Silk --A History of Beauty

The discovery of the silk threads by the silkworm species `Bombyx Mori' was believed to be during 2700 BC. According to a Chinese legend, the bride of Emperor Huang Ti, a 14-year-old girl called Hsi Ling Shi, discovered how to harvest and spin silk thread from the silkworm. Since then, the art of harvesting silk threads and spinning silk cloth extended to regions far and wide, and became then one of the world's most valued commodity. In 139 BC the world's longest trade route was established from Eastern China to the Mediterranean sea. This route was named the ``Silk Road'' after this much sought-after commodity. By 300 AD the secret of silk production had reached India and Japan.

The knowledge on how to produce silk material eventually reached Europe and America. During the 18th and 19th centuries the Europeans made several major advancements in silk production. By the 18th century England led the rest of Europe in the manufacture of silk cloth due to English innovations in the textile industry. These innovations included improved silk-weaving looms, power looms and roller printing. In 1870 an epidemic called the Pebrine disease, caused by a small parasite, wrought havoc on the silk textile industry. It resulted in added research on silkworms and ultimately set the stage for a more scientific approach to silk production. Silk production today exists as a combination of old and modern techniques.

Main Industry in Thailand, Japan & China There are two forms of silk production, the first is employed in Thailand by mainly largely by peasant farmers who reel the silk by hand. The other more industrialised method involves a reeling machine and this process is used in Japan and China.

Thai Silk Production
The Thai silk moth is used to tropical conditions and produces at least ten batches of eggs each year. Silk from the Thai moth is reeled by hand from green cocoons. These are cocoons that still contain the live pupae. The small cocoons which do not have the pupae are 'stifled' or killed before the thread is unwound or else the thread would be difficult to reel. The green cocoons are placed in boiling water, which loosens the end of the thread. Within 10 days (before the moths emerge and ruin the cocoon) the thread must be harvested and processed. This complex procedure has limited the amount of silk thread produced daily. Even experienced workers rarely produce more than 300kg/day.

Chinese & Japanese Silk Production
The moth favoured in China and Japan is `monovoltine' or `bivoltine', which annually produces one or two batches of eggs respectively. The eggs then enter a diapausal state (suspended development) and can then be treated to induce hatching at a commercially convenient time. These cocoons are large and the thread is reeled by the reeling machine which produces a continuous filament usually between one and two kilometres in length. The adult moths retained for reproduction purposes are too fat to fly as the best fliers to not produce as much silk. The stifled or dead pupae are usually composted to feed the mulberry trees. Whilst the tropical silkworm favoured by Thailand is a natural, hardy creature quite capable of surviving in the wild, in China and Japan, a specific type of silkworm is farmed (one that produces the maximum output with minimum cost). The average yield of raw silk in Thailand is 26kg per hectare. Korea produces 80kg per hectare and China 125kg per hectare.Silk production is an extremely `big' business.

Silk - A Hardened Glandular Fluid
Silkworms possess a pair of special saliva glands called silk glands or sericteries which are used for the production of silk cocoons. These glands secrete a clear, viscous, proteinous fluid that is forced through openings called spinnerets on the mouthpart of the larva. As the fluid comes into contact with the air it hardens. The diameter of the spinneret determines the thickness of the silk thread.

Silk Thread
The silk is a continous filament fibre consisting of fibroin protein secreted from two salivary glands in the head of each larvae and a gum called sericin which cements the two filaments together. Silk must be reeled off the cocoon quickly before the pupae begin to rot and taint the thread with unpleasant smells. Cocoons are then softened in hot water to remove the sericin which frees the silk filament ends for reeling or filature. Single filaments are drawn from cocoons in water bowls and combined to form yarn. This yarn is drawn under tension through several guides and eventually wound onto reels. The yarn is dried, packed according to quality and is now raw silk ready for marketing. The worn and withered body of what was intended to become the wondrous flying creature that is the butterfly slips silently away.

Fibre Properties
Silk is a natural protein fibre containing about 75% of actual fibre fibroin and about 35% sericin which is a gummy protein that holds the filaments. Silk filaments are very fine and long - as much as 300-900 metres long. Silk has a high natural luster and sheen of a white or cream colour. Silk is one of the strongest fibres of 2.4 to 5.1 grams per denier. When it is dry the elongations (elastic recovery) varies from 10-25% and when wet it will elongate as much as 33-35%. Silk has a relatively high standard moisture regain of 11%. At saturation the regain is 25-35%. Silk can be dyed before or after it has been woven into a cloth. It can be woven or knitted. Types of Silk Next the raw silk is twisted into a strand sufficiently strong for weaving or knitting. This procedure is called throwing. Four different types of silk thread may be produced from these procedure: organzine, crepe, tram and thrown singles. Organzine is a thread made by giving the raw silk a preliminary twist in one direction and then twisting two of these threads together in the opposite direction. Crepe is similar to organzine but is twisted to a much greater extent. Tram is made by twisting in only one direction two or more raw silk threads. Thrown singles are individual raw silk threads that are twisted in only one direction. In general organzine thread is used for the threads of the materials, tram threads for the weft or filling, crepe thread for weaving crinkly fabrics and a single thread for sheer fabrics. Broken or waste filaments and damaged cocoons are retained, treated and combed, to be processed into yarn, which is then marketed as spun silk. This silk is inferior to reeled silk and much cheaper. Similar with the production of any other material, nothing is wasted and spun silk is also produced to be sold as a cheaper and poorer copy of reeled silk. After the silk is harvested from the cocoons it is brought to the weavers for dyeing and preparation for weaving. Previously insect and plant dyes were used but today, chemical dyes are used. Low grade silk is made from damaged cocoons, which were `spoiled' as the worms began to emerge earlier than expected. These cocoons are then used for breeding. Filaments from the coarse outer layer of the cocoon is removed by brushing them and then they are reeled. This raw silk is then mixed with silk from the damaged cocoons to make low grade silk. Another product, which has now almost been completely replaced by nylon, was from the silkworms' carcasses. In this process, before the pupae were allowed to weave their cocoons, they were unceremoniously immersed in acid. Their bodies were cut open and the thread was removed from their silk glands. This 'gut' was once used by surgeons to stitch up patients and also by anglers to be used as fishing lines.