Is Tussar Silk Inferior to Mulberry Silk ?

In a paper entitled  "Study of property and structural variants of mulberry and Tussar silk filaments" by professor Mohan Gulrajani, one can get several hints which may lead to the answer to the question.

"A glance at the typical tensile behaviour reveals that the stress-strain curve of these two varieties is distinctly different, in that tasar shows a clear yield point and very high elongation compared to the mulberry filament."

Conclusion 1:  Tussar silk can undergo significant stretching before permanently deforming.

The tusar silk stress-strain curve exhibits a clear yield point. A yield point is a point on the stress-strain curve where the material transitions from elastic deformation (where it returns to its original shape after the force is removed) to plastic deformation (where it retains some deformation even after the force is removed). This suggests that Tussar silk can undergo significant stretching before permanently deforming. 

Conclusion 2:  Tussar can stretch a lot before reaching its breaking point compared to mulberry silk.

The stress-strain curve of tussar silk also shows very high elongation compared to mulberry silk. Elongation refers to how much a material stretches before breaking. The fact that tussar silk exhibits high elongation means it can stretch a lot before reaching its breaking point compared to mulberry silk.

In contrast, mulberry silk does not show as pronounced a yield point and has lower elongation compared to tussar silk. This implies that mulberry silk is less flexible and may have a more limited ability to stretch before breaking compared to tasar silk.

Why there is a difference in their properties

One answer can  be density.  The density of mulberry is higher ( 1.35 g/cc) as compared to tussar ( 1.30 g/cc). This suggests a relatively poor degree of orientation and less order in Tussar, which gives to lower modulus and elongation behavior of tussar.

These values have their commercial and functional implications. 

Can Silk be Machine Washed

At least a study suggests so. 

A paper titled "Study of property and structural variants of mulberry and Tussar silk filaments" by professor Mohan Gulrajani has suggested this idea. 

Earlier research suggested that the wet strength of silk specially Mulberry reduces considerably when subjected to water during laundering. This happens because in an aqueous environment, the hydrogen bonds between the molecules break. These bonds are crucial for maintaining the structure and strength of the fibers.

However the paper suggests that " silks can be machine washed at 40-60ºC provided one uses appropriate washing procedures, such as the use of neutral detergents".

The results for both Tussar and Mulberry found that " the tenacity and elongation at break are not

significantly different in dry or wet state ". However there is slight decrease in modulus. The figure given below talks about the result. 

A reduction in modulus would make the fiber less stiff.

Modulus, specifically in the context of materials science, refers to the measure of a material's stiffness or rigidity. It indicates the ability of a material to resist deformation under an applied force. Modulus is typically expressed in terms of stress divided by strain, where stress is the force applied per unit area, and strain is the resulting deformation.

When the modulus of a material decreases, it means that the material becomes less resistant to deformation for a given stress. In other words, it becomes more flexible or less stiff. Conversely, an increase in modulus would indicate that the material becomes stiffer or more resistant to deformation.

Then why it is not advised not to launder Pure silk sarees ?

The answer lies in the properties of commercially available silk fabrics or sarees. The above study was done after fully degumming the yarn. However, in commercially available silk fabric, the yarn is not fully degummed, there is always a residual gum or sericin. In the study about 20% sericin was found in mulberry and 5% in tussar.  On wetting, the sericin weakens, and allows inter filament slippage, which in turn leads to a drastic reduction in mechanical properties. Hence the strength of the wet silk gets reduced. 

What is sericin, what is silk fiber composed of ?

Silk fiber is primarily composed of two main proteins: fibroin and sericin. These proteins are produced by specialized glands in the silk-producing organisms, such as silkworms (Bombyx mori). The composition of silk fiber can vary depending on factors such as the species of the silk-producing organism and the conditions under which the silk is produced.

Fibroin: Fibroin is the structural protein that forms the core of silk fibers. It constitutes the majority of the silk fiber's mass and is responsible for its strength and resilience. Fibroin is a fibrous protein composed mainly of amino acids such as glycine, alanine, and serine. The exact composition and arrangement of amino acids within fibroin contribute to its unique mechanical properties, including its tensile strength and elasticity.

Sericin: Sericin is a glue-like protein that surrounds and binds the fibroin filaments together within the silk cocoon. It serves to protect the fibroin and provide cohesion to the silk fiber structure. Sericin is composed of various proteins and amino acids, with its composition varying depending on factors such as the silk-producing species. Sericin is typically removed from silk fibers during processing to improve their texture and appearance, leaving behind only the fibroin core.

In addition to proteins, silk fiber may also contain small amounts of other substances such as lipids, sugars, and minerals. These minor components can influence the properties of silk fibers but are present in much smaller quantities compared to fibroin and sericin.

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What are the Various Wild Silk Yarns

Source

1. Reeled Tussar/ Tussar Raw Silk: It is reeled from Tussar cocoons using different appliance. Reeled Tussar is finer in nature.
   
