Cultivating, Curating, Producing and Harvesting Silk For Weaving Rugs
Most commercial silk is harvested from the Bombyx mori, which is also known as the mulberry silk moth, or more colloquially as the silkworm. The silk, an animal protein fiber, is produced by the moth when it is in its larval or caterpillar stage. It is not literally a worm, but bears some resemblance to a worm at this stage of its life cycle.
Silk has been produced by domesticated species for thousands of years. The Bombyx mori was domesticated from the wild Bombyx mandarina, and eventually came to differ substantially from it. The Bombyx mori has lost its pigmentation and its ability to fly, and is largely dependent on humans for its reproduction.
Life Cycle of the Silkworm
Cultivation of silk from domestic silkworms is called “sericulture.”
The first stage of the silkworm life cycle, and hence the first stage of the sericulture process, is the laying of eggs. This is typically done in an aluminum box or other container. Each egg is as tiny as a pinhead. An adult female silkworm (that is, one that is in the moth stage of its life cycle) typically lays 300-400 eggs at a time. It dies almost immediately upon laying its eggs, and the adult males die shortly thereafter. In fact, the adult stage of the life cycle is very brief; the adults possess only a rudimentary mouth and do not even eat.
The eggs are examined carefully for any sign of disease. If no such problems are detected, they are incubated for about ten days.
When the eggs hatch, this commences the larva stage. The caterpillars are only about a quarter inch long when they emerge from the egg, but they grow rapidly to a size of about three inches as they do little more than eat constantly during this stage. The caterpillar will ultimately eat about 50,000 times its initial weight.
A fine layer of gauze is placed over the caterpillars when the eggs hatch. They are fed primarily chopped white mulberry leaves, hence the alternate name of mulberry silk moth. Lettuce, Osage orange, and other plant material is also sometimes used as feed. The caterpillars eat and grow for about six weeks, shedding their skin four times along the way.
At this point, the caterpillars are ready to spin their cocoons, which takes three to eight days. This is when the silk is produced.
The silkworm climbs up onto some sort of frame that has been provided for that purpose in its container. A pair of salivary glands in the silkworm called “sericteries” produce a clear, viscous fluid called “fibroin,” while another pair of glands produce a gummy fluid called “sericin.” The silkworm forces these substances through openings—spinnerets—in its mouthpart. The fibroin secretions harden immediately when exposed to the air, forming twin filaments. These filaments are then immediately bonded together by the sericin.
This is the silk of the silkworm.
For the next several days, the silkworm meticulously builds its cocoon with this silk, following a figure-8 path hundreds of thousands of times. Over the course of this time it produces approximately one kilometer of silk.
Harvesting the Silk
At this point, the cocoon is carefully heated to loosen the silk. The silk is softened, and then gradually unwound. Generally the silk of four to eight cocoons is unwound together, forming one thicker strand.
Through a process called “throwing,” the raw silk is then twisted into a strand strong enough not to split into its constituent fibers. This renders it suitable for knitting or weaving.
There are four different common types of silk thread produced this way, each by a slightly different method of throwing. Crepe is produced by twisting multiple threads together, and then twisting them a second time. Tram is produced similarly, but the silk threads are only twisted in one direction instead of two. Thrown singles are produced with just one thread rather than multiple. Like tram they are only twisted in one direction. Finally, organzine is produced by giving individual silk threads a twist before combining two of them and twisting them in the opposite direction.
Crepe thread is used for weaving wrinkly fabrics, tram thread is used for the weft part of the weaving process, thrown singles thread is used for sheer fabrics, and organzine thread is used for the warp part of the weaving process.
Raw silk still contains the binding agent sericin. Soap and boiling water are then used to remove this sericin. This leaves the silk as much as 30% lighter than the raw silk, as well as softer and more lustrous.
Though a kilometer of silk from each cocoon sounds like a great deal, in fact very little survives this process as usable silk. It typically takes about 2,500 silkworms to produce one pound of raw silk.
Filaments that cannot be used as silk can be salvaged and processed into a cheaper type of yarn called “spun silk.”
Alternatives to Silkworms For Cultivating Silk
Many other animal species produce silk. Silk is produced by many species of bees, wasps and ants, often for nest construction. Most famously, spiders and other arachnids use silk to spin their webs.
None of these other species have been used for commercial textile production, though research continues into whether any such alternative to the silkworm might be viable. Already the silk from some of these other animals has been used in weapons and optical instruments such as telescopes.
Weaving Rugs Using Silk
As noted above, silk is an animal fiber that is derived from the cocoons of silkworms. It is an extremely costly and luxurious material for textile and rug production. Cultivation of these fibers began in ancient China where it was a jealously guarded secret. Eventually its use spread to Persia and then to Byzantium and Europe.
The expense notwithstanding, rugs with silk pile and or foundations, are not uncommon, although they tend to be high quality pieces in the tradition of court art.
Extremely luxurious nomadic carpet weaving have been known to use the fibers as a sign of class and significance. The attraction to these rugs resides in the fineness of its fibers which are remarkably soft, as well as in it’s luminous, reflective quality.
Because of this the effect of color on silk is far more intense and brilliant than the effect of the same dye on even the finest wool. These fibers when treated (see below) are much more delicate and less durable than wool.
Consequently, many less silk rugs are well preserved. This rarity, as well as the basic cost, places antique silk pieces among the most expensive rugs.
These fibers were bought and sold by their weight. As such, some traders would treat the fibers with metal. This metal treatment, increased the overall weight which resulted in more money for the dealer.
Unfortunately, the metal corrodes with time. This is what causes some antique carpets to “break”. So when buying these types of antique rugs, it is important that the piece be in excellent starting off condition – that is a great sign that the fibers have not been treated and should last for many generations to come.