Silk is a natural protein fibre, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture). The shimmering appearance of silk is due to the triangular prism-like structure of the silk fibre, which allows silk cloth to refract incoming light at different angles, thus producing different colors.
Silks are produced by several other insects, but only the silk of moth caterpillars has been used for textile manufacturing. There has been some research into other silks, which differ at the molecular level. Silks are mainly produced by the larvae of insects undergoing complete metamorphosis, but also by some adult insects such as webspinners. Silk production is especially common in the Hymenoptera (bees, wasps, and ants), and is sometimes used in nest construction. Other types of arthropod produce silk, most notably various arachnids such as spiders (spider silk).
A variety of wild silks, produced by caterpillars other than the
mulberry silkworm have been known and used in China, South Asia,
and Europe since ancient times. However, the scale of production
was always far smaller than that of cultivated silks. They differ
from the domesticated varieties in color and texture, and cocoons
gathered in the wild usually have been damaged by the emerging moth
before the cocoons are gathered, so the silk thread that makes up the cocoon
has been torn into shorter lengths. Commercially reared silkworm pupae are
killed by dipping them in boiling water before the adult moths emerge, or by
piercing them with a needle, allowing the whole cocoon to be unraveled as one
continuous thread. This permits a much stronger cloth to be woven from
the silk. Wild silks also tend to be more difficult to dye
than silk from the cultivated silkworm.
Silk fabric was first developed in ancient China, with some of the earliest examples
found as early as 3500 BC. Legend gives credit for developing silk to a Chinese empress,
Lei Zu (Hsi-Ling-Shih, Lei-Tzu). Silks were originally reserved for the Kings of China for their own use
and gifts to others, but spread gradually through Chinese culture and trade both geographically
and socially, and then to many regions of Asia. Silk rapidly became a popular luxury fabric in the
many areas accessible to Chinese merchants because of its texture and luster. Silk was in
great demand, and became a staple of pre-industrial international trade. In July 2007, archeologists
discovered intricately woven and dyed silk textiles in a tomb in Jiangxi province, dated to
the Eastern Zhou Dynasty roughly 2,500 years ago. Although historians have suspected a
long history of a formative textile industry in ancient China, this find of silk textiles
employing “complicated techniques” of weaving and dyeing provides direct
and concrete evidence for silks dating before the Mawangdui-discovery and other
silks dating to the Han Dynasty (202 BC-220 AD).
The first evidence of the silk trade is the finding of silk in the
hair of an Egyptian mummy of the 21st dynasty, c.1070 BC. Ultimately
the silk trade reached as far as the Indian subcontinent,
the Middle East, Europe, and North Africa. This trade
was so extensive that the major set of trade routes
between Europe and Asia has become known as
the Silk Road. The highest development
was in China.
The Emperors of China strove to keep knowledge of sericulture secret to maintain
the Chinese monopoly. Nonetheless sericulture reached Korea around 200 BC, about
the first half of the 1st century AD had reached ancient Khotan, and by AD 300
the practice had been established in India.
Silk is produced, year round, in Thailand by two types of silkworms,
the cultured Bombycidae and wild Saturniidae. Most production
is after the rice harvest in the southern and northeast parts
of the country. Women traditionally weave silk on hand looms,
and pass the skill on to their daughters as weaving is considered
to be a sign of maturity and eligibility for marriage.
Thai silk textiles often use complicated patterns in various
colours and styles. Most regions of Thailand have their own
typical silks. A single thread filament is too thin to use on its
own so women combine many threads to produce a thicker,
usable fibre. They do this by hand-reeling the threads
onto a wooden spindle to produce a uniform strand of
raw silk. The process takes around 40 hours to
produce a half kilogram of Thai silk.
Many local operations use a reeling machine for this task, but some silk threads
are still hand-reeled. The difference is that hand-reeled threads produce three grades of silk: two
fine grades that are ideal for lightweight fabrics, and a thick
grade for heavier material. The silk fabric is soaked in extremely cold water and bleached
before dyeing to remove the natural yellow coloring of Thai silk yarn. To do this, skeins
of silk thread are immersed in large tubs of hydrogen peroxide. Once washed and dried,
the silk is woven on a traditional hand operated loom.[
Silk, known as “Paat” in Eastern India, Pattu in southern parts of India
and Resham in Hindi/Urdu, has a long history in India. Recent
archaeological discoveries in Harappa and Chanhu-daro suggest
that sericulture, employing wild silk threads from native silkworm
species, existed in South Asia during the time of the
Indus Valley Civilization, roughly contemporaneous
with the earliest known silk use in China. Silk is widely
produced today. India is the second largest producer of silk
after China. A majority of the silk in India is produced in Karnataka
State, particularly in Mysore and the North Bangalore regions of
Muddenahalli, Kanivenarayanapura, and Doddaballapur.
