By Michael Cook

A Bombyx silkmoth surrounded by different types of cocoons. Clockwise from top: four strains of Bombyx, dupion (double) Bombyx cocoons, Tensan, Eri, Oak Tussah, Polyphemus, and Cecropia.

Silk is a protein fiber, secreted from a special gland in the chin of a caterpillar. In the wild, caterpillars use the silk to build snug cocoons to protect them while they change into pupae and then into adult moths.

Bombyx mori, the domesticated silkmoth, is the world's only truly domesticated insect. The larvae are so dependent on human care that they will starve to death if not hand-fed. They do not exist, and never existed, in the wild; they were bred up from wild species, like house cats and sweet corn.

Here's the story according to Confucius: About 2800 B.C.E., the Empress Xi-Ling-Shi, wife of the Yellow Emperor, was having tea in her garden one afternoon. As she sat there, a white cocoon fell from the mulberry tree into her steaming teacup. When she fished it out with her chopsticks, it unwound into soft, strong, shiny threads, and the clever Empress realized that it could be fashioned into thread for weaving.

Whether the actual discovery occurred over tea or not, the Chinese managed to keep silk a secret for many centuries. Silk could be sold or traded, but the secret of its production was jealously guarded, and anyone caught trying to smuggle the silkworms and the knowledge of their cultivation out of China was executed. It eventually spread to Korea and Japan, and then to India, and finally to Europe during the late middle ages, hidden in the headdresses of princesses and the hollow walking staffs of monks. Silk centers became established in many parts of Europe, including Greece, Italy, France, and even England. With the exploration of the New World, it spread to regions of North and South America.

The stages in the life cycle of the domestic silk moth.
From eggs to cocoons takes about four to five weeks.

The domestic silkmoth takes about six to eight weeks to complete one round of its life cycle. Eggs are stored by refrigeration between cycles; if you do this at home, the door of the refrigerator stays around the right temperature. After they are taken out of cold storage, it's a week to two weeks before they hatch. Once hatched, they will eat mulberry leaves for approximately four weeks until they spin their cocoons. The caterpillars, or silkworms, will change their skins four times, making five stages called instars. The final instar caterpillars are huge; they are often as thick and long as an adult's pinkie finger. They spin their cocoons for about three days, and then spend two to three weeks inside the cocoons before emerging as moths. The moths use a special enzyme to help dissolve the silk on one end of the cocoon, and crawl out.

The moths are entirely flightless. The females release a special pheromone that attracts the males, who come running to mate with them. They stay joined up for several hours to a day, and then they separate and the female starts laying the 200-500 mustard-seed-sized eggs. The moths do not have mouths, and cannot eat or drink, so they die once their stores of energy and moisture are used up. This is not a result of breeding; it's just the way silkmoths are. Their entire life cycle, from eggs to eggs, takes about six to eight weeks.

One of the wonders of Bombyx cocoons, is that they are spun by the caterpillar in a single unbroken strand. This strand usually ranges between 600 and 1500 meters in length; 1500 meters is nearly a mile. Most cocoon filaments aren't that long -- that's like a Grand Champion cocoon -- but they definitely do exist. The strand is called a bave; it is made of two tiny sub-strands called brins. The brins are made of a protein called fibroin, which is joined together by another protein called sericin, or silk gum. The sericin makes the cocoon shell tough and hard like paper, and is often useful in silk processing to keep the thread from shredding. Because they are made in single strands, the cocoons can actually be unwound, a process called reeling. In order to reel the cocoons, the pupa inside must be stifled, or killed, with heat so that it does not emerge and break a hole in that long fiber. Stifling is an issue for many strict vegetarians and vegans, who won't wear or work with this kind of silk because the bugs die in the process.

Spools of organzine and tram.

The individual bave is very fine, about two and a quarter million yards per pound. At this weight, it's too fine to be useful by itself, so the baves from multiple cocoons, from 6 to 100 depending on the end use, are reeled together. In order to unwind the cocoons, they are soaked in hot water, and the ends are located with a brush.

Reeling makes a fine, shiny fiber referred to as raw silk filament. The multiple baves in the filament are joined together by the sericin, which is softened but not dissolved by the hot water, so that raw silk looks like a single thread.

