Tasar Silk


Present status of Tasar Raw silk production with special reference to Bihar
  It was observed that Tasar Raw Silk contributes 16% in Vanya silk and 1.78% in total raw silk production during 2005-06 in India which is comparatively
lower than 2004-05.
  Bihar was leading state in Tasar silk production in India before division in Nov 2000 and its share was recorded approx. 50% 1989-99. Bihar is placed at seventh rank among tassar producing states in India.
  Main Tasar cocoon producing areas are namely viz; Bhabhua, Rohtas, Nawada, Jamui, Banka and Munger. There are two Tasar Pilot project centers and 12 Tasar seed supply sub stations in Bihar.

Cultivation of silk, processing silk cocoons, spinning of silk yarn
Silk is a strong, soft, lustrous fibre extruded by certain kinds of moth and spiders. The popular variety of cultivated silk is Mulberry. There are other less-cultivated species, so-called wild silk, such as tassar, feeding on oak leaves which find its home in Central India-Bihar, Jharkhand, Orissa and Madhya Pradesh.

Cocoon Harvesting & Preliminary Sorting
When the tassar silk worm has completed the process of eating and growing it continues to spin its protective layer for the pupal stage known as cocoon. By moving its head in the pattern of figure “8”, the silkworm continues to spin its spinning process non stop till it completes the formation of a fully built cocoon. During the cocoon spinning the silkworm is left undisturbed as a slightest of hindrance might cause the silkworm to die.
The spinning of cocoon by tassar silk worm larva is completed after 4-6 days of its commencement and the larvae inside pupates after another 4-6 days. The total period involved till pupation is nearly 8-10 days when it is fit for harvesting. During harvesting itself preliminary sorting of cocoons is done. Healthy seed cocoons are utilized for reeling and unreelable cocoons like flimsy, pierced, pinhole, double deformed cocoons, cut cocoons etc. are taken for producing variety of spun yarn.



Stifling
Stifling is the process of choking fresh cocoons and to prevent the emergence of moth in the form of butterfly by killing the pupae inside and also to ensure proper preservation of cocoons by eliminating the cocoon moisture and making the cocoons suitable for unwinding. Cocoons are preserved and stored by traditional methods i.e. Sun-drying.

Sun Drying
Cocoons are spread floor in heated sun light for several days till the pupae are killed and cocoons are completely dried. It is simple, economical & requires no initial investment. It requires labour, space and prolonged exposure to sunlight. Sun drying is necessary after stifling for proper preservation of cocoons. Storage of semi wet cocoons causes fungus attack and vitiates reeling efficiency, requires additional labour and time

Selection of Cocoons for Spinning


To facilitate optimum recovery and better quality product from these cocoons, they are selected from the lot based on their physical and commercial characters. The uniform softening or cooking is obtained by adopting appropriate softening or cooking method. Prior to softening, cocoons are sorted separately.

Colour
It is a prime character and is due to the presence of colouring pigments. Normally the tassar cocoons are either yellow or grey. Grey cocoons are better than yellow ones in respect of silk content.

Compactness
The extent of tightness and hardness indicates the shell texture of cocoon layer. The air and water permeability of cocoon during in boiling is largely dependent upon the hardness of cocoon shell. More compact cocoons require more boiling time with higher concentration of chemicals. Freshly harvested cocoons require less time as compared to old aged cocoons.

Size
Tassar cocoons can be graded into large, medium and small according to the size range. Cocoon lots of uniform size and built are cooked together.


Shell weight
The cocoon shell is closely related to the raw silk yield. Heavier the cocoons with thinner shell will get over soft compared to thicker shell cocoons or thicker shell cocoons may remain hard and become unfit for reeling and spinning. After having sorted the cocoons of more of less similar physical & commercial character are cooked together by an appropriate method for reeling and spinning.


Cooking (Boiling) : Traditional Method

Traditionally tassar cocoons are cooked in an earthen pot at or near boiling sodium carbonate (washer man’s soda) solution for 4-6 hours. Cocoons are then reeled in semi moist condition on Natwa/Thigh, where the productivity per day per reeler comes to about 60-80 g of 60 D silk yarn.

