Silk: sericulture, properties and uses
Silk is a protein filament spun by the silkworm. Sericulture rears the worms, then cocoons are stifled, reeled, thrown and degummed to give a strong, lustrous yarn.
Draw it: the silkworm life cycle
- back to Egg
For reeled silk the cycle is stopped at the pupa stage.
From cocoon to silk yarn
- 1Rearing (sericulture): eggs are hatched and larvae fed chopped mulberry leaves on trays. The grown larva spins one continuous filament round itself as a cocoon in 2-3 days.
- 2★Stifling: cocoons are heated with steam, hot air or sun to kill the pupa before the moth breaks out and cuts the filament.
- 3Sorting and cooking: good cocoons are picked out and soaked in hot water to soften the sericin gum.
- 4★Reeling: the loose ends of several cocoons are found by brushing and unwound together into one raw-silk thread, held by the softened gum.
- 5Throwing: raw-silk threads are twisted and plied into yarn: organzine (more twist, for warp), tram (less twist, for weft) and crepe (very high twist).
- 6Degumming: boiling in soap solution removes the sericin, so silk becomes soft, white and lustrous and loses about a quarter of its weight. Weighting with metallic salts makes up the weight but makes silk crack with age.
- 7Spun silk: waste from broken or pierced cocoons and the outer floss is cut and spun like cotton into a less lustrous spun silk.
★ one-way, controls the pace
Types of Indian silk
| Silk | Silkworm and food | Features and where |
|---|---|---|
| Mulberry | Bombyx mori; mulberry leaves | Finest, white, most lustrous; most of India's silk; Karnataka (Mysore silk) leads; woven into Kanchipuram, Banarasi and Dharmavaram saris |
| Tasar (tussar) | Antheraea species; arjun, asan and oak leaves | Coarser, golden-brown, textured; Jharkhand and Chhattisgarh; famous weaving at Bhagalpur in Bihar |
| Eri | Samia ricini; castor leaves | Creamy and wool-like; the moth leaves the cocoon, so it is spun, not reeled ('ahimsa silk'); Assam and the north-east |
| Muga | Antheraea assamensis; som and soalu leaves | Natural golden sheen; unique to India, grown mainly in Assam |
Properties of silk
| Property | Silk | So in use |
|---|---|---|
| Structure | Smooth, fine filament; triangular cross-section with rounded corners | Prism-like shape gives a deep lustre |
| Strength | Strongest natural fibre for its fineness; weaker when wet | Fine yet durable; handle gently when wet |
| Elasticity and resiliency | Good elasticity, moderate resiliency | Drapes well; creases less than cotton |
| Absorbency | Good (regain about 11%) | Comfortable; dyes in rich, bright colours |
| Warmth and weight | Light; a poor conductor of heat | Warm in winter, pleasant in summer |
| Chemicals | Harmed by alkalis, chlorine bleach and perspiration | Wash with mild soap or shampoo; never use chlorine bleach |
| Heat and light | Scorches above medium heat; sunlight weakens and yellows it | Iron on the reverse at low heat; dry in shade |
Uses of silk
- Saris and wedding wear: Kanchipuram, Banarasi, Mysore, Dharmavaram, Bhagalpur tussar, Pochampally ikat.
- Dress materials, kurtas, ties, scarves, stoles and lingerie.
- Furnishing: cushion covers, wall hangings, upholstery.
- Medical: silk sutures for stitching wounds.
Silk saris last longer with the right care: wash in cool water with mild soap or shampoo, never use chlorine bleach or washing soda, dry in shade, and sponge off oily food stains and sweat quickly because both weaken silk.
2 marks: “What is sericulture?” The rearing of silkworms on mulberry or other leaves to produce cocoons for raw silk.
5 marks: “Write a short note on the non-mulberry (wild) silks of India.” Tasar (Antheraea; arjun and asan; Jharkhand; Bhagalpur weaving), eri (castor; spun 'ahimsa' silk), muga (golden; mainly Assam); compare with mulberry.
10 marks: “Explain the manufacture of silk from sericulture to yarn. Add its properties and uses.” Life-cycle diagram; rearing, stifling, reeling, throwing, degumming, spun silk; properties table; uses.
Silk steps: R-S-R-T-D, 'Rani Saw Red Threads Drying': Rear, Stifle, Reel, Throw, Degum.