We were recently asked if the fabric silk could be considered 'Green'. Well, we said that depends to large degree on your definition of green. We tabled a few interpretations of the term and then made some corresponding observations. There are, of course, alternative views, many of which we are sure our readers will feel free to express, as they did when we traversed this terrain earlier in the year. See our mini review of silk after the fold. Renewable
It is renewable resource, as opposed to a finite material, such as fossil fuel derived textiles, like nylon or acrylic. Silk is the protein fibre spun by a silk moth larvae, most commonly Bombyx mori, to make its cocoon. In commercial silk production some moths are retained for breeding so more cocoons can be constructed.
Being a natural fibre, Silk is readily biodegradable after its useful life. It can go on to produce useful mulch or compost, and hence soil, instead of sticking around for the next 500 years, like most petroleum-based fabrics will.
The vast bulk of commercial silk farming (sericulture) occurs in North Asia (China, Korea and Japan), as well as India, so could not be considered a local material to Europe or North America.
Thousands of cocoons are required to produce several metres of silk cloth. Dealing with so many cocoons is labour intensive work. And although silk is often seen as an expensive fibre, its production remains in countries where low wage rates can be exploited. One European company indicates that they "maintain control over the social and medical aspects in our workshops (i.e. working conditions, child labor)". Fair Trade silk products are available, but we unaware of any supply of Certified Fair Trade silk fibre or fabric. Not that means it doesn't exist, of course.
Tussah or Tussur silk, is derived from cocoons collected after the moth has emerged naturally in the field. Unlike cultivated silk, 'wild silk' is a darker, browner colour, reflecting its food source, often oak trees or tannin rich trees. (Sericulture, using leaves of mulberry trees, results in a white silk.) Tussah is more uneven, has small lumps (slubs) and less lustrous (shiny) than cultivated silk. It does however tend to be stronger, probably because it is a somewhat thicker fibre.
In Southern Africa there is another moth, Gonometa rufobrunnea that is also harvested as a wild silk. This moth feeds on leaves of the mopane (aka mopani) tree, as well some acacia. It is not not know what triggers the moth to emerge from the cocoon, so the process can not be industrialised. Cocoons must instead be collected from the ground after the moth has breached the casing and has fallen off the tree. Again a labour intensive operation, not overly conducive to commercialisation. Though good for the moth! Mopani silk is also a fawn colour, like that of Tussah.
A German company, Christoph Fritzsch, suggest they are sourcing their silk from "the first certifiably organic Chinese silkworm."
Cultivated silk needs to be de-gummed of its Sericin content to leave the smooth hand of the raw protein fibre. The gum is removed in a mild alkaline wash. This can result in a 20% reduction the harvested weight of the silk. Some of this lost weight is added in by saturating silk in bath of tin-phosphate-silicate salts. Such 'weighted' silk tends to crush and wrinkle more easily however.
Anna Sova sell 'Eco silk' products. These are said to be processed only with Skal* approved bleaches (no dioxin), use azo free and heavy metal free dyes, and be finished ('sized') with an Indian soap nut, instead of the usual formaldehyde. (*Skal is a well respected Dutch non-profit, that certifies worldwide organic agriculture and production.)
Silk is often quoted as being as strong as steel, for its weight. The problem is that it is used in very fine gauge fibres and thin fabrics. Such lightweight silk fabrics are prone to wear, and are also degraded by exposure to sunlight, as well hot temperatures and the abrasion and twisting that results from laundering.
Obvious not. Because animals excrete the silk from their glands to make the cocoons, and most vegans do not wish to partake of products where animals have been directly involved in the item's production.
Traditional sericulture normally sees the moth chrysalis stifled (steamed), or boiled alive, so they can't escape through the bonds of the cocoon, thus damaging its 300m to 1,000+m of continuous filament, which is usually then 'reeled' or 'spooled' off.
Peace Silk and Ahimsa (non-violence) Silk are commercial processes between sericulture and wild silk. They do allow the mulberry fed moth to leave the cocoon before it is harvested. They are more expensive.
Using 'wild silk' does allow the moth to emerge unharmed, although the resulting much shorter broken threads (about 10-15cm) have to then be 'spun' into yarn. (Yields are obviously lower than cultivated silk, with correspondingly higher prices.)