Silk and Silk Rugs

By Aaron Groseclose

Silk is synonymous with luxury and splendor. Over the centuries it has reigned as the undisputed queen of luxury textiles. It has been woven into tapestries, rugs, fine fabrics, and accessories for over 4,000 years. Sericulture (the cultivation of silkworms for silk) has remained virtually unchanged over the centuries. 

Silk was discovered around 2,600 BC in China. According to legend, an empress accidentally dropped a cocoon into a cup of hot tea. The heat melted the gum holding the cocoon together, and she discovered the cocoon unraveled into one continuous fiber. Chinese silks found their way to Rome and Greece, traveling over the 6,000 mile "Silk Road." Despite China's attempts to keep the secret of silk production to itself, it spread to Japan in the 3rd century AD and India in the 4th century AD. Marco Polo is credited with introducing silk production to Venice. To this day, Italian silks are renowned for their impeccable quality and workmanship.

What makes silk fabric look so spectacular is the structure of the fiber. It is produced by the silkworms, which actually are caterpillars and belong to two families: Bombycidae (the commercial silkworm) and Saturniidae (the wild silkworm). The most common source of silk, Bombyx mori, is raised domestically, but only where there are mulberry leaves to satisfy its finicky appetite. 

More than 500 species of wild silkworms fend for themselves, eating oak and other leaves. When they become moths, they are bigger than commercial Bombyx. More robust than their domesticated cousins, wild silkworms produce a tougher, rougher silk, not as easily bleached and dyed as the mulberry silk. The leaves they eat are full of tannin that colors the silk, giving it a beige look. Wild silk is usually called Tussah silk, however, there are many kinds of wild silks, each with its own characteristics. Wild silk is usually less expensive than cultivated white silk.

Two glands in the silkworm produce a liquid silk that is made up of giant protein molecules called fibroin. The fiber is coated with a sticky substance called sericin that holds the cocoon together. The strand can be up to a mile in length and is extruded through a narrow aperture on the worm called the spinneret. The biers have a slight prismatic, rainbow effect. 

Silk has three properties that make it unique. Hygroscopicity - it has the ability to absorb moisture without feeling wet, holding up to 30% of its dry weight in water. Low specific gravity - it has a low density. The molecular structure resembles a long string of ladders. Between the "steps" is air space. These act as insulation and allows the fiber to breathe. Strength-in-fineness - silk's extraordinary fineness can be used to weave fine fabrics and rugs with up to 3,000 knots per square inch. Its strength, given equal diameters, is stronger than any other natural fiber, including nylon or steel wire. Also, silk will not weaken when wet like rayon and other synthetics. 

As strong as it is, silk is subject to wear through abrasion. It is stronger than cotton or fine wool like cashmere, but it is not as durable to abrasive wear as the bast fibers or coarse wool. As a result, silk carpets are for reclining, touching, but not for walking - except maybe barefoot. 

Silk is resistant to various molds, mildew, and dry rot that attack other fibers. It is damaged by long periods in direct sunlight, as are all fibers. The wool moth does not attack silk. Silverfish and some carpet beetles will eat silk. 

Silk, as it comes from the cocoon, is coated with a protective layer of sericin or silk gum. This coating may be any color: white, yellow, brown, beige; its color is not related to the color of the silk beneath it. The ilk gum is dull and stiff, so it is usual to remove it to reveal the pure fiber luster. Silk with all its gum is called raw silk. This should not be confused with the fashionable "raw silk" fabric actually woven from noil silk, which is made from very short fibers and little tangle-balls of fiber. Generally noil is a weak yarn with little elasticity and is only used for fabric. We have two basic types of silk yarns, the thrown and the spun. They correspond to the two basic forms of the fiber, reeled (continuous) and cut (staple). 

How to reel silk was one of the great Chinese discoveries. The cocoons float in a basin of hot water to soften the gum, allowing the thread ends to come loose. They are often plied together - five to eight filaments at a time - then fed into the reeling machine and put onto a spool. "Throwing" is the process of twisting the unspun filaments of reeled silk. It is almost always made from cultivated silk.

