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Silk Fiber Facts – Where Does Silk Come From?

Introduction:

Silk is a natural protein fiber, produced by insect larvae to form cocoons. Perhaps the best-known of these larvae are the mulberry silkworm Bombyx mori which are raised in captivity for their silk fiber (sericulture). Commercial silks originate from reared silkworm pupae, which are bred to produce a white-colored silk thread with no mineral on the surface.

Green silkworm on branch

Silkworm - Bombyx mori

Green silkworm on leaf

Silkworm - Bombyx mori on mulberry leaf

Silk fiber is the only natural BCF (Bulk Continuous Fiber), with single fibers often reaching over 9 football fields in length!

Spinning silk from cocoons in water

Spinning silk fiber filaments from the cocoons

The shimmering appearance of silk is due to the triangular prism-like structure of the silk fiber, which allows silk cloth to refract incoming light at different angles, thus producing different colors. Silk has a smooth, soft texture that is not slippery, unlike many synthetic fibers.

Raw silk fiber

An example of raw silk fiber

It’s these unique qualities that are prized by area rug manufacturers. Although 100% silk fiber area rugs do exist, they are very expensive. In my experience silk fiber is more often blended with wool to give rugs a “softer hand” and also to provide interest in the design with its luminescent quality. Because of its expense, Viscose, or artificial silk, is often used as replacement for silk in area rugs.

Cultivation:

silk moth life cycle

Silk Moth Cycle:

Silk moths lay eggs on specially prepared paper. The eggs hatch and the caterpillars (silkworms) are fed fresh mulberry leaves. After about 35 days and 4 moltings, the caterpillars are 10,000 times heavier than when hatched and are ready to begin spinning a cocoon. A straw frame is placed over the tray of caterpillars, and each caterpillar begins spinning a cocoon by moving its head in a pattern.

silkworms foraging on mulberry leaves

Silk Worms Foraging on mulberry leaves

Two glands produce liquid silk and force it through openings in the head called spinnerets. Liquid silk is coated in sericin, a water-soluble protective gum, and solidifies on contact with the air. Within 2–3 days, the caterpillar spins about 1 mile of filament and is completely encased in a cocoon. The silk farmers then heat the cocoons to kill them, leaving some to metamorphose into moths to breed the next generation of caterpillars.

silk worm cocoon

A fully formed cocoon

silk worm cocoon

The beginning of a cocoon - if you look you can just see the the silk worm in the cocoon

Spinning silk from cocoons after boiling

Harvested cocoons after being soaked in boiling water now being spun into silk yarn

Harvested cocoons are then soaked in boiling water to soften the sericin holding the silk fibers together in a cocoon shape. The fibers are then unwound to produce a continuous thread. Since a single thread is too fine and fragile for commercial use, anywhere from three to ten strands are spun together to form a single thread of silk.

this 1:40 minute video gives a brief overview of how silk is made

History:

Silk was first developed in ancient China.

The earliest example of silk has been found in tombs at the neolithic site Jiahu in Henan, and dates back 8,500 years.  Silk fabric from 3630 BC was used as wrapping for the body of a child from a Yangshao culture site in Qingtaicun at Xingyang, Henan.

Although we often think of China together with Silk, India, Thailand and Bangladesh also have a long history of silk cultivation that carries on to present time.