Fibre to Fabric
Science Class Seven
Silk: Discovery and cocoon to silk
The Silk fibre is obtained from Silk Worm. Since, silk worm is an animal, so fibre, i.e. silk obtained from it is called animal fibre.
Silk fibre is used to make yarn. Silk fibre is like human hair or wool which are also made of natural protein.
Silk is obtained from the cocoons made by silkworm. Most of the fabrics made of silk can be hand washed. Silk does not shrink like other fabrics. Fabrics made of silk is credited high quality. Silk sarees and other dress materials are famous all over the world.
Sericulture
The rearing of silkworm is known as Sericulture. Sericulture is done mainly in order to obtain silk fibre.
History of Discovery of Silk
There is an old Chinese legend story behind the discovery of silk.
Once upon a time, there was a king named Huang-ti. He had been noticing for a long time that in his garden the leaves of mulberry were getting damaged continuously. He told the queen Si-lung-Chi to probe into it and try to find the cause.
After a long observation the queen found that there were many white worms eating up mulberry leaves continuously. She also noticed that those white worms were spinning shiny cocoons around them.
Once when she was taking tea sitting under a mulberry tree, a cocoon dropped into her cup of tea. After getting the heat from a tangle of delicate threads started separating out from the cocoon which was dropped in her cup of tea. This was silk.
By this way, silk fibre was discovered accidently like many other discoveries.
The actual date of discovery of silk is still unknown, but it is said that Silk was first discovered in China around 5000 to 8000 years ago. After discovery of silk, China started producing silk. But, Chinese kept it a secret for hundreds of years.
Silk Trade & Silk Route
Later on, around 2000 BC silk was introduced to other countries by travelers and traders.
The trade of Silk was so extensive that the major set of trade routes between Europe and Asia developed. The route which was used by traders is still known as the Silk Route or Silk Road. The trade of silk started and got at its high level in the reign of Han dynasty in China around 207 BCE to 220 CE.
UNESCO in June 2014 declared the Chang'an-Tianshan corridor of the Silk Road as a World Heritage Site.
Silkworms feed on fresh mulberry leaves, and for a long time mulberry trees only grew in China and Japan (and East Asia generally), so silk is brought from East Asia to the rest of the world.
Life Cycle of silk moth
* The female silk moth lays eggs.
* These eggs hatch into larva. These larva are called caterpillars. Caterpillars are fed mulberry leaves continuously.
* After feeding mulberry leaves for about 25 days, caterpillars become ready to spin the silk cocoon.
* Caterpillars make cocoon for themselves to develop them into silk moth. In this stage caterpillar is called pupa. In the cocoon it moves its head side to side in a way of making the figure of eight (8). During this movement, pupa produces the liquid protein by secreting from its two glands present in its head.
* The liquid so produced by pupa when comes in contact with air, it gets solidified, this is called the silk fiber.
* The pupa (silkworm) spins approximately 1 mile of filament and completely encloses itself in a cocoon. This process takes about two or three days.
From Cocoon to Silk
Silk months are reared to obtain cocoons. Cocoons are either put under sun or boiled in hot water to separate out silk threads.
Rearing of Silk worm (Cultivation of silk) : Sericulture
Female Silk Moths lay eggs on specially prepared paper. Generally one silk moth lays 300 to 500 eggs at a time. These eggs are kept under suitable temperature, humidity, and hygienic conditions.
After hatching of eggs, the caterpillars are kept generally in the tray made of bamboo and are fed fresh mulberry leaves.
A straw or bamboo frame is placed over the tray of caterpillars. Caterpillars continuously feed mulberry leaves. About after 35 days caterpillars stop eating and begin spinning cocoons by moving its head in the pattern of "figure of 8".
Two glands which are located near the head of caterpillars, produce liquid silk, a type of protein. The opening present in the head of caterpillars through which liquid silk is produced to spin cocoons are called spinnerets. Liquid silk gets coated with sericin which is a water-soluble protective gum. This solidifies when come in contact with air.
Within 2 to 3 days, one caterpillar spins about 1 mile of filament. In this process caterpillar is completely encased itself into a cocoon. In cocoons caterpillars develop into the silk moth.
From these cocoons, which are made by pupa, silk threads is obtained.
Amount of usable silk in each cocoon is small. About 3000 to 5500 silkworms are required to produce 1 kg of silk. The silk is obtained from the undamaged cocoons by brushing the cocoon to find the outside end of the filament.
The silk fibre obtained from the cocoon is known as raw silk.
Separating out the silk from cocoon: Reeling of Silk
The farmers leave some cocoon having silkworm to breed the next generation of caterpillar.
Harvested cocoons are soaked in boiling water. This soften the sericin holding the silk fibers together in the cocoon shape. The fibers are then unwound to produce a continuous thread.
The process of taking out threads from the cocoon for use as silk is called reeling the silk. Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon. After unwinding, silk fibres are spun into silk threads.
Silk fabrics are made using silk thread by the process of weaving. Weaving of silk fabric is done in factories. Before invention of weaving machine, weaving was done using handlooms by weavers. Even today at some places weaving is done manually.
Types of Silk
The type of silk depends upon the types of silk moth. There are many varieties of silk moths. Different silk month produces different texture and variety of silk.
Bombyx Mori is the most common silk moth. It is also known as mulberry silk moth because it only feed on mulberry leaves.
Tassar silk, Mooga or Muga silk, Kosa silk, Eri silk, etc. are some of the varieties of silk.
The silk fibre obtained from the cocoon of mulberry silk moth is soft, lustrous and elastic. Silk can be dyed in different beautiful colours.
Use of Silk
Silk fabrics are used in making garments, Sari, and other type of fancy cloth.
Sericulture or culture of silkworms is a very old occupation in India. India is the second largest producer of silk. Proof of making of silk is found from the remains of Indus Valley Civilization.
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