Raw silk can be made into a variety of beautiful and useful yarns; of these, only a few are of interest to the hand-spinner and knitter. Organzine is a two-or-more ply yarn which is made by twisting the raw silk filaments one direction and then plying them back the other direction; it is strong and fairly shiny. Most of the fine knitting silks are organzine yarns. Tram is made by twisting the fibers more gently in only one direction to make a soft singles yarn; tram is more often used for weaving weft, and for embroidery where it does not need to bear a lot of stress. Tram is the most shiny of silk yarns, but doesn't handle tension or abrasion as well as organzine. Tram and organzine yarns may be useful to you as a binder thread when spinning specialty yarns, or can be plied up with other fibers to add shine and color. Because they are not drafted from short fibers, these yarns are called reeled or "thrown" silks. Throwing refers to the twisting process; it is done in industry by special machines, but it can also be done at home using a spindle or a wheel. The general rule of thumb is that more twist means more strength, but less shine. Softly twisted silks sometimes pill or snag easily. Tightly twisted silks can be hard or harsh in the hand; many spinners remark on this with the sari silk waste yarns, which are made from the off-cuts of silk weaving looms. A lot of silk fabrics are made using organzine for the warp and tram for the weft; this produces a strong fabric but with a high sheen.

The next step for most silks is degumming. Degumming is a simmering process using an alkaline surfactant bath that removes the sericin, leaving the silk soft and shiny. Some commercial silk processors use an enzyme to assist with this, but others don't. Just like scouring the lanolin out of wool, degumming can be a progressive process -- you can partially, mostly, or fully degum silk. Most reeled silks are degummed in the yarn stage, before dyeing. Others are left raw, with the gum in. Certain fabrics are degummed after weaving, because the gum protects the thread from abrasion on the loom, but some are left raw, like silk organza. The gum gives the silk a stiff hand, which can be useful in certain situations, especially when the fabric should be sheer but fairly stiff.

A note about the term "raw silk" -- raw silk is like raw food -- it hasn't been cooked (degummed). Lots of people refer to a yarn or fabric as "raw silk" when what they really mean is one of three totally different things: spun silk (which is almost always degummed), silk noil (which is, again, almost always degummed) or dupioni silk, which is usually degummed. Dupioni silk is made by hand-reeling cocoons where two silkworms have spun one joint-effort cocoon; it has characteristic lumps and slubs, but a lot of sheen.

Mix the solution up [see recipe at right]. You can use a gallon water jug, and just pour in the chemicals and fill it up with water. The solution does not go bad, but it will settle, so shake before using. Fill a crafts-only kettle with enough solution to float whatever you're degumming, and bring the solution to a boil. Turn it down so that it stays hot, but does NOT bubble any more. Introduce the yarn, waste, cocoons, or whatever you're degumming, and let it simmer for 30 to 45 minutes, gently moving the fiber or yarn a couple of times, but never stirring. Make sure the kettle stays hot but does not boil. Silk will not felt or full, although the yarn may bloom somewhat. Cocoons and other loose fiber can, however, mat up if stirred or boiled. For skeins of yarn, it helps if you use a stick or a stainless spoon to lower the skein into the kettle, and leave the stick/spoon in the kettle with the skein on it. It makes it easier to pull it out again, and keeps the skein from tangling. Most spun silk yarns and fibers won't need degumming; they are typically degummed before the spinning process.

Silk fibers naturally want to be in a slightly acid situation. After dyeing, washing, or especially degumming, it is important to re-acidify the silk with a mild acid. I usually prefer citric acid, because it is cheap and doesn't smell; use about a tablespoon per a gallon or so of water as a rinse. Vinegar also works; use a quarter-cup "glug" or so per gallon of water. Silk has a special characteristic called "scroop" -- this is often referred to as a crunchy feel, and it also has a rustly sound. Scroop is like the feeling of squeezing a big bag of cornstarch or powdered sugar, or stepping down into very powdery snow. Acid helps restore the scroop to silk, as well as keeping it happy and in good shape. Silks which are dyed with alkaline dyes or stored in alkaline conditions for too long can shatter -- you go to pick up a piece of silk fabric, and it comes up in dozens of tiny bits. I got to see this when I worked for a history museum, in some beautiful old dresses. Unfortunately, shattered silk is almost impossible to repair, because there's no strength to it any more.