   
2. TussarGicha: Yarn drawn by hand out of Tussar cocoons without any twist.
   
   
3. Tussar Katia: Yarn spun out of Tussar waste after opening and cleaning.
   
   
4. Tussar Jhuri: Yarn spun out of uncleaned Tussar waste without subjecting it to opening and cleaning process.
   
   
5. Balkal yarn: Yarn spun out of Tussar cocoon peduncles, after boiling in alkaline solution and opened up.
   
   
6. Tussar Spun Silk: Yarn spun in the mill out of Tussar silk waste.
   
   
7. Muga Raw Silk: Yarn reeled from Muga cocoons.
   
   
8. Muga Gicha: Yarn drawn by hand out of muga cocoons without any twist.
   
   
9. Hand Spun Endi/ Eri Silk: Yarn spun by hand appliances from Eri cocoons.
   
   
10. Mill Spun Eri Yarn: Yarn spun in the mill from Eri cocoons.

You can find here the various wild silk fabrics and how to take care of silk. 

How Cocoons are measured in Wild Silk ( Vanya Silk)

 Tussar Cocoons:

The unit of measurement of tussar cocoons is Kahan. Number of Cocoons per Kahan vary in different states. In MP one Kahan has 1000 cocoons while in Maharashtra it has 4000 Cocoons. 

About 1200 cocoons are required to produce one kg of yarn. 

ERI

The Eri cocoons are measured on the basis of weight ( kg)

MUGA

The Muga cocoons are transacted in thousand numbers. About 5000 cocoons are required to produce 1 kg of Muga Raw Silk.

Source

What do you Mean by Vanya Silk

 Non mulberry silks such as Tussar, Muga and Eri are called Vanya silks. 

Production Trends ( 2010-11)

Vanya Silk contributed to about 20% of the total raw silk in India.

Eri, Tussar and Muga contributed to about 64%, 33% and 3% of the total Vanya silk

It contributes to about 10% of the total exports of silk goods 

Tussar Silk

Silk Worm : Antheraea mylitta and Antheraea proylei

Feed on: Asan,  Arjun and Oak

India is the second largest producer or Tussar Silk

History: Ram's nuptial gift to Sita included Tussar Silk

Muga Silk

Silk Worm : Antheraea assamensis

Feed on: Som and Sualu

Use of Muga Yarn instead of Zari is finding its support in Indian Weavers

Source

More about Tussar or Tussah or Tassar

Looking for Tussar, I came across several other interesting features. Some of these are as follows:

1. China exports two types of Tussar Silks: 33/37 D Water reeled and 70 D Dry Reeled Silk. I am just wondering if the "China" that is 50/70 quality that we use in India is dry reeled always.

2. There are 7 grades of quality of Tussar Exported by China, 4A, 3A, 2A, A, B, C and Off grade.


3. The standard moisture regain of Tussar Silk is 10% and density is 1.58 to 1.63 gms/cm3.


4. Elongation at break of water reeled tussar is 23% and dry reeled tussar is 16%.


5. China tussar is different from Indian ( Tropical ) tussar due to the fact the China Tussar the species of the worm is different and fed on "Oak Leaves" ( Also done in Himalyan Regions of the country). Whereas in India it is fed on "Arjun" and "Aasan" leaves. 


6. 8 is the usual number of cocoon filaments to form a single thread. The normal size of the thread produced is 30-35 deniers.


7.Tussar silk is the primary kind in the silk which lustrous,bright,soft handfeel,it has highest wear resistance in the natural faric. The Acid & Alkali Resistance of tussah silk is better than mulberry silk.


However I could not find out how they do dry reeling of tussar. Would require your inputs. 


And yes, I found the Tussar process practiced in Bihar, Bhagalpur. You can click here to find out more.

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More about Silkworms and Silk fiber- Mulberry, Muga, Tasar and Eri

Silkworm belong to the order Lepidoptera. They belong to family of Bombycidae and Saturniidae. Under Bomycidae, we have Bombyx Mori or commonly known as Mulberry Silkworm. Under Saturniidae family the eri silk worm is called Philosamia Ricine, Muga is called Anthrerea Assamensis and Tasar is called A. Mylitta. 

Silk filament is made up of 75-80 percent fibroin and 20-25% sericin or gum. Fibroin is insoluble but sericin may be removed by boiling. 

The Muga and Tasar varieties of the worm also secrete a cement which causes a drab color to develop, making bleaching a very laborious process. 

Silk of the B. Mori variety is triangular in cross section. It has a capacity to reflect light and the layers of protein impart it with a pearly sheen. Tasar silk has a flatter structure which is a reason for its dull appearance. 

Muga is rounder and more lustrous. 

The B.Mori and Muga imagos cut their way through one end of the cocoon, thus making the filament discontinuous. The Tasar moth secrets an enzyme called cocoonase, which softens the cocoon shell facilitating  emergence. The eri moth spins an open ended cocoon through which the imago can fly to full term. 

In silk only male worm can fly. 

During the process of boiling of silk 75% of the sericin is removed. Care is taken to retain the 25% of the gum to prevent tangling. If the boiling is insufficient, filaments tend to snap during weaving, while excess boiling increases the amount of waste silk. 