Spinning
Spinning is the process of formation of yarn by a combination of drawing/drafting, twisting and winding operation either in continuous or intermittent, applied to prepare fibre mass. Traditionally there are 3 type of tassar spun yarn viz, Ghicha, Katia & Jhuri. These yarns are produced out of tassar silk waste obtained during various stages of tassar silk processing. Tassar silk spinning process on Ambar Charkha is very popular. It is appropriate and up to date method which gives higher productivity and finer yarn with more uniformity as compared to other spun yarns.

Tassar waste spinning
Bhagalpur in Bihar is known for producing fine and coarse quality exportable handloom fabrics. At the time of reeling the cocoons of tassar, muga, eri silks. The byproduct and waste are used very carefully to spin the yarns like Ghicha, Katia and Jhuri etc.
Normally good tassar cocoons are reeled. The filament a cocoon is at most 60-70% reelable. The left-over portion is spun. The pierced and inferior quality cocoons as well as those which have been spoiled by improper cooking or reeling are used for spinning. The ratio of reeled and spun yarn produced in tassar silk production in India is about 50:50.Some waste is generated during the process of the reeled yarn as well as during the spinning of the waste silk.The waste silk is thoroughly cleaned and spun into yarns. Spun silk is produced from waste with long staples, which gives yarn its characteristics brilliance. Short-stapled from waste from the comber noil is used for spinning noil or blended yarns. These yarns are coarse and lack the characteristic brilliance. The tassar silk wastes used for spinning come mainly in the following forms:
Cocoons waste
Pierced cocoons are the best quality waste. Defective cocoons, e.g. showing black stain, rust, mutes, spots, thin ends, loose knitting, mould, doubles etc. are not suitable for ordinary reeling and form an inferior type of waste. They are used for producing tassar spun yarn.
Peduncle waste
The hard-shelled tassar cocoon is provided with a black well-formed peduncle and ring. Normally the peduncle length is about 4cm in male tassar cocoons and 5.7cm in female. The average specific gravity is 1.362. Prior to cooking the operation of peduncle cutting is necessary. The peduncles are utilized to form a special variety of tassar waste yarn.
Deflossing waste
In order to find out the true end of the filament, the outer surface floss layer of tassar cocoons is removed. This is entangled and coarse and does not yield silk for reeling. It has high gum content and regarded as good quality waste.
Reeling waste
In the course of reeling the reelable filaments are converted into waste in finding out true ends from cocoons after breakage. It can be spun by hand or on a charkha. The innermost layer of cooked tassar cocoon is not reelable. This also forms a part of poor type of reeling waste, which can be converted to spun yarn.
Thread waste
During the process of re-reeling winding, doubling, twisting, warping and weaving, the thread wastes are obtained. These are mechanically processed in the spinning operation.