Different forms of silk fiber. From left: Cocoon strippings, reeler's waste, throwster's waste,
silk hanky, degummed cocoons, carded Polyphemus silk batt (with Bellwether silk spindle),
combed Eri silk top. All fibers are from the author's silkworms.

The vast majority of the silk used by hand spinners is waste from the reeling process. Cocoons that are cut open for breeding, those that are stained or faulty, and all sorts of different snagged or cut bits get turned into spinning fiber and spun yarns. There are dozens of different machines that handle the reeled silk during the various winding and twisting processes; each one of them produces a distinct variety of waste. Some of the longer, better-quality waste fibers are degummed, carded, and then combed to make silk sliver or top; these make the shiniest and most expensive spun silk yarns. Most of the silk that you can buy for hand spinning is this sliver/top form. In terms of spinning, it is handled much like wool or alpaca, although the silk lacks scales, and can be more slippery and may need a firmer grip. It is often easier and faster to spin silk from the fold; pull on the end of the top, removing a little bundle of fibers, and fold it over the fingertip.

Silk bricks are a preparation that is made after the silk is combed into a rectangle, but before it is made into tops; they are folded tightly and compacted into a little tight rectangle, thus the name. Cocoons that are used for breeding are typically cut open on one end to remove the pupa, so that the moths don't pee on the cocoons (lovely, but true) -- these can be degummed, and then turned into hankies or caps or left as degummed cocoons, which look like compacted cotton balls. The cut cocoons are also used without degumming to make decorative accents and jewelry. Hankies, also called mawatas, are stretched on a square that looks like a picture frame with spikes on the corners; caps are stretched over an upside-down U of bamboo. Amy Singer wrote an article in the Winter issue about how to attenuate and spin silk caps into yarn. Some companies also offer waste silk fiber called throwster's waste -- this is made of bits of thread that are waste from the throwing frames which twist the silk. Some throwster's waste is highly twisted, some is fairly soft -- it's basically a difference between whether it got snarled on the bobbin before the twisting part, or after. Occasionally throwster's waste is sold in the gum, but usually in the USA we get it degummed, and it looks kind of like washed cotton fiber. If you get waste that is gummy, it will make a smoother, less hairy yarn if you degum first and spin afterward. It's nicer on your fingers that way, too.

Species silks, or "wild" (actually semi-domesticated) silks, used to be very hard to find. Nowadays, hand knitters and spinners can get Tussah fibers and yarns in a wide range of colors and preparations, and some vendors even offer Eri and Muga yarns and fibers. Each of these is produced by a different species of moth. In India, which is where most of the wild silks are produced, they are called "vanya" silks; these silks each have a distinctive feel and color, and they are a treat for the hand spinner.

Tussah silkworms are much more hardy and wild than Bombyx. This is a Chinese Oak Tussah caterpillar in its fifth and final larval stage.

Tussah (also spelled Tasar, Tusseh, Tussore, Tussar) is the most popular and available type of wild silk here in the US. The designation actually covers a few different species of related moths, and biologists often use the term to refer to the whole genus. There are three main types of silk-producing tussah: the tropical tussah moth, Antheraea mylitta, lives in India and eats two trees called Asan and Arjun; the temperate or oak tussah moth, Antheraea pernyi, lives in China and eats oak, and the Himalayan silkmoth, Antheraea roylei, lives in the Himalayan forest region and eats oak.

Chinese Oak Tussah moths. Female above, male below. Tussah moths are strong fliers, and can have a wingspan of six inches.

A hybrid between roylei and pernyi has been created, called Antheraea proylei; it eats oak too, and makes a bigger cocoon with more silk. The hybrid moths are being used in Indian sericulture establishments, and they are being raised far outside of their natural range.

Tussah silks tend to be more textured than Bombyx, and they range in color from a pale rosy tan through a dark golden brown. Some varieties of tussah silk are bleached with peroxides to make them whiter so that they can be dyed to paler shades; I personally like the color of the natural silk. It takes dye beautifully -- just keep in mind that the original color affects the shades of whatever you dye over it!

