From Cocoon to Silk: History, Properties, Processing, Uses

Silk is an animal fibre obtained from the cocoons of silkworms. A large number of these cocoons are unwound carefully to make long threads. These threads are spun together to make them thicker and then woven to make silk. Raising silkworms for the production of raw silk is known as sericulture. In this article, we will learn about the process of conversion from Cocoon to Silk. Read on to learn more.

History of Silk

Silk is a valuable fabric that symbolises wealth and prosperity. In earlier times, the use of silk was reserved only for kings and monarchs. The Romans sold silk for its weight in gold. The Chinese have been using silk since the \({27^{{\rm{th}}}}\) century \({\rm{BC}}\). China is credited with the first production of silk at around \(3000\, {\rm{ BC}}\). For more than \(30\) centuries, the Chinese recognised the significance of the magnificent substance they were manufacturing and kept it a secret from the rest of the world.

Introduction to Silk

Silk is a strong but light and soft cloth having a shimmering appearance. The silk fibres are also animal fibres obtained from the cocoons of silk moths (silkworm). The silk fibre is formed of two proteins, i.e., sericin and fibroin. These proteins make the fibre shiny and lustrous. The rearing of silk moths for obtaining silk is called sericulture.

Study Life History of Silk Moth Here

Properties of Silk

1. Texture: It is soft, smooth and lustrous.
2. Strength: It is the strongest natural fibre.
3. Absorption of moisture: The absorptive capacity of the silk fabric makes comfortable apparel even for a warmer atmosphere.
4. Insulating nature: It is cool to wear in the summer and warm to use in the winter.
5. Cleanliness and Washability: Silk fabric does not attract dirt because of its smooth surface.
6. It is a bad conductor of heat.
7. It is very elastic, thus resists creasing.
8. It is resistant to dust.
9. It has a peculiar natural shine and dyes well.

What is Sericulture?

Silk is obtained from the cocoons of silkworms. These cocoons are unwound to make long threads. These are then spun together to make thicker and then woven to make silk. The steps involved in the sericulture process are:

1. For the production of silk, the healthiest moths are chosen for breeding and laying eggs. The eggs that have been stored are then washed, which hatch only once a year in Spring.
2. The lava that emerges out from the eggs is spread out on trays to grow. They are fed with mulberry leaves for about \(25\) to \(35\) days.
3. When the silkworm is about \(35\) days old, it starts spinning a cocoon around itself. This takes about three to seven days to complete.

Processing of Silk Fibre from Silk Cocoon

Once the complete cocoons are formed, they are gathered. The initial step in the harvesting of silk fibre is to kill the insect inside the cocoon. For killing, the cocoons are boiled in water. The boiling hot water not only kills the insects within the cocoon but dissolves a gummy substance that holds the cocoon filament in place. The cocoons are then dried and brushed to remove the coarse outer portion, which consists of coarse filaments.

After brushing, four to eight cocoon strands are connected and twisted together. They are then twisted together with several additional filaments to create a thread that is wound on a reel. The thread is called raw silk. It usually consists of \(48\) individual silk fibres. When each cocoon is unwound, it is replaced by another cocoon. Unlike the thread spun from other natural fibres such as cotton or wool, the silk thread is made of extremely long fibres. About \(5500\) cocoons are required to produce \(1\,{\rm{ kg}}\) of raw silk.

Note: It must be kept in mind that about \(1\) per cent of the total harvest of cocoons is not boiled. The insects within the cocoons are allowed to mature to form silk moths. These silk moths cut through the cocoons and are allowed to breed silkworm eggs for the future production of silk. The silk from the damaged cocoons is collected and mixed with the filaments of the coarse outer portion of the cocoons and the inner portions of cocoons which are left after reeling. This mixture is then spun to obtain low-grade silk yarn.

Processing of Silk thread from Silk fibres

The processing of silk is twisting one or more threads of the raw silk into a strand sufficiently strong for weaving or knitting. This procedure is called throwing. In the process of throwing, \(4\) different types of silk thread can be produced.

Organzine: Organzine thread is made by giving raw silk thread a preliminary twist in one direction and then twisting two or more of these threads in the opposite direction at a rate of about \(4\,{\rm{ turns}}/{\rm{cm}}\).

Crepe: Crepe is similar to organzine but twisted to a greater extent, usually \(16\) to \(32\, {\rm{ turns}}/{\rm{cm}}\).

Tram: Tram is made by twisting two or more raw silk threads in only one direction with \(\)8 to \(12\, {\rm{ turns}}/{\rm{cm}}\).

Thrown singles: Thrown singles are individual raw silk threads that are twisted only in one direction. The number of turns depends on the quality of the thread required.

In the production of silk fibre, organzine thread is generally used for the warp and tram thread is used for the weft or filling. The crepe thread is used in the weaving of crinkle silk fabrics. The thrown singles thread is used for weaving shear silk fabrics.

Wild Silks

Several undomesticated silkworms produce wild silks. The wild silks differ in colour and texture from the domesticated silk variety. Furthermore, the cocoons which are gathered in the wild are usually chewed through by silk moths. Thus, the single thread which makes up the cocoon has been cut into shorter lengths. A few other varieties of silk based on the month species include eri silk, tassar silk and mooga silk.

The beautiful and expensive golden coloured wild silk called mooga is produced only in Brahmaputra valley, mainly Assam and adjoining parts of Burma. This variety of silk is the strongest natural fibre, which actually improves with ageing and washing. Garments made from it outlast those made from ordinary silk – commonly lasting \(50\) years or more.

Uses of Silk

1. Silk fabrics are lightweight, lustrous, soft, elastic and highly strong in tensile strength. It keeps warm in winter and cools in summer.
2. Silk is commonly used to make expensive dresses for men and women, which are worn on special occasions. In India, most of the silk is used in making sarees and scarfs.
3. In addition to clothing, silk is used for items such as parachutes, bicycle tyres, bulletproof vests, and non-absorbable sutures in surgery.

Summary

Silk is also an animal fibre produced by certain insects to build their cocoons and webs. It is one of the oldest known fibres, and we find it useful in China in the \({27^{{\rm{th}}}}\) century \({\rm{BC}}\). The silkworm moth was found only in China, and for about \(3000\) years, it was a secret known only to the Chinese.

Other than moth caterpillars, many different types of insects produce silk. But, the mulberry silkworm or the species Bombyx mori, is used for commercial silk production. Tussar silk is produced by a species of silkworms that feed on oak leaves and, Dupioni silk is produced by a species in which two silkworms spin a cocoon together and produce a double thread. In this article we learn about the history, properties, processing and uses of silk.

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