The following hand spun yarns are produced from tassar silk waste:
Ghicha yarn
This is obtained mostly from pierced, cut, flimsy, insect damaged and double cocoons. The cooking process for the production of ghicha yarn is the same as for the reeled yarn produced from good cocoons. Cooked tassar cocoons which are unreelable owing to opening of the peduncle end or a hard shell are also used to produce the hand-drawn coarse yarn called ‘ghicha’. Here a bunch of thread is pulled out by hand from one or two cocoons at a time and reeled on an earthen pot. This gives a coarse variety of untwisted thread of 4s to 6s. Finer ghicha as high as 30s can also be spun. Ghicha yarn is used as weft for the production of various union fabrics in combination with reeled silk or Katia or even with cotton.
Katia yarn
Katia yarn is obtained from the tassar silk waste left after reeling, including floss. It is normally spun on charkhas or spinning wheels with a count of 15s to 30s. The yarn is given sufficient twist and is strong enough to be suitably used for warp. Katia yarn is mainly used for the production of wrappers and other thicker varieties of dress material.
Balkal Yarn
Balkal is a thick coarse yarn spun from tassar peduncles. The peduncles prior to spinning are subjected to cooking and opening operations. Peduncles are boiled in soap and soda solution followed by steaming. After washing and drying, they are beaten-up for opening and subsequently carded and finally spun into thick yarn upto about 10s by either a spinning wheel or Ambar charkha. The degumming loss of the peduncles of different races of tassar cocoons is shown in Balkal yarn is normally used as weft in combination with reeled silk for the production of union fabrics.
Jhari yarn
This yarn is spun from uncleaned and unopened tassar waste.
Mill spun yarn
Tassar waste material contains a considerable amount of gummy materials which hinder the subsequent mechanical processing in a spun silk mill. Tassar silk waste is degummed by boiling in a pressurised tank with soap and soda for 30 min and treated with sodium sulphite for partial bleaching. However, to remove gummy matter completely, the material is subsequently kept in a soap and soda solution in a large wooden tank for 3-4 days. After degumming the material is fresh water, hydro extracted and subsequently dried in hot air chambers. The degummed tassar waste is then processed through a series of operations which includes opening, filling, dressing or combing, spreading, drawing, gill roving, spinning and gassing. Mill spun tassar yarn in the range of 60-210s (metric count) can be produced. The yarn is then doubled and twisted according to the required specifications.

The flow chart in involving above steps are summaries as under:
Cultivation of Silk, Processing of Silk Cocoons, Spinning of Silk Yarns


Weaving preparatory process : reeling, twisting, sizing, warping, drafting

Tassar silk reeling
The process of unwinding of filament from the cocoons and their combination in a composite reeled yarn is termed as tassar silk reeling. An elaborate series of processes is involved in obtaining tassar silk reeled yarn from the thick hard tassar cocoons. Tassar reeling is not carried out in filature like mulberry cocoons. Mostly it is done in small quantities by the womenfolk of weaver’s family. Prior to reeling, cooking (the term is most commonly used instead of “degumming” in sericulture industry) is necessary to make cocoon shell fairly soft, thereby facilitating the smooth unwinding of the filaments.
Traditionally Tassar silk reeling is generally conducted by the women folk of weavers’ family on thigh. It is not only a slow and crude process but also unhygienic. There is also the process of spinning the tassar yarn.
The fibres especially natural fibres contain miscellaneous things that are derived from nature. These are pectin, grease, wax, colour tone, inorganic substance etc. Moreover there are secondary impurities like oil agents, warp starch etc. that make the weaving and twisting easy. These impurities not only obstruct dyeing but also prevent the fiber from generally, tassar cocoons require more drastic treatment in cooking than mulberry cocoons. This system is also practiced for reeling inferior quality cocoons including emerged cocoons which cannot undergo machine reeling.

Dry Reeling Process : Thigh Reeling

The thigh-reeling system is an old and unhygienic system of reeling in which rural woman, sitting on the floor cross-legged, draw 5 to 6 filaments on their thigh from cocoons cooked by alkaline method, twist is imparted by the left hand with a little a additional of ash powder, oil and starch. Composite reeled yarn is wound on a bamboo-made hand appliance called the traditional Natwa (Photograph) in the villages. Cocoons are also reeled on charkhas.

Tassar silk reeling on traditional charkha


The cocoons cooked with Hydrogen peroxide (H2O2) cooking method. It yields yarn with better cohesion & makes it possible to reel on simple hand operated tassar charkha in dry basin. In this charkha reeling the composite filaments from 6-7 cocoons are passed into one to form the yarn.


Modified Reeling Approach
During the cooking process of thigh and machine ling (dry), the gummy materials are removed to a large extent. Exhibiting its merits fully thereby harming the quality of the yarn. Thus, it is necessary to eliminate them beforehand prior to chemical processing.

Reeling is the process of transferring yarn from one form to another suitable form. During the process the yarn faults such as cracks, clusters, neps, thick and thin places etc. If any are removed manually. For the purpose the above said tassar reeling charkha also could be utilized.


