Silk Weaving for British Airways 1
Silk Weaving for British Airways 2
Silk Weaving for British Airways 3
Silk Weaving for British Airways 4
Silk Weaving for British Airways 5
Silk Weaving for British Airways 6
Sericulture from the Egg to the Cocoon
During the production of silk the most labour intensive period is that of rearing the silk worm, also known as sericulture. The most common moth used is the Bombyx mori which is raised domestically; it no longer survives in the wild.
Silk worms are scientifically caterpillars
There are over 500 species of silk worms that look after themselves in the wild. They live off oak and other leaves. When they are moths, they are bigger and more robust than Bombyx mori which leads to tougher and rougher silk. This silk is not as easy to bleach and dye as the silk produced from mulberry leaves.
The second largest source of silk after the Bombyx mori is the Tussah silk moth, Antheraea mylitta, from India. This moth is a lot bigger than the Bombix mori with a wingspan of 15cm. The cocoons produced are at least twice as big as the Bombix mori and normally grey to brown in colour. This silk is known as Tussah, Tusser, Tusar, Tusseh, and Tuser. It is very durable, coarse and the silk is dark-coloured. It is very popular in India.
The Tussah silk moth cannot be domesticated and is bred in the jungles of Bengal and other places in India where they eat a variety of plants. They can migrate vast distances
One male Tussah is recorded as migrating 100 miles.
Silk worms go through four stages during their life cycle, commonly called egg, caterpillar, chrysalis and adult/moth. Scientifically, these stages are known as ova, larva, pupa and imago.
The Life Cycle of a Silk Worm
The eggs need a spell of cold weather to trigger their development and can hatch between six weeks and 12 months after they were deposited. Traditionally, the eggs were brought out of cold storage during the first week of spring as the mulberry trees begin to bud. Healthy eggs are bluish/grey, eggs that are black or yellow will never hatch. The sex of the moth is determined from the time the eggs are fertilized, however visible signs are hard to see in the caterpillar. They are more apparent in the cocoon and very clear in the moth. Within a week the tiny insects around 1 to 2 mm long hatch. Their one desire in life is to eat so they breathe through nine holes down each side of their body so that it does not interfere with their eating. The breathing holes are called spiracles.These worms are just hatching from eggs that are the size of a pin head. This picture is larger than life.
Cultivated silk worms increase their body weight 10,000 times during their 25 – 28 day life cycle.
This fully grown silkworm is surrounded by newly hatched silkworms. The fully grown worm is 8,000 times heavier and 23 times larger than the newborn worms. This picture is larger than life.
To produce 1 pound of raw silk 2 cwt of mulberry leaves is required.
Occasionally the worm will sleep for around a day then it wakes, wriggles out of its skin including its jaw and carry on eating. The worms moult around four times and sometimes eat their own skin; the scientific term for the shedding of the skin is ecdysis. Each stage of a caterpillar’s life is called an instar and there are five stages between egg and chrysalis. Within five weeks they have grown from 1 mm to 70/80mm. It is commonly believed that the worm will only eat white mulberry (morus alba) leaves to produce silk, however an artificial diet consisting of mulberry leaves, Soya beans and cornstarch has proved successful. The worms in the museum are being successfully fed on artificial food and cabbage leaves. Worms will also eat black mulberry (morus nigra) and cabbage but this can cause slow development, higher mortality and lighter cocoons. The food should not be warm as this kills the worms. As early as 1609 William Stallenge noted that silk worms should be fed on leaves of their own age.Silk worms feeding on mulberry leaves
A fully grown caterpillar is a menacing sight: it is grey with a retractable head and when disturbed the head and first few segments of the body swell up. They have eight pairs of legs: three pairs are ‘true legs’ which are destined to become the legs of the adult moth;four pairs of ‘prolegs’ towards the front of the middle of the body; one pair of claspers at the end of the body to help them remain attached to the food source.
This worm has become glossy and transparent because its silk glands are full so it is ready to spin a cocoon.
