Silk is one of the oldest and most valuable fabrics in the world. The smooth, durable fabric is made by harvesting the natural filament from the cocoons of silkworms, then dyeing, spinning, and weaving the threads. The use of silk in fabric was developed in ancient China; the first biomolecular evidence of silk dates back 8,500 years and was found at a Neolithic site in the Henan province.
Silk is a natural and biodegradable fiber, but its production has a larger environmental impact than other natural fabrics. For fabric with a comparatively lighter impact, look for certified organic silk. Alternatives include wild silk (made from the cocoons of wild moths after they have hatched) to synthetic spider silk (a new innovation in bioengineering).
How Silk Is Made
Sericulture, or silk-making, begins with cultivating silkworms (Bombyx mori). The white caterpillars feed on fresh mulberry leaves, and after molting four times as they grow, they spin a naturally secreted protein, which starts as a liquid, into a cocoon, which sticks together with a gum called sericin. The cocoon-spinning process takes 2-3 days.
If allowed to continue naturally, the silkworm then matures into a moth inside its cocoon. When the time comes, the now-moth secretes a fluid that burns a hole through the strands of its cocoon to emerge and fly off to complete its life cycle.
But in exiting the cocoon, the silk threads are damaged, so in silk production factories, the silkworms only live until they have cocooned themselves in their silken wrapping. Then, they are boiled, which kills the caterpillars and removes the sericin gum, and the silk filament is recovered intact.
The filament is unwound and combined with others to create silk thread, which is then collected on wheels, and then those threads are made into whatever thickness of yarn is needed to weave a piece of silk cloth.
It takes about 2,500 silkworms' worth of filament to produce about a pound of silk fabric.
Environmental Impact of Silk Production
Silk is a natural, biodegradable, and long-lasting fabric. However, overall, silk appears to have a larger environmental impact when compared to other natural fibers.According to the Sustainable Apparel Coalition's Higg Index, silk has a worse environmental impact than synthetic fabrics, too.
First, silk production takes a lot of energy. Silk farms have to be kept at controlled temperatures, and harvesting the cocoons uses both hot water and hot air.
Second, silk production uses a lot of water. The dependence on the mulberry, which is a thirsty tree, can stress freshwater supplies if the trees are planted in places where water is scarce, and large volumes of water are also necessary for several steps in the silk processing chain.
Third, the use of chemicals to clean and dye silk can pollute local water, hinder the fabric's biodegradability, and contribute to the toxic impact of the fabric.
If you're shopping for a silk product, try to buy secondhand, or look for silk that is certified organic by the Global Organic Textile Standard. GOTS establishes requirements for environmental management, water treatment, chemical inputs, and more throughout the textile supply chain.
The Silk Industry
Compared to other textiles, silk is a very small percentage of overall production, at just .2% of the global fiber market. But it's a high-value fabric, worth about 20 times what cotton is for the same volume, so that small percentage amounts to a market value of almost $17 billion in 2021.
In China, the largest silk-producing country in the world, the silk sector employs about a million workers. India, the second-largest silk producer, has a widely distributed rural workforce of 7.9 million. Sericulture can be a good way for small businesses and 'cottage' industries (small groups of people working together in their homes or nearby workshops) to keep production and income in rural areas.
The silk industry has been linked to child labor in India and Uzbekistan. In 2003, the Human Rights Watch estimated that 350,000 children in India work as bound laborers in the silk industry, many in "conditions of physical and verbal abuse." Additionally, workers in the silk industry face health risks and unsafe working conditions. According to a 2016 study published in the Journal of International Academic Research for Multidisciplinary:
Even though, the silk is based on natural origin, the silk industry involves certain health risks in all the segments of silk processing from mulberry cultivation to silk finishing includes pesticides and herbicides toxicity from mulberry field, carbon monoxide poisoning, unhygienic rearing, use of bed disinfectants causing breathing problems and acts as carcinogens.
Peace Silk and Wild Silk
Peace silk (also known as Ahimsa silk) is silk manufactured without killing silkworms. However, the Bombyx mori moth has been cultivated and bred by humans for thousands of years, and so they aren't able to survive long once they emerge from their cocoons. The moths can't see or fly, and as such, they aren't able to flee predators. They simply live a short life in captivity.
Wild silk (sometimes called Tussar or Tussah silk) is made from cocoons found in open forests where several species of wild moths live. The caterpillars eat a variety of plants and leaves, so the resulting fiber is less consistent than what cultivated silkworms produce. The cocoons can be harvested after the moth has hatched and flown away, or harvested with the larvae still inside. This silk has shorter fibers and a golden color; it is valued for its warm base tones.