India is also the largest consumer of silk in the world. The
tradition of wearing silk sarees in marriages by the brides
is followed in southern parts of India. Silk is worn by people as a symbol
of royalty while attending functions and during festivals. Historically silk
was used by the upper classes, while cotton was used by the poorer classes.
Today silk is mainly produced in Bhoodhan Pochampally (also known as Silk City),
Kanchipuram, Dharmavaram, Mysore, etc. in South India and Banaras in the
North for manufacturing garments and sarees. “Murshidabad silk”, famous from
historical times, is mainly produced in Malda and Murshidabad district of West
Bengal and woven with hand looms in Birbhum
and Murshidabad district.
Another place famous for production of silk is Bhagalpur. The silk from Pochampally
is particularly well-known for its classic designs and enduring quality. The silk is
traditionally hand-woven and hand-dyed and usually also has silver threads woven into
the cloth. Most of this silk is used to make sarees. The sarees usually are very expensive and
vibrant in color. Garments made from silk form an integral part of Indian weddings and other
celebrations. In the northeastern state of Assam, three different types of silk are produced,
collectively called Assam silk: Muga, Eri and Pat silk. Muga, the golden silk, and Eri are
produced by silkworms that are native only to Assam. The heritage of silk rearing
and weaving is very old and continues today especially with the production of Muga and
Pat riha and mekhela chador, the three-piece silk sarees woven with traditional motifs.
Mysore Silk Sarees, which are known for their soft texture,
last many years if carefully maintained.
In the Odyssey, 19.233, when Odysseus, while pretending to be someone
else, is questioned by Penelope about her husband’s clothing, he says
that he wore a shirt “gleaming like the skin of a dried onion” (varies with
translations, literal translation here) which could refer to the
lustrous quality of silk fabric. The Roman Empire knew of and traded
in silk. During the reign of emperor Tiberius, sumptuary laws were passed
that forbade men from wearing silk garments, but these proved ineffectual. Despite the
popularity of silk, the secret of silk-making only reached Europe around AD 550,
via the Byzantine Empire. Legend has it that monks working for the emperor
Justinian I smuggled silkworm eggs to Constantinople in hollow canes from
China. All top-quality looms and weavers were located inside the
Palace complex in Constantinople and the cloth produced was used
in imperial robes or in diplomacy, as gifts to foreign dignitaries.
The remainder was sold at very high prices.
Silk emitted by the silkworm consists of two main proteins, sericin and fibroin, fibroin
being the structural center of the silk, and serecin being the sticky material surrounding it.
Fibroin is made up of the amino acids Gly-Ser-Gly-Ala-Gly-Ala and forms
beta pleated sheets. Hydrogen bonds form between chains, and side chains form above
and below the plane of the hydrogen bond network. The high proportion
(50%) of glycine, which is a small amino acid, allows tight packing and the
fibers are strong and resistant to breaking. The tensile strength is due to the many
interseeded hydrogen bonds, and when stretched the force is applied to these
numerous bonds and they do not break. Silk is resistant to most mineral acids, except
for sulfuric acid, which dissolves it.
It is yellowed by perspiration.
Silk’s absorbency makes it comfortable to wear in warm
weather and while active. Its low conductivity keeps
warm air close to the skin during cold weather. It is often
used for clothing such as shirts, ties, blouses, formal dresses,
high fashion clothes, lingerie, pyjamas, robes, dress suits,
sun dresses and kimonos. Silk’s attractive luster and drape
makes it suitable for many furnishing applications. It is
used for upholstery, wall coverings, window treatments
(if blended with another fiber), rugs, bedding and wall hangings.
While on the decline now, due to artificial fibers, silk has had many industrial
and commercial uses; parachutes, bicycle tires, comforter filling and artillery
gunpowder bags. A special manufacturing process removes the outer
irritant sericin coating of the silk, which makes it suitable as non-absorbable
surgical sutures. This process has also recently led to the
introduction of specialist silk underclothing for children and adults
with eczema where it can significantly
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 “figure 8” pattern. 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 kill most caterpillars by heat, leaving some to
metamorphose into moths to breed the next generation of caterpillars.
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.
As the process of harvesting the silk from the cocoon kills the
larvae, sericulture has been criticized in the early 21st century by
animal rights activists, especially since artificial silks are available.
Mohandas Gandhi was also critical of silk production based on the Ahimsa
philosophy “not to hurt any living thing.” This led to Gandhi’s promotion
of cotton spinning machines, an example of which can be seen at
the Gandhi Institute. He also promoted Ahimsa silk, wild silk
made from the cocoons of wild and semi-wild silk moths.
Ahimsa silk is promoted in parts of Southern India for those
who prefer not to wear silk produced by