Pre-weaving Activities
In general, preparatory to weaving have the following sequence:

Winding involves transferring raw silk from natwa to the warpers natwa (Ughra) of 4-5 inches diameter after combining 8 number of ends together, warping is made by running the threads by walking from one point to other after proper leasing. In many places other warping methods like peg warping (single or 8 ends), cage warping, horizontal or vertical drum warping method are also practiced.
The warp thread is then made in to a bundle form and dipped into a sizing bath for over night, containing following traditional recipe:
  (1) Rice extracts 1 kg.
  (2) Rice powder 150 kg.
  (3) Soap stone powder 400 grams.
  (4) Coconut oil 50cc.
  (5) Mustard oil 50cc.

The soaked warp bundle is taken, squeezed and rinsed carefully and spread in an open place. Fresh sizing liquor prepared from the above recipe with little boiled TKP is sprinkled over warp by brush. Sprinkling and brushing over the warp is repeated several times. After this drawing and drafting of thread is made, after proper beaming, weaving is conducted on pit loom. This traditional system requires special skill and attention of the weavers to perform all the operations. It requires 7 to 8 persons to carry out the whole process. The soaked hanks are squeezed by hand to remove excess solution. Hanks are than rewinded onto the swift and allowed to dry.
The reeled bobbins are converted into hank form. These hanks are soaked in a size solution containing the following ingredients. Now a day the chemical size solution is prepared as under:
Size recipe:
Sago 5% as main adhesive
Vegetable Tallow 1%
Zinc Chloride 0.1%
Material: Liquor ratio 1:20
After weighing required quantity of sago is soaked in plain water for about 1-2 hrs for swelling. Then it is boiled till it gets completely dissolved in water. The solution is filtered using fine cloth to remove lumps if any in the solution. Vegetable tallow and Zinc chloride are added and mixed thoroughly by stirring the solution followed by boiling for 10-15 minutes. The solution is allowed to cool and ready to be used for soaking. Thus yarn so produced is used for warp.


Twisting
The yarn is twisted for binding the holding filaments of yarn together thereby improving the strength of yarn. The level of twist to be inserted depends on the type of fabric to be produced.
Traditionally, twisting in the conventional method is done by spreading the 6-8 single yarn parallel to each other. Each free end is hung by spindle and takli rotated by hand and twist is allowed to flow upto the rear end of the yarn. After insertion of twist, the twisted segment is wound on to the bobbin and again the process is repeated for following segments from the supplying form. In carrying out this process 3-4 persons are engaged and thus the tassar yarn is twisted. As the process is intermittent the twist is not uniform Moreover, it is also requires a large floor space. Due to use of such long space the twisting is usually carried out on village path lanes which create inconvenience to passersby. During the rain and in scortching sun the twisting operation is abandoned by the operators, thereby depriving them of their wages. In Bhagalpur the tassar yarn is doubled or plied for use in fabrics to render the strength.


Warping of yarns / Preparation of beams, drafting
The sized yarn of predetermined length is wound on warpers bobbin and mounted on warpers creel. The number of warping bobbins depends on the number of ends per section. Later the threads are collected and passed through leasing dent and condensing dent making a section to be wound on weavers beam.
After a required length of the section is wound, a number of such sections are wound on the beam depending on the total number of ends required in the width of fabric to be produced. Thereafter drawing and drafting through healds and reed is done. The drafted beam is then taken on the handloom for weaving.


The flow chart involving above steps are summarized as under:


Weaving of silk fabrics
Tassar silk weaving is totally traditional. It is carried out mostly on pit loom to a large extent and fly shuttle frame loom, for makingwoven designs on the fabric dobby or Jacquards are attached on these looms.
There are few developments over these looms wherein some of the loom motions are operated by weaver while other are mechanically operated. Some of the improved handlooms commonly used for tassar weaving are Banarasi fly shuttle loom. Nepali handloom, Chittaranjan semi automatic handloom etc.