After they moult for the final time, the worms become fidgety and restless as they look for a place to start building their cocoon. Initially they build a light safety web which they build into the full cocoon. To build the cocoon the worm excretes a semi liquid mixture in a figure of eight from two pairs of spinnerets which are the openings of the tube which leads from the two silk glands that run the length of their body. The glands within the worm’s body are 38.1cm (15 inches) long. The semi liquid mixture is protein covered in gummy sericin which is produced at around 30 cm (one foot) per minute. When inside the worm the mixture is liquid but once it is exposed to air the mixture turns to fibre and becomes waterproof.It takes the worms two to three days to complete its cocoon and it needs to move its head from side to side around 150,000 times. Inside the cocoon the caterpillar is transforming into a moth.
Cocoons at different stages of completion.
The average length of the silk from a single cocoon it 300-400 meters.
After around two weeks the moth emerges by spitting out an enzyme which weakens the cocoon.
The newly emerged moth waits for its wings to dry.
When the moths emerge the female always has a large abdomen which is full of eggs and larger wings so it is easy to separate from the male. The male moth has a pair of feathery feelers (antennae) which are vital for detecting the female scent particularly in the wild.Once they have emerged, the moths are solely interested in mating, so the female produces a large amount of scent and within several hours she lays between 300 and 500 eggs. When a male moth is excited by a female, its wings often vibrate which will cause him to rub most of the scales off his wings and those of his mate. However this movement of the wings is not related to flying, it is because of an increase in the metabolic rate of the body. The moths die within two or three days. They have undeveloped mouth parts and are incapable of flight; however this is not because of the design of their wings, it is because the muscle are no longer developed as a result of generations of lack of use. The eggs are pale when first deposited but turn to slate blue soon afterwards.
Male and female cocoons are sorted by weight, the female cocoons are heavier. Some cocoons are kept to continue the breeding stock, often refered to as ‘queen cocoons’ whatever their sex. The majority are taken and the chrysalis is killed by being baked in the oven or steam to prevent it emerging and damaging the silk with the enzymes. These cocoons are put in hot mater to melt the sericin and brushed gently in order to find the end of the filament which will stick to the brush. Once the short and loose exterior filaments are removed the single continuous filament is ready to be unwound. A single cocoon is too fine for practical use so 5 to 7 cocoons are unwound together. As the filaments leaves the water the sericin dries and hardens so binding the individual filaments together. This process is known as reeling.
Brushing the cocoons to find the ends.
The manner in which the silk worms are reared determines the quantity and quality of the silk. The worms are still regarded as fragile creatures.
Ancient Chinese guidelines are still observed in China today: Barking dogs, crowing cocks, foul smell can upset freshly hatched worms; larvae should rest on dry mattresses; worms must eat, sleep and work in harmony and any out of sync worms must be buried or fed to the fish to avoid variations in the silk; drowsy, newly hatched worms need tickling with a chicken feather to encourage development; attendant/silkworm mothers should have no bad smells, wear clean simple cloth so as not to stir up the air, and not eat or touch chicory.
Commercial production of silk relies upon three modern advancements: fooling
he silkworms into believing it is perpetually summer; artificial diets; providing a continuous supply of food.The farms use several different methods to raise the silk worms. Some cover trays in mulberry leaves, as shown in the picture, and then provide cardboard squares for the worms to spin their cocoon in. Other farms provide straw for the worms to spin their cocoon in.
It takes approximately 110 cocoons to make a silk tie
It takes approximately 630 cocoons to make a silk blouse
Heavy silk kimonos need 3,000 silkworms eating 135 pounds of mulberry leaves
8,000 worms will make 10 silk blouses and eat 350 pounds of mulberry leaves
An average cocoon contains 300-400 meters of silk
Female cocoons are heavier than male cocoons
© 2002 Macclesfield Museums Trust. Registered Charity No. 519521 © 2002 The Heritage Centre.