Material school - Silk

Ever turned a garment inside out and not really understood what type of fabric it is made of?

Within the textile industry, there is a riot of names on fabrics and hard to know what’s what. 

Here we will over time go through the most commonly used fabrics and materials within our industry, the process they go through to become finish products, what qualities they have and the footprint they leave on our planet. 

Second out in our Material school is Silk! To read our first post click here.

What:

Silk is an animal fibre produced by insect larvae, building their cocoons and webs. Although many insects produced silk, only the filament produced by Bombyx Mori, the mulberry silk moth and a few others in the same genus are used in the commercial silk industry.
The discovery of Silk happened in China; with the oldest record of silk production dating back to the middle of the 3rd millennium. Quickly becoming significant in the Chinese economy, with many Chinese dynasties helping to develop the production of silk - finding new techniques in weaving, dyeing and embroidery.

Where:

Most commonly produced in China and India.

How:

Hatching the Eggs

The first stage of silk production is the laying of silkworm eggs, in a controlled environment such as an aluminium box, which is then examined to ensure they are free from disease. The female larva delivers 300 to 400 eggs at any given time.

The eggs of the silkworm moth are incubated until they hatch into larvae.
At this point, the larva is about a quarter of an inch long.

The Feeding Period

Once hatched, the larvae are placed under a fine layer of gauze and fed large amounts of chopped mulberry leaves during which time they shed their skin four times. Larvae fed on mulberry leaves produce the very finest silk. The larva will eat 50,000 times its initial weight in plant material.

The silkworm eats nonstop for roughly six weeks .
After maturing to its maximum size of about 3 inches at around six weeks, it stops eating, changes colour, and is about 10,000 times heavier than when it hatched.

The silkworm will now start to spin a silk cocoon.

Spinning the Cocoon

The silkworm attaches itself to a compartmented frame, twig, tree or shrub in a rearing house to spin a silk cocoon over a three to eight-day period. This period is termed pupating.

Silkworms possess a pair of specially modified salivary glands called sericteries, which are used for the production of fibroin – a clear, viscous, proteinaceous fluid that is forced through openings called spinnerets on the mouthpart of the larva.

Liquid secretions from the two large glands in the insect emerge from the spinneret, a single exit tube in the head. The diameter of the spinneret determines the thickness of the silk thread, which is produced as a long, continuous filament. The secretions harden on exposure to the air and form twin filaments composed of fibroin, a protein material. A second pair of glands secretes a gummy binding fluid called sericin which bonds the two filaments together.

Steadily over the next four days, the silkworm rotates its body in a figure-8 movement some 300,000 times, constructing a cocoon and producing about a kilometre of silk filament.

Reeling the Filament

At this stage, the cocoon is treated with hot air, steam, or boiling water. The silk is then unbound from the cocoon by softening the sericin and then delicately and carefully unwinding, or 'reeling' the filaments from 4 - 8 cocoons at once, sometimes with a slight twist, to create a single strand.

As the sericin protects the silk fibre during processing, this is often left in until the yarn or even woven fabric stage. Raw silk is silk that still contains sericin. Once this is washed out (in soap and boiling water), the fabric is left soft, lustrous, and up to 30% lighter. The amount of usable silk in each cocoon is small, and about 2500 silkworms are required to produce a pound of raw silk.

Benefits:

Silk naturally respells mould and mildew.

Silk is hypoallergenic, and won’t irritate sensitive skin.

Silk fibres are naturally elastic and can stretch up to 20% without breaking.

Silk can absorb up to a third of its weight in water before it feels wet.

 

 

Footprint:

Silk is a highly renewable resource with less impact on the environment that many other fabrics. The silkworms feed on mulberry leaves, which don’t require the use of pesticides or fertilizers to grow.  


Silk for most places is not a local resource, so processing and transportation lead to pollution. Much of the silk in the US and Europe is from China and India. To clean silk, many harsh and intensive treatments and chemicals are used, which can pollute the groundwater. Producing silk uses a very large amount of resources to produce a small amount of silk, some estimate that only thirty-five pounds of silk come from one acre of mulberry trees. The process is also very labour intensive, so it requires many workers.  

 

Source:

Silk Making; How to Make Silk; Silk Production Process. https://texeresilk.com/article/silk_making_how_to_make_silk