is made by twisting two or more threads in only one direction.
- Thrown singles are single threads that are twisted in only one direction.
- Organzine is made by giving the raw silk an initial twist in one direction and then twisting two of these threads together in the opposite direction.
Generally, an organzine thread is used for the warp threads of materials, tram threads for the weft or filling, crepe thread for weaving crinkly fabrics and a single thread for sheer fabrics.
The broken or waste filaments and damaged cocoons are retained, treated to remove the sericin, and combed. This is then processed into yarn and is marketed as spun silk, which is of inferior quality and is much cheaper compared to the reeled product.