Tussah caterpillars are raised outdoors on huge plantations of oak, Asan, and Arjun trees (according to their type and climate), and the cocoons can get nearly as large as a small hen's egg. The cocoons of the tropical tussah moth have a long peduncle, or stem, which the caterpillar makes by wrapping silk onto the stem of a leaf; the other types of tussah moth make a more compact cocoon with no stem. The tussah moths are large, with a wingspan usually of five or six inches, and are strong fliers. Although they are semi-domesticated, they have not been bred as much or as vigorously as the Bombyx, so they're much more hardy and need to live outside.

Muga silk comes from another moth in the tussah family. It is grown primarily in the Brahmaputra valley area of India, although efforts are being made to expand mugaculture into other parts of tropical India. The muga caterpillar spins a golden silk which is highly prized, and the reeled silks hardly ever leave India. But now, hand spinners in the West can get muga fiber to spin into yarn. It is darker and more yellow in color than most tussah silk, although personally it seems to me more brassy or bronze than gold. From the samples I've handled, muga also has a slightly more scroopy feel in the hand than tussah.

The Eri silkworm from India spins a fine, soft silk with a creamy white color.

Eri is the other well-known wild silk. It is not nearly as well represented in Western markets, but it is widely used in India. The moth, Samia ricini, which produces Eri silk is not closely related to the Tussah or Bombyx moths, and like Bombyx, it has been bred to the point that it is essentially a domesticated insect. Eri caterpillars eat a number of plants, including castor bean, manioc (tapioca) and kesseru. Because these are food crops, Eri silk raising is often used alongside of the food production, as a valuable side product.

Eri is rarely seen as a silk spinning fiber, although some specialty yarn shops (like Habu Textiles in New York) do carry Eri yarns. Eri silk is popular with many people who object to Bombyx silk because of the moths being killed; because of the way the Eri caterpillar spins its cocoon, the silk cannot be reeled, so the moths are often allowed to emerge instead of being stifled. The spun yarns are often more "cottony" than most Bombyx silks, although some roving-spun Eri yarns can be very soft and shiny. The Jain Buddhists refer to this as "ahimsa" silk, named after the principle of not harming any living thing. Many Westerners call this, and certain other types of silk raised without killing the moths, "peace silk."

There are wild silkmoths in America and Europe as well. It's a little extra work, but yarn can be made from the cocoons of several of the wild species. They take longer to degum than Bombyx silk, up to two hours for some types. I've raised half a dozen species of wild North American silkmoths. The best one for ease of rearing and quality of silk is Antheraea polyphemus, which is related to the tussah moths.

Silk offers the spinner a wide range of options, from the simple to the very challenging. It can be made into many different kinds of yarn, from lace weight to chunky, smooth to novelty. The history and mystique of silk, along with its beautiful look and touchable softness, make it a perfect fiber for many special projects.

Links:

aurorasilk.com - Master natural dyer Cheryl Kolander works with silk in a wide range of forms, from cocoons to fabric. Cheryl promotes "Peace Silk," where Bombyx mori are raised and bred without stifling.

habutextiles.com - Habu Textiles is an excellent source for hard-to-find specialty silk yarns, and specialty items such as Japanese silk reel bobbins.

littlebarninc.com - Little Barn is a good source for raw silk fiber. They're one of the few places that stocks Muga from time to time.

thesilkworker.com - Carol Weymar dyes and sells a range of silk specialty spinning fibers. Her silk hankies and caps are particularly renowned.

treenwaysilks.com - Karen Selk runs the largest distributor of silk specialty fibers and yarns in North America. This is the best place to get cocoons, and they have some great information as well.

wormspit.com - This is my own website on silk and silkworms.

Michael started raising Bombyx silk worms in 2001. Through extensive research, trial and error, and lots of perseverence, he learned to raise and care for these little caterpillars, and to turn their cocoons into glistening silken thread. Now he raises several types of wild silk worms in addition to the domesticated type, and enjoys the beautiful huge moths. He uses the silk to brocade his insanely tiny tablet-woven ribbons, and has been working on producing silk threads appropriate to other uses such as knitting.

Michael is thirty-six, and lives with his partner, Christopher, in the suburbs north of Dallas with two dogs, two cats, and a seasonal flock of tiny fiber livestock. He weaves, sews, knits, makes soap, spins,
draws, dances, and cooks, in the belief that specialization is for insects.