Sericulture:The Silkworm and Silk-making Process
Posted by: Leo in Other-Agri 1,730 Views
Silk is undisputedly the most beautiful of all natural fibers, with its unearthly sheen. It is also uncommonly strong, even at its finest, when it is almost invisible. It is unlike any other fiber used to make fabrics, for it is neither grown in a field or on an animal. It is not manufactured in a factory. A humble caterpillar about the size of a woman’s smallest finger produces the silk fiber, spinning it out of its mouth, using tiny fore-legs to place the silk where it should go. It is known scientifically as Bombyx mori, although other species of silkworm produce less famous types of silk
The process of making silk has not changed very much in the thousands of years since the silkworm’s thread was first used, in ancient China. Wooden trays may be exchanged for the more sanitary plastic ones. Powdered silkworm chow is available for those without access to fresh mulberry leaves, making it possible for more people to grow silkworms, and at times of year when the mulberry leaves are not around. Over the centuries, the silkworm moth has lost its ability to fly, but that has little bearing on its care or cultivation. It is still a hands-on process involving live creatures, and takes a lot of time. But the result is certainly worth all the work and will certainly give one a truer understanding of why silk has been so desirable and so expensive throughout history.
The silkworm isn’t really a worm,… it’s a caterpillar! The silkworm has been used by people for over 4,000 years to make silk. The practice first began in China in about 2600 BC. The Chinese kept the secret of producing silk for thousands of years, trading silk to Europe and the Middle East. But eventually the secret of how to get silk from the silkworm was learned by other countries. More recently we have learned how to make silk-like material from synthetic materials, but the demand for real silk is still high, and silkworms are still raised for the silk threads they produce.
The practice of raising silkworms is called sericulture.
The silkworm, when fully grown, reaches a length of about 5 to 7 centimeters, and it’s an amazing worker. In only a few days, a single silkworm spins a cocoon from which can be removed a silk thread up to 600 meters in length. But it still takes about 25,000 cocoons to make half a kilogram of raw silk. Most of the silk today is produced by China and India, and a few other countries. 60,000 tonnes of raw silk are made each year, and are turned into dresses, shirts, bed sheets, curtains, and other products. It’s a big industry, especially in China, where ten million Chinese farmers grow silkworms, and another half million make silk fabrics. There are 600 silk weaving mills in China.
Silkworms, offspring of moths, produce their highly-desirable, pricey silk, by spewing out thread from tiny holes in their jaws, which they use to spin into their egg-bearing cocoons. This entire production takes a mere 72 hours, during which time they produce between 500-1200 silken threads. These miniature, mulberry leaf-munching marvels lay, at minimum, 500 eggs each spring, thereby increasing the number of workers for the production line.
A silkworm moth is yellowish-white, with a thick, hairy body, and a wingspread of about 4 cm. The adults live only a short time… long enough for the female to lay her eggs. The larvae, which hatch in about ten days, are about half a centimeter long. Larvae in captivity are fed their favorite food, the leaves of the white mulberry plant, so they will produce the finest quality silk. Full-grown larvae are up to 7 cm long, and yellowish-gray in color.
After about six weeks of continuous eating, the larvae climb to the top of a branch and spin their cocoon. It takes about six days, and to do it they produce one continuous long silk thread. They will emerge from their cocoon after several weeks of pupating, as adult moths. But on silkworm farms, only enough adult moths are allowed to emerge to ensure continuation of the species, since they destroy the cocoon when emerging. The remaining silkworms are killed by heat while they are inside their cocoons, so that the silk can be drawn off and spun into threads, and woven into fabric
The ancient Chinese unearthed the silkworm’s secret, and were the first to spin the silkworm’s threads into cloth. They kept this covert, top-secret operation, from the rest of the world by imposing the death sentence upon those who smuggled the worm and/or its eggs out of China. Eventually, however, the secret was out, and silkworms are now farmed for their silk, in China, of course, in Japan, in India, in France, in Spain, and in Italy. These countries harness the power of the silkworm through a tedious, labor-intensive, time-consuming process, a process which prominently figures into the price of silk.
Farm workers painstakingly place the 500 plus eggs the prized grayish-white moth lays, upon strips of paper or cloth (not made of silk!), until the following spring, when the incubated eggs hatch, and the tiny, black worms emerge. Once hatched, workers transport the worms to trays brimming with the worm’s favorite fodder of finely chopped, white mulberry leaves. After approximately 6 weeks, the satiated worms begin slowly to sway their heads back and forth to signal that show time is at hand.
Once the silkworm completes its cocoon, the farmer snatches his cocoon from him, to prevent the shrunken chrysalis, carefully encased inside, from hatching into a moth in 12 days. The silk farmers ensure that this event does not transpire, and does not kill his moneymaking venture, by exposing the cocoons to heat, thereby executing the chrysalis. Now, the silkworm’s labor of love is prepared for the silk production process.
The process begins by bathing the now-empty cocoons in troughs of warm water, which serves to soften the gum binding the silken filaments together. He now proceeds with the arduous task of unraveling several cocoons, and winding the filaments onto a reel that twists 10-12 filaments together into a “single” thread of silk. The end product is a skein of raw silk, which the farmer profits from by selling to the highest bidder.
Around the world there are different varieties of silkworm used to make different types of silk; there is even one type of silkworm that makes a cocoon together with another silkworm, producing a double-thread! Although synthetic fibers such as nylon and polyester, which are stronger than silk and lower in price, have turned silk into a luxury product, silk is still in demand because of its superior look and feel.
The Process
Producing silk was a lengthy, complex process. As show in the illustrations below, men took responsibility for the mulberry trees, growing the only food silkworms eat, but women were responsible for the critical task of feeding the leaves to the silkworms. Silkworms do not spin cocoons on demand; timing and temperature have to be handled carefully, and during the month between hatching and spinning the cocoons have to be fed every few hours, day or night. If properly coddled, the worms eventually spin cocoons for several days, each cocoon made up of a strand of silk several thousand feet long. Over two thousand silkworms are needed to produce one pound of silk.
- The sericulture process begins with washing the silkworm eggs that had been stored over the winter.
- After the eggs have hatched, the larvae are spread out on trays to grow. They are fed chopped mulberry leaves for about a month.
- During the final few days before the worms spin their cocoons, the worms may need to eat ten times a day.
- The rushes on the trays have to be cleaned regularly.
- Prepare the frames for the silkworm mats, where the worms will be placed for spinning.
- Spinning may take about a week, after which the cocoons have to be unraveled. Here the cocoons are in a pot of hot water, which both kills the worms and loosens the filaments and lets the cocoons float freely. The filaments from several cocoons are reeled off together to make a strong thread.
- To make stronger warp threads, it is necessary to twist several single threads together on a spooling frame.
- Silk threads are wound onto smaller reels for weaving. In preparation for weaving, the warp threads are laid out and rolled up.
Some silk-making illustrations here
sources: coolquiz.com, worsleyschool.net, chateau-michel.org, depts.washington.edu
For more information, contact:
Dept. of Science and Technology
Rm. 303 DOST Bldg., DOST Complex,
Gen. Santos Ave., Bicutan, Taguig City 1631
Telephone Nos: (632) 837-20-71 to 82
Fax: (632) 837-8937
Web: www.dost.gov.ph
Dept.of Agriculture
D.A. Compound, Elliptical Rd.,
Diliman,Quezon City
Tel. Nos. (632) 929-6065 to 67 / 920-3991 / 928-1134
Web: www.da.gov.ph
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