Wet processing of tassar silk
The natural colour of tassar fabric is generally kept as such for domestic and external marked but for elegant look and verity of choice it requires a camouflaging. This change is brought about by certain treatment on the silk which generally includes degumming, bleaching and dyeing. The removal of gum or sericin is an important treatment during the processing of silk as the presence of gum makes silk harsh and of stiff feel.
Degumming is the removal of the further gum/sericin. It also hides the whiteness and lusture of the silk. The presence of gum also hinders dye absorbtion during the dyeing/printing process. The conventional method of degumming is carried out by boiling the yarn or fabric in non-ionic soap (natural soap) with a small quantity of soda ash for about 2 hours.

First bath : soap (neutral) 15%
soda 5% boiling 1 hr
Liquor ratio 1:4
Second bath : soap (neutral) 15%
soda 5% time 15 min in 80c
Liquor ratio 1:4

The fibres especially natural fibres contain miscellaneous things that are derived from nature. These are pectin, grease,wax, colour tone, inorganic substanance etc.Moreover there are secondery impurities like oil agents, warp starch etc. that make the weaving and twisting easy. These impurities not only obstruct dyeing but also prevent the fiber from exhibiting its merits fully thereby harming the quality of the yarn. Thus, it is necessary to eliminate them before hand prior to chemical processing


Degumming machines
Silk is degummed both in the yarn as well as fabric form. Since the silk processing is largely carried out in the small scale industry, manual methods have been quite popular. Lately many machines with electronic controls have been development.
Yarn
1. Boiling in loop in open becks
2. Foam method
A.) Boiling in loop: tank method
In this the hank are hung on polished wood or metal rods which are submerged in the bath and turned manually. The soap bath prepared in the tank is heated by closed/ open steam pipes and brought near to boiling point. The skeins hang on a smooth wooden rod resting on the side of the tank, immersed to about three-quarters of their length for about half an hour, by frequent turning of the rods, are evenly soaked throughout their full length. The solution charged with a great part of the sericin and other impurities is then drawn-off. The skeins are washed in softened water for complete elimination of soap, and centrifuged.
Bleaching
Although degumming of silk removes the major portion of the colouring matter the silk especially tassar needs further bleaching in error to improve the whiteness and appearance. This is carried out by the usage of H2O2 alongwith soda ash or sodium silicate or ammonia solution as buffer. The bleaching reaction is carried out for about 2 hours.
Chemicals used for degumming & bleaching (single stage)

Soda ash 2.5% (% on wt. of goods)
Sodium silicate (110 Tw) 1.5%
An lonic wetting agent 2.0%
H2O2 (50% w/w) 15.0%
ML ratio 1:30
PH 9.0
Temp 80c
80c 2hrs

However, It is further to be noted that bleaching of tassar silk is generally carried out with the following recipe

H2O2 (30% w/w) 12cc/lit.
Sodium silicate 2 gms/lit
Sodium perborate 1gm/lit.
Liquor ratio 1:40
Time 12 hrs.

A bath is prepared with the aforesaid recipe and the degummed silk is put in the bath at 60c initially and left at room temperature for 12 hrs. Later the silk is washed and dried.
Dyeing
The dyestuff applicable for the mulberry silk is also be applied for tassar silk by following the same technique. Natural silk requires approximately twice as much dye as wool to get some depth of shade. The flatness of tassar fibre exaggerates this even more. Higher the concentration of dye in the bath the less is the change of uneven dyeing. This rule applies by the large to natural silk but since the high concentration of dye only produces relatively pale shades on tassar, the possibility of getting uneven result is quite high.
Dyeing of silk is generally carried out with Reactive (cold and Hot) and Acid dyes stuffs
Reactive dyes
It gives expetionally good colours to natural silk say dye stuff 4% Glaubers sakt 60-80 gm/lit.

Soda ash 2 gms/lit
Liquor ratio 1:75
Tempearature 80-85*c.

