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Silk industry today

Sericulture

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The industry in which farmers raise silkworms (larvae of silkworm-moth) to make cocoons is called “sericultural industry.” Related to this industry, there are also ”silkworm egg producers” who supply silkworm eggs, called Sanshu(Seeds of Silkworms), to silk-raising farmers and “mulberry plant suppliers” who supply young mulberry plants to create mulberry fields.
During the Meiji Period, farmers were able to raise silkworms only once a year in spring under natural conditions, but now they can raise them six times or more a year; in spring, summer, early fall, and late fall (end of fall, early winter).

Life cycle and morphology of silkworms

Silkworms are holometabolous insects which have four growth stages during their lifetime; egg, larva, pupa, and adult. A larva hatched from egg undergoes four moulting cycles in about 25 days and transforms into a Jukusan or a mature larva. It makes a cocoon by emitting filament for 2 to 3 days and transforms into a pupa in another 2 to 3 days, and then emerges as a moth in about 10 days.


  1. Egg laying of silkworm moths
    A silkworm moth lays about 500 silkworm eggs.
  2. Gisan , Kego (Newly hatched larvae)
    Newly hatched larvae, which have not eaten any food yet, are called Gisan(ant worms) or Kego (hairy worms) because they look like ants from their black body hair.
  3. Larva (5th instar)
    The body weight of the 5th-instar larva after has undergone four moults increases by about 10,000 times compared with a newly hatched larvae.
  4. Eiken (Cocooning)
    Silkworm’s spinning to make cocoons is called”cocooning.” They continue to emit a cocoon filament about 1,300-1,500 m long for 2 to 3 days. The thickness of a cocoon filament they emit is about one fourth of a human hair.
  5. Cocoons
    The weight of a cocoon of a silkworm which is raised in present-day is about 2.0 g.

Silk reeling

The industry which makes raw silk from cocoons and sell it is called ”silk-reeling industry.”
The”machine-reeling industry” which purchases good-quality cocoons to make high-quality raw silk used to manufacture raw silk mainly for export from the Meiji Period until the beginning of the Showa Period.
At present, the”Usui raw silk Agricultural Cooperative” organized by silk-raising farmers still runs a silk mill in Gunma Prefecture.

Major processes until raw silk is made from cocoons


  1. Cocoon drying
    Dry the cocoons and kill pupas by heating to keep them for a long time.
  2. Cocoon assorting
    Remove dirty cocoons not appropriate for the reeling of raw silk.
  3. Cocoon boiling
    Boil cocoons to make cocoon filaments easily disentangled.
  4. Reeling
    Twist cocoon filaments disentangled from several cocoons into a strand of raw silk and reel it onto a reel.
  5. Re-reeling
    Re-Reel the raw silk from a reel onto a bigger reel (re-reeling reel).
  6. Bundling
    A bundle of raw silk released from the re-reeling reel is called ”Kase (skein).” About 24 skeins are bundled and packed for shipment.

Textile

Raw silk is a stiff thread with a gluey substance called sericin remaining on the surface. Soft and glossy silk yarns are produced after removing this substance from the surface. This work is called”degumming.” The weaving method of silk textile differs depending on whether it is woven up after degumming or degummed after woven up.


Process of degummed silk fabric (fiber or yarn dyed fabric)

[Raw silk]
Twining
Degumming/Dyeing
(Yarn scouring/dyeing)
Scoured yarn / Colored thread
Weaving
Finish
[Textile]
(plain / woven pattern)

Process of raw silk fabric (piece-dyed fabric)

[Raw silk]
Twining
Weaving
Degumming/Finish [white texture]
(cloth scouring)
Dyeing/Finish
[Textile]
(plain, printed pattern)
Twisted yarn
Threads made by aligning and twisting several filaments of raw silk.
Degummed yarn
Twisted yarn with sericin removed
Weaving
Makes textiles from threads using a weaving machine.
Degummed silk fabric
Textiles woven with threads degummed before woven (scoured yarns) are called ”degummed silk fabric.”

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