Spun silk is made from wild cocoons. The silkworm exudes a brown liquid enzyme that softens the cocoon, enabling it to push outside. This ruins the cocoon for reeling, now becoming a staple fiber. Cultivated silk cocoons are exposed to steam to kill the living pupae. After degumming of the cocoon, it is carded and combed. Then it is twisted into singles, then plied to make the yarns. The process is similar to making cotton or wool yarns. 

Wild silk traditionally has been used for pile fabrics and rugs.Most Chinese rugs seem to be made from spun wild silk. The finest silk rugs, such as the ones from Hereke, Turkey, are made from reeled silk. The fine threads made from the continuous fibers are used for the foundation and the rug face, allowing the knot count to exceed 3,000 per square inch. 

Wet cleaning of moderate to lower priced silks is generally plagues by pile distortion and fugitive dyes. A possible explanation is the silk used for these problem rugs may be noil silk. Noil is the very short fiber left after the longer staple silk has been combed out. It consists of smooth fibers 1" long and shorter, sometimes mixed with tangled balls of fiber. Because of the very short fibers, noil yarns are weak and inelastic. Noil has a reputation of wearing out quickly as the very short fibers disintegrate more rapidly than do intact long fibers. 

Another factor in pile distortion on silk rugs can be heat. Silk fibers can withstand high temperatures (330° F or 166° C), but due to the minimal twist found in plush staple silk yarns, temperatures should be limited. 

Unbleached, cultivated silk noil usually has small black flecks appearing throughout. These flecks are the crumbled remains of the chrysalis, that horn-like envelope that encloses the transforming silkworm inside the cocoon. Noil often is bleached and then dyes well. Again this yarn should be used for garments or fabrics, not rugs. In the past China has been known to use garment wool for rugs, resulting in poor resiliency and wear. Due to this past practice, certain Chinese rug producers may be using noil for rugs. This would account for the severe pile distortion which occurs on certain cheaper rugs after cleaning. 

Reprocessed silk is made from silk waste from any source including mill floor sweepings. The yarn is pulled apart, carded, and spun like noil. The fibers appear very non-uniform and may have bits of fine yarn mixed with it. The final yarn may be over-dyed by the spinner. 

Finishes are sometimes applied to silk fabrics. Sizing is an accessory to finishing and weaving. Some fabrics need its strengthening effect or they will fray or fall apart. Sometimes the crispness it gives is wanted. Sometimes sizing has been used on cheap manufactured silk fabrics to give them more body. This is put on rather heavily, dried, then "broken in," which breaks the glue between the yarns and softens the fabric so that it passes for a soft silk that feels more substantial than it really is. Sizing is not commonly applied to the face yarns of rugs. 

The weighting of silk is an old practice that is wholly objectionable. Fortunately, it is hardly done anymore. Weighting means the addition of metal salts (like iron, tin, or lead) to the dye process to increase the finished weight of the fabric. This was done as silk was sold by the pound, and in fact defrauded the buyer. The excess metal salts would cause the fabric to disintegrate after a short time.

Unfortunately, rayon and mercerized cotton are sold to the consumers as silk. Even to the professional cleaner, rayon can have a sheen that appears, at first, to be silk. Reading a label on a rug can also be misleading as the term "Art Silk" is used for artificial silk and "Faux Soie" is French for fake silk, both are rayon. The only way to be certain is perform a chemical or burn test. The burn test is quick and very accurate (The chemical test is to put some of the fibers in chlorine bleach - it will dissolve completely). Silk has a slight burning hair smell and a distinct ash - it generally forms a hard bead. Rayon and cotton, both cellulose fibers, have a very fine ash and smell like burning paper. 