Silk matarial is immersed in dye bath at 50*C containing glaubers salt and soda ash and stained for 10 min. Then the well dissolved dye solution is poured into the bath and then temperature is raised to 85c. The dyeing is further continued for another 45 min. After dyeing the material is washed in cold water and then it is soaked in solution of 2 gm soap/lit at 70c/ for 20 min. The material is finally washed and dried.
Acid dyes
Acid dyes recipe
Dye stuff 2-3%
Glaubers salt 10%
Formic acid 3-4%
Time 1 hrs
Temperature- boiling
Liquor ratio 1:75

Nowadays the weavers are adopting the process of cold dye but the results are not after guaranteed.


Finishing
Finishing is an important factor for marketing of the finished commodities. Tassar finish is generally conducted by two techniques to improve the cover. Feel, lusture and look of the fabric. These are dependent on the type of finish. There are two types of finish which are as under:
1. Kundi finish i.e. Beating with wooden hammer
2. Calender finish
Kundi finish is very common mostly done in all export varieties of tassar fabrics manufactured for domestic market. Calender finish no doubt is very good and methodical but it is only applicable if continuous length of a fabric is available and as such calender finishing is very rare in tassar silk industry.
Kundi finish
This is an indigenous practice of fin shining of silk fabrics. After bleaching the cloth is washed well in cold water and then it is treated into the finishing bath having the following recipe for 50 saree pieces.

Kalatek J 1200 gms.
Stabliser C 50gms.
Arrowrot powder 50gms
Glycerine & I.R.O.i little amount
Temperature Room temperature


Calender finish
This finish consists of above recipe and passed through the steam heated calenders at a slow speed after which the cloth pieces are folded properly and packed. The calender finish is generally of material is finished at a time.
The aim pursed in silk finishing is to reveal the properties, i.e. lustre, handle, drapability etc. The finishing of tassar silk is not a common feature. However, depending upon the specific requirements, chemical or mechanical. Generally the fabric is soaked in the finishing chemicals and squeezed manually or the chemical are sprayed onto the fabric.
Machanical Finishing
Dried tassar fabric can be moistened and wrapped with cotton/silk fabric and hammered manually by to wooden hammers alternately to impart a soft handle and lustre. This process is known as Kundi finishing and can be compared with a button or knife breaking machine finish, where fabric is passed several times rapidly back and forth over small rollers studded with brass buttons or slanted knives. Tassar silk fabrics can be calendedred on a two bowl calendering machine for improving handle and appearance.


Printing
Bihar is a large producer of tassar or tussah silk. The region also produces mulberry silk. Cottage industries in Bihar include sericulture, handweaving, printing, and finishing. Bhagalpur in Bihar is well-known for the printing of silk saris and bed covers. Prior to printing, the fabrics are washed in a locally produced iron-free soap. Printing is done with blocks smeared with color. The blocks are produced by local artisans using their own designs. The dyes used for printing are acid, metal complex acid, or direct dyes. The printing pastes are stored in special wooden containers. Printing is done on a heavy table. After printing, the fabrics are dried, steamed, and wrapped in unbleached cotton. Shanada prints, Patli prints, Koria prints, Pancha, and other design motifs are discussed.
Printed mulberry silk fabrics are popular due to the exclusiveness of designs and coloristic effects that can be achieved. But this is less in the case of tassar silk because of its inherent colour and a lack of available technological knowledge in the trade. However, the success depends to a great extent on proper pretreatment such as desizing and bleaching.
Direct Printing
For printing of tassar by direct style, acid metal-complex, direct and reactive dyes are normally used
Printing may be carried out by screen or block printing method. In case of block printing the thickener used is gum Arabic. The printed fabric is dried under mild conditions to retain a good printed mark and prevent the goods from marking off during subsequent process. Steaming is carried out in saturated steam for 45-120 min. depending on the steamer used. Washing is carried out under mild alkaline conditions with a standard detergent to prevent the re-adsorption of washed dye onto the fabric. The fabric is neutralized and dried at low temperature.


Ironing
Finally the finished product goes for ironing and packaging.

Tassar silk processes: Flow Chart
The flow chart indicating the processing involved in weaving, wet processing are summarized as under: