Etymology
Let’s start with the term: mulberry is a common name for a morus tree. Morus leaves feed precious insects called bombyx mori (morus - mori), widely known as silkworms, the major source of silk fiber, also known as cultivated silk or mulberry silk.
This Bombyx Mori the Silkworm is a plain and unpretentious little critter, a large pale moth with 4-6cm wing spread. It was tamed and domesticated in ancient China 5000 year ago.
After mating a female moths lays 500-700 eggs, and larvae, hatching from these eggs, prefer to be called caterpillars. It takes them about a month to grow and gain courage, and then they dive into the transformation process: they are ready to become pupae, so they start weaving cocoons.
Just before weaving the silkworms finally stop eating mulberry leaves (something they did permanently all life since hatching), only because silk glands in their mouths overflow with sticky liquid. This liquid hardens in contact with air, so the thin thread trails behind the caterpillar wherever it goes. It’s time to find a comfortable stick and get to work. The insect spins its head for 3-4 days to cover itself with endless layers of the finest silk filament, the oval cocoon, up to 6cm long.
Each cocoon is 300-900 meter of one continuous silk fiber. The cocoons enter the final stage: they are boiled in hot water or heated by steam, and the pupae inside get killed, never to become moths. And this is why this common method of silk production is believed by many to be unhumane.
However, international textile industry doesn’t have a replacement both for this archaic technology and for this unique thread.
History
According to Confucius and the legends of China, once upon a time (2-3 thousand years before Chirst) a 14-year old Hsi Ling Shih, empress of China, was having her tea under a mulberry tree when suddenly a cocoon fell off the tree right into her hot tea. She tried to take out the cocoon and found herself pulling a finest thread imaginable, and decided to weave a fabric of it… so the technology was born.
Following advice of her husband, the legendary Yellow Emperor of China, Hsi Ling Shih took time to study the habits of silkworms, perfect the process and instruct people the art of sericulture. Later generations titled her the Goddess of Silk.
There are even more legends about how the heavily guarded secret of silk production left China to spread around the world. The one repeated most often is that silkworm eggs, mulberry seeds and knowledge was smuggled out of the country by a chinese princess who married into the Khotan kingdom. The princess became convinced, for whatever reasons, that she would be better off in her new country with the secret of silk than without it, and no laws could stop her.
Fiber properties and production process
One kilogram of silk fiber is produced by joint workforce of 5-6 thousand silkworms. Handling the insects, collecting the raw fiber, as well as further fabric production is labour- and time-consuming, therefore the high cost of the fabric.
Cocoon silk is roughly 3/4 fibroin (fiber) and 1/4 sericin (cocoon glue). Through the microscope you will see of two parallel fibroin filaments with lumps of sericin stuck to them. There is also a small amount of wax, fat and minerals. The fiber is 32 mkm thin (8 times smaller than 1 pixel), and it can sometimes be up to 1.5 kilometers. Mulberry silk is usually white with pearl shimmer.
As we already mentioned, as the first step of production the cocoons are brought together, heated by steam to kill the pupae, and then kept in 87-94C water to soften the gum the holds the cocoon fiber together. During this stage part of the sticky sericin is washed out, and now the cocoon can be carefully unwound.
The long cocoon fibers are now spun together into the so called strand silk or grege silk. A good thread is made of 5-8-12 fibers. As soon as one fiber ends, another is attached to the strand in its place to get a very long continous thread of raw silk. Skeins or reels of raw silk pass on to the next production stage.
Preparation to dyeing
The long thread of raw silk is rough and it has no shimmer, because it is protected by sericin layer. Sericin is usually not removed until the yarn is ready for dyeing. Sometimes they even weave the fabric to completion without degumming it, to avoid abrasion of the thread in the loom, and only then wash and dye the fabric.
Sericin is dissolved in water, alkali and acids. The solution used for degumming should be neutral to fibroin, the main component of the silk fiber, which is quite sensitive to acids and alkali.
During the degumming process silk loses 15-25% of its weight, and acquires its famous texture, softness and sheen. (via: http://www.wormspit.com/degumming.htm)
Properties of baby wraps with mulberry silk
By the way, the reason why the fabric becomes so shiny is that silk thread has a triangular cross section and, like a prism, refracts the light, which causes such a beautiful color and gloss transfusion. Silk fabric is therefore nice on the touch, sleek, shiny and draping.
- Silk slings require delicate handling: hand wash and low temperature (not higher than 140-165C) ironing
- Silk yarn easily frays and becomes fluffy. Pulls and snags are one of the common problems with natural silk babywraps
- Silk is very absorbent, it can take in up to 30% of its weight without feeling wet, and it doesn’t take long to dry. It’s an important advantage of silk wraps both for mother and the baby she wears
- Silk cloth has unique thermal quality: it doesn’t conduct heat and feels cool in hot weather and warms you when it’s cold
- If handled and worn carefully, silk fabrics are very durable
- Silk fabric is weakened by long exposure to sunlight, that’s why it’s a bad idea to dry them in the sun or leave them in the open, when you are on the beach
- Smell. Silk, just as wool, has its own distinctive smell. Mulberry silk is the least smelling of all silk types: it either has no smell at all, or has slight smell that increases when the fabric is wet. This is the result of production technology. The source of silk smell is sericin, and mulberry silk is washed several times during production to get rid of most or all of this substance.
- Don’t forget to wash your silk wrap, especially when you are putting it away for a while. Otherwise it may get yellow stains
If you are not a textile professional:
Note that mulberry silk, also known as cultivated silk, is the fabric we think about when we talk about “silk”, meaning soft, light, sleek and streaming fabric.
There are other types of silk, and their properties are very different from mulberry silk!
Sources:
Wikipedia: History of silk, Silk, Silk Road
Wikiznanie Silk (in russian)
Michael Cook’s site http://www.wormspit.com/ first-hand information about homemade silk production. He also has curious files like “Letters from the Secretary of the Treasury in Relation to the Growth and Manufacture of Silk, Gales and Season, 1828”, as well as links to silk producers and silkworm rearing.
https://randomwire.com/silk-production-in-wuzhen/
Blog about silk embroidery art - An Introduction to Silk Cultivation (Sericulture)
Blog Jennifer's Hamam who helps to support a weaving tradition in Turkey http://jennifershamam.blogspot.ru/
Silk production in Wuzhen (China) https://randomwire.com/silk-production-in-wuzhen
Excursion to the Silk Farm in Dalat (Vietnam) in photos
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Silk Production in Wuzhen (China)
