Sericulture industry is the combination of agriculture, animal husbandry, cottage industry and pure textile activities. The quality of end products directly relates to any minute variations taking place in all these varied phases, which calls for careful planning, skill requirement and an effective delivery mechanisms at the governmental and private sectors. There are many activities termed as components in the silk industry.
Food Plant Cultivation
Mulberry, the food plant of mulberry silkworm is cultivated following the prescribed package of practices evolved by the research institutes over the years. Mulberry is a perennial crop which can easily give yield for 25-30 years. Mulberry grows in almost all types of soil, but the plantation requires sufficient exposure to sun, organic inputs and availability of water in sufficient quantities. Mostly mulberry is cultivated in bush form and in some areas as trees. It is generally pruned twice in a year and the leaves can be harvested five times in a year.
The food plants of the non-mulberry silkworms are mostly found in the nature. However, systematic plantations of some of these food plants are done in many countries to enhance productivity, thereby making the avocation economically viable. These food plants are cultivated in forest fringe areas and other places which are found to be unsuitable for food crop cultivation.
Mulberry silkworm rearing is generally conducted in indoor as an animal husbandry occupation. The rearing is a complex process wherein the various factors like, temperature, humidity, leaf quality, rearing house, control of diseases, etc., play a vital role for a successful crop. The leaves or twigs are brought from the field and feed to the silkworms in separately erected platforms or trays. After the gestation period of about 25 to 28 days, the matured worms are picked up and transferred into the mountages for spinning the cocoons. The spinning process will be completed within three days and the cocoons can be harvested for marketing after five days. The mulberry and eri silkworms are reared in this fashion in separate rearing houses.
In case of Tasar and Muga, the young age silkworms are transferred to naturally grown trees to feed on the leaves and to form cocoons there itself. The gestation period of the rearing is about 30 days. The cocoons are then harvested manually by the farmers.
|Healthy seed is the backbone of sericulture industry. Poor seed health is the primary reason for poor productivity. Seed, at the same time, may act as one of the main vehicles for dissemination of diseases. Seed-borne pathogens, such as protozoa, fungi, bacteria and viruses are serious constraints to sericulture industry. Hence, healthy seed material, free from diseases and having high viability is essential for establishing the crop in the first instance. And also availability of quality silkworm seed in adequate quantities is the pre-requisite in achieving the targeted silk production besides improving upon the productivity parameters. To produce quality seed, it is very important to adopt scientific methods of egg production right from seed crop rearing to egg incubation.|
|The silkworm seeds are produced through a four-tier seed multiplication network to retain the inherent genetical characters like hybrid vigour and disease freeness. While the breeders stock is supplied by the R & D institutions (first level), the basic seeds in the next three levels are produced in different basic seed farms. The commercial seeds are produced in the seed multiplication centres from the F1 seed supplied from the basic seed farms.|
The seed is produced in specially designed buildings called as Seed Production Centres. There are various production processes like cocoon selection, cocoon preservation, ovi position, egg laying, moth examination, etc. In case of the nucleus and basic seed production units, separate plantations are maintained for undertaking seed cocoon rearing. For the production of commercial seeds, the seed cocoons are mostly reared among the seed cocoon farmers.
Reeling is the process at which the compact untwisted and undegummed silk thread is formed by combining the required number of silk filaments drawn from as many separate cocoons by a special technique. There is a series of skilled operations dealing with the raw material which is composed of extremely fine continuous silk filament of great length unlike other natural textile fibres. Reeling demands constant attention and care on the part of the reeler since during the process of reeling the cocoon filament may break continuously and the reeler must properly attach and fresh filament which is always kept ready in reserve. However nowadays with the introduction of Automatic Reeling Machines, there is an automated system to pick up the cocoons during the breakage of cocoons.
The art of reeling is believed to have originated in China nearly 3000 years back. Reeling is generally done as a cottage industry in most of the developing countries. Different types of machines are used for the reeling activities. The most recent one is the Automatic Reeling Machines (ARM) which are very famous in China. But, the countries like India and Thailand, the traditional machineries like charkha, cottage basin and multi-end reeling machines continue to dominate the reeling industry.
The Muga and Tasar silks are also generated through silk reeling. However, Eri silk yarn is produced by spinning of cut cocoons.
In most of the countries cocoons and raw silk are transacted through Government owned cocoon markets silk exchanges to ensure transparency and fair pricing in trading.
Silk throwing is the industrial process where silk that has been reeled into skeins, is cleaned, receives a twist and is wound onto bobbins. The yarn is now twisted together with threads, in a process known as doubling. Colloquially silk throwing can be used to refer to the whole process: reeling, throwing and doubling. Silk had to be thrown to make it strong enough to be used as ‘organizine’ for the warp in a loom, or tram for weft.