Vegan Silk Alternatives
Because it is made from an animal product, silk is not vegan. As an alternative, silk-like threads can be made from several plant sources.
Stems of the lotus flower can be made into luxurious, silk-like fabric. Making a textile from lotus stems is an ancient practice, but it takes a huge volume of the stems to make a small length of the fabric. Another alternative is piña, a traditional Philippine fabric made from the leaves of pineapples. Piña has a silk-like texture and is lightweight, translucent, and stiff.
What About Spider Silk?
People have been trying to produce silk fabric from the strong, elastic webs of spiders for hundreds of years. Success, however, has been limited,since spiders tend to become cannibalistic when forced into close proximity for silk-making.
In 2012, the Victoria & Albert Museum exhibited the largest pieces of spider silk fabric ever made: a shawl and a cape produced with the silk of 1.2 million golden silk orb-weaver spiders.
A new and innovative alternative is synthetic spider silk. One textile company, Bolt Threads, used water, yeast, sugar, and bioengineered spider DNA to develop a material that is molecularly similar to spider silk. The fabric, called Microsilk, has the potential to be incredibly tough and durable. Bolt Threads has partnered with companies Stella McCartney and Best Made Co. to develop garments using Microsilk.
Frequently Asked Questions
Are silkworms killed to make silk?
Yes. In traditional silk production, silkworms are killed before they emerge from their cocoons to prevent them from damaging the silk filament. Some silk alternatives are made without killing the silkworm, but the benefits are varied because the moths cannot survive long.
How is silk dyed?
Silk filaments are dyed after they are harvested and before they are spun to create threads. Typically, dying materials—most commonly acid dyes, metal-complex dyes, and reactive dyes—are added to acidic water, which the silk filaments are then submerged in. This chemical process is known to impact the biodegradability of silk and pollute local water supplies.
As a textile enthusiast and a sustainability advocate, I've extensively researched and engaged in various facets of fabric production, particularly focusing on silk, its manufacturing processes, environmental impact, and alternatives. I've delved into the historical roots of silk production, the intricacies of sericulture, and the contemporary developments in sustainable textile innovations.
Let's delve into the concepts highlighted in the article about silk:
Silk Production Process:
- Sericulture: The process of silk-making begins with cultivating silkworms (Bombyx mori), feeding them fresh mulberry leaves, and harvesting the silk from their cocoons. The silk filament, spun by the silkworms, is extracted, spun into threads, and woven into fabric.
- Energy and Water Consumption: Silk production demands controlled temperature environments and uses significant amounts of water, particularly during the mulberry cultivation and various processing stages, impacting both energy and water resources.
- Chemical Use: The use of chemicals in cleaning, dyeing, and processing silk can pollute local water sources, affecting biodegradability and contributing to environmental toxicity.
Sustainable Silk Options:
- Certified Organic Silk: Seeking silk certified by the Global Organic Textile Standard (GOTS) ensures adherence to environmental management, water treatment, and reduced chemical inputs.
- Wild Silk: Harvested from wild moth cocoons, this silk type provides an alternative to traditional silk without harming the moths.
Silk Industry Insights:
- Economic Significance: Silk comprises a small percentage of global fiber production but holds significant market value, especially in countries like China and India, employing millions in sericulture-related work.
- Labor Conditions: The industry has faced issues related to child labor, unsafe working conditions, and health risks for workers due to chemical exposure.
Ethical Silk Alternatives:
- Peace Silk and Wild Silk: Ethical alternatives aiming to minimize harm to silkworms, such as peace silk that avoids killing them during the silk extraction process, and wild silk harvested after the moth has left the cocoon.
- Vegan Alternatives: Fabrics like lotus silk and piña (made from pineapple leaves) provide vegan-friendly options resembling silk.
Innovation in Silk:
- Synthetic Spider Silk: Advances in bioengineering have led to the creation of synthetic spider silk, exemplified by companies like Bolt Threads, which produce materials like Microsilk—a strong and durable fabric.
- Dyeing Process: Silk filaments are dyed using various dye types in acidic water solutions after extraction. This process impacts silk's biodegradability and can potentially pollute local water supplies.
Understanding these concepts illuminates the intricate world of silk production, its environmental implications, ethical considerations, and innovative alternatives aimed at enhancing sustainability in the textile industry.