The thread drawn from the cocoon is of uneven consistency, being finer at the beginning and the end. In order to provide uniformity in consistency, additionaly filaments are drawn in course of reeling, the process is called throwing. 

Because of the structure of cocoon, the process of reeling also generates a residue of waste fiber. In B. Mori, about 45% of the product is floss. This material is spun. This is called Matka. In the case of muga worm 25 to 50 percent may be spun. With regard to tasar only about 10 per cent of the filament can be reeled

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What is the difference among Mulberry, Tussar ( Tasar), Muga and ERI Silk

The difference is in the type of worms producing the yarn and the types of leaves they eat.

Mulberry Silk is obtained from BOMBYX MORI feeding on MULBERRY leaves.


Tussar Silk is obtained from ANTHEREA MYLITTA feeding on ARJUN and ASAN leaves.


Muga Silk is obtained from ANTHEREA ASSAMENSIS feeding on SOM and SUALU leaves.

Eri Silk is obtained from CYNTHIA RICINI  feeding on CASTOR OIL leaves.

The eri silk worm is the only completely domesticated silkworm other than Bombyx mori.

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Some Online Resources in Silk

These two websites - one of which is a commercial exporter's and the other is about hand painted silk, provide some valuable information about silk.


First of all, definitions. One can go through the definitions here. However, I was always looking for the definitions of the following types of Silk.

1. Mulberry Silk

I was not particularly looking for this definiton. Silk produced by silk worm (Bombyx Mori) fed on Mulberry Leaves.

2. Tussar Silk

I was particularly looking for this:
Larvae of several species of moth such as Antheraea mylitta, Antheraca proylei, Antherea pernyi and Antheraca yamamai produce this silk.The insects mostly live in the wild on bushes and trees on which they feed.

3. Katiya Silk
A big one for me.

The portion of Tussar cocoons leftover after about 60% reelable silk is spun into Katiya yarn.

4. Balkal Silk

The peduncles (silk that anchors the cocoon, it is very weak) are utilised for production of Balkal yarn.

5. Muga Silk:

It belongs to same family as Tussar. It is popular for its natural golden colour, glossy fine textures and durability. Muga silk is produced by Antheraea assama westwood which is an endemic species prevalent in the Brahmaputra valley and adjoining hills.

Muga silkworm is a polyhageous insect which feeds on leaves of Som, Soalu and other plants which grows abundantly in Brahmapautra valley.

Eri Silk :

The word Eri is a derivative from Sanskrit nomenclature for Castor Plant, eranada. Castor leaf is the main food for the Eri silkworms and so named as Eri. This is the only completely domesticated non-mulberry variety. Its silk is spun as it can not be reeled.

Spun Silk:

A Silk yarn made of short lengths of silk obtained from silk wastes, pierced cocoons or floss which gives yarn its characteristic brilliance. There are two grades of yarn Schappe and Bourette. It is spun on special machinery which in some ways is akin to cotton and worsted.

Noil Silk:

Noil Short fibres removed in combing operation of yarn making of Spun silk is spun into Noil yarn. Noil is mostly produced in Karnataka and Madras.

Dupion Silk:

An irregular, rough silk reeled from double cocoons or cocoons spun side-by-side which are interlocked, making it necessary to reel them together. The unevenness of the yarn confines its use.

Filature Silk


A raw silk which is reeled by machine as distinct from silk prepared by hand in cottage industry.

Matka silk

Another Big One.

Matka Silk is obtained from waste Mulberry silk by hand spinning without removing the gum (sericin). Cocoons required to produce Matka are mainly obtained from Karnataka and Kashmir but spinning is mostly done in the villages of Malda and Murshidabad districts in West Bengal by women by hand spinning.

Filaments of the cocoons of this silk from Bihar were originally unwound and  plied together on a mud pot, or Matka ( Today, they are alikely to be reeled on a woman's thigh)

MASHRU

Though not a silk fabric yet very important from the point of view of traditional textiles. It is a veg based fabric. A satin weave with rayon warp and cotton weft, creates a high glossy surface.

GAJJI

Gajji Silk is satin weave done on silk fabric. Used in Tie-Dye Sarees in Gujarat state of India

Care of Silk Fabric: This site gives it comprehensively among other resources.

such as Interesting Facts about silk Fabrics and Scarf Tying Techniques

I am still looking for the following definitions of Silk

Korean Silk
China Silk
Kora Silk
Desi Silk

Some other Snippets

* All tussar is wild silk which is produced from an unraptured cocoon.

* Ghicha and Matka are produced from Raptured cocoon.

* Korea Silk is also known as 33/37 fiber. Generally we have fabrics of   korea x korea , korea x china and korea x desi. Korea x Korea can be made on powerloom. The other two qualities are not possible to make on powerloom because of their marked evenness.

* When a supplier talks about 2x1 Korea x China, it means he has taken two threads of Korea together in warp (not twisted, but just taken together) .

* Generally reed in these fabrics is always 72

* China silk is also known as 50/70 fiber. It is paler and coarser in appearance than Korea.   

* Desi is a raptured silk from India. Very uneven yet brilliant when worn.