Wet process is usually done on the manufactured assembly of interlacing silk fibers, filaments, and/or silk yarns having substantial surface (planar) area in relation to its thickness, and adequate mechanical strength to give it a cohesive structure. In other words, wet process is done on manufactured silk fabric. The processes of this stream is involved or carried out in aqueous stage and thus it is called silk wet process which usually covers pre-treatment, dyeing, printing and finishing.
All these stages are required aqueous medium which is created by water. A massive amount of water is required in these processes per day. It is estimated that, on an average, almost 100 liters of water is used to process only 1 kg of silk goods. Water can be of various quality & attributes. Not all water can be used in the process; it must have some certain properties, quality, color & attributes for being used in the processes. Hence, water is a prime concerned in silk wet processing.
Weaving is the operation which creates a fabric by interlacing the wrap yarns (lengthwise) and the weft yarns. Weaving is carried out on looms, after a series of preliminary operations including warping and pirning. Weaving in silk industry is generally done in handlooms and powerlooms. The powerlooms are mostly prevalent in China. In India, 60% of the silk weaving is done on handlooms and the handloom products are geographically famous for its unique designs and weaving patterns. In Thailand, the handloom weaving is very strong and the designs produced by Thai weavers are exclusive and famous across the world.
Enormous improvements have been made in improving not only the machines but also the loom itself. Automatic weaving machines, machines for weaving wider fabrics, shuttle less looms, Jacquard looms, etc., are some of the advancements in this direction.
Dyeing is the process of adding colour to silk fibres, yarns, and fabrics. Dyeing is normally done in a special solution containing dyes and particular chemical material. After dyeing, dye molecules have uncut chemical bond with fiber molecules. The temperature and time controlling are two key factors in dyeing. There are mainly two classes of dye: (i) natural and (ii) man-made. Although, acid dyes have been traditionally used in silk, the trend is now changing with more focus on vegetable dyes. The ban on certain azo dyes in European countries has reasoned the exporters to pay more attention to the selection and use of dyes to exported goods.
Printing consists of transferring a pattern to the fabric. The printing is carried on the following manner:
Block printing - Raised parts of the block transfer the dyestuff to the fabrics
Roller printing - Fabric to be passed through the rollers engraved with design
Screen printing - A fine gauze is stretched tightly over a metal frame, and the design to be reproduced is transferred to the gauze. The pores in the gauze is partially blocked off allowing the dye stuff to be squeezed through the gauze where the design is to be printed
Discharge printing - Is the combination of dyeing and printing. While dyeing the fabric, those parts of fabric to be decorated are protected by resin which is later removed, and the ‘holes’ are printed over the design. Alternatively, the base fabric is completely dyed, the dye is then removed from the parts to be decorated, and the design is then printed over
Hand printing - A handicraft activity
Spray printing - The dyestuff is sprayed directly on the fabric covered with stencils
Warp printing - Only the warp yarns are printed before weaving
All fabrics have to be finished with the exception of pattern weaves. It is the finisher who gives satin its shimmering suppleness and its ‘hand’. Finishing gives a fabric the desired appearance and feel. There are numerous finishing processes, physical and chemical. Finishing includes treatments such as crease proofing, water proofing, fire proofing, etc.
Spun silk and silk noil
Silk waste includes all kinds of raw silk which may be unwindable, and therefore unsuited to the throwing process. The waste materials are partially boiled off to remove some of the gum, and are then carded and combed to make staple fibres parallel to each other. The resulting strips of fibre, silvers, are then transformed into yarn: the longer filaments become spun-silk, or schappe, and the shorter one silk noil.
|The double cocoons are reeled by special technique and give thicker, uneven silk yarn which when woven makes an irregualr appearance to the fabric. This fabric yarn is highly prized among the fashion designers.|
Raw Silk Testing
Raw silk is tested and graded according to specified and accepted standards before marketing. Testing has been done generally in the testing houses operated by the Government and private agencies. At present, the cocoon testing evolved by the erstwhile International Silk Association has been followed in the world.
The raw silk classification is based on the grade, which is derived from the denier (thickness of silk in value terms) and other tests conducted for the purpose. These grades are expressed in the order of 4A, 3A, 2A, A, B.
Types of silk fabrics
The major types are:
- Poult and faille
- Chiffon, organdie, voile, grenadine
- Composite or fancy weaves
- Reps, regencies, piques
- Ottomans, grosgrains, fluted fabrics
- Gauzes, bayanderes, tartans, etc.
- Brocardes and Lames
- Double damasks
- Jacquard velvet
- Pattern weaves
- Furnishing fabrics