How silk is made

One silkworm cocoon is a single unbroken thread, which is reeled off in one piece rather than spun.

stations: 6
things upstream: 6
raw sources: 4
steps from the ground: 3

The short version

Silkworms fed on mulberry leaves spin cocoons from one continuous protein filament held together by a gum called sericin. Producers drop the cocoons in hot water, which dissolves the gum and kills the pupa, then reel the filament off in one length. Several filaments are twisted into thread and woven.

Feed the silkworms

Silkworms eat mulberry leaves until, after the fourth molt, they climb a twig and spin a cocoon. A producer needs about 104 kg of leaves eaten by 3000 worms to get 1 kg of silk.

Goes in
Silk cocoons
Boil the cocoons

Cocoons go into hot or boiling water. It softens the sericin that cements the filaments together, which frees the end of the thread, and it kills the pupa before the moth can chew out and break the filament.

Goes in
Water
Reel off the filament

The loose end is found and the filament is unwound in one continuous length. Silk is not spun like cotton or wool, because it is already a long fiber.
Dry and pack the raw silk

After drying, the raw silk is graded and packed according to quality, ready for the loom.
Twist into thread

Several single filaments are combined and twisted, a step called throwing. The amount and direction of twist decides what kind of yarn comes out, and threads may be plied together.
Weave and dye

Mills weave the thread into fabric and then dye it. Producers in Thailand bleach their yellow silk in tubs of hydrogen peroxide before dyeing.

Goes in
Hydrogen peroxide

End of the lineSilk Next it goes into silk tie, leather gloves.

Worth repeating

About 5000 silkworms are needed to make one pure silk kimono.
The earliest evidence of silk is the protein fibroin in soil from two tombs at Jiahu in Henan, about 8,500 years old.
Silk is about 75 to 80 percent fibroin, coated in 20 to 25 percent sericin.