 

Chinese Silks

China has always produced silk rugs in the past, and there are still examples of older good quality rugs the cleaner will encounter. The bulk of today's production is a 90 line quality, which means that there are 90 yarns of warp to one foot (31 cm) of width. There are also quite a good number produced in a 130 line quality and even finer. The finer quality pieces being made in silk are in Persian styling and can be difficult to differentiate from silk rugs from Iran. 

Kashmiri Silks

Kashmir is a province of India and has a long history of fine weaving. Today, Kashmir is turning out a considerable number of finely knotted silk rugs that are of top quality. The knotting is extremely fine and densely packed, with the pile left long, averaging about 1cm (about ½") in length. This gives a rug good bulk but the pile is not so long as to blur the design. Designs are all modeled on intricate Persian, Turkish, and old Indian carpets. Most sizes are 5'6" x 3'6" and some 6'6" x 4'6". 

Egyptian Silks 

Egypt has become an important rug weaving country, but its silk rugs do not have an international reputation. Many of the weavers are commissioned by Turks, and the rugs are exported exclusively to companies based in Hereke. Good quality silk is imported from China or Turkey and finely woven. The quality is good enough to be passed off as original Hereke work to the unsuspecting importer (read customer). 

Turkish Silks

The most expensive and well regarded new silk rugs on the market today are undoubtedly from Hereke. For more than a hundred years, Hereke has been known for its superb artistry in very fine knotted rugs. Most of the silk products coming from the looms of Herek today rank with their predecessors in the times when the Sultans of Turkey employed the finest weavers to make rugs for their palaces or gifts for dignitaries. 

Colorings are usually very delicate, often entirely in pastel shades. Occasionally, a rich ruby red, indigo blue, or deep bottle green color may be used along with metallic threads. These rugs are made in various workshops around the town of Hereke. Very fine, continuous filament thread from Bursa silk is used for both the pile and the foundation. Knot counts can reach 1,000,000 per square meter, or 3,000 knots per square inch. 

Kayseri is also a town in Turkey where rugs are made which uses identical designs and colors of Hereke silk rugs. Kayseri rugs can be distinguished by their coarser work and lower knot count. Good Kayseris can best be distinguished from Herekes by their knot count, which is always lower. Some Kayseris are produced with pile yarns of mercerized cotton. 

Persian Silks 

Persia has always produced silk rugs of many categories. Some of the best known are from the looms of Tabriz, Heriz, Kashan, Kirman, and Fereghan. Today the main producing area for silk rugs is the city of Qum. Production in Qum was on a large scale which is impacted by the US embargo against rugs from this country. Quality varies to a surprising degree, and each rug should be examined for quality of workmanship, fineness of knotting and design. 

The colors of Qum rugs is rather limited, with dark blue, pale gold, salmon pink, ivory, green, and brown being the main colors. Patterns vary from prayer rugs and hunting carpets to medallion designs. Sizes vary from 30" x 20" to 12' x 9'. 

In the past, Qum was known to import a lot of silk rugs from China, like the Egypt-HEreke trade route discussed above. This type of situation becomes obvious when a regions' rug production out-strips the number of looms. 

The cleaner will also see rugs from Nain, Isfahan, Sarouk, and Qum which have a wool pile with highlighting in silk. Although these rugs have relatively low silk pile weight, they command somewhat high prices. 

 

Guidelines for Cleaning Silk 

Silk fibers by themselves can be successfully wet cleaned. Problems arise with unstable dyes, damage from sunlight, special finishes such as sizing, and pile distortion. All of the cleaning methods can be used on silk, but the cleaner should carefully inspect the rugs and determine which method best fits the condition of the textile. 

The care of silk is similar to care of wool. Silk's luster is the quality most sensitive to damage. Careless handling may destroy the luster and eventually damage the durability of the fiber. 

All natural silk can be wet cleaned, except for some fabric with embossed or moiré designs. However, prior to cleaning, testing of the solution in an inconspicuous area is mandatory. The dyes used may not always be colorfast. If the dyes are not fast to wet cleaning test a dry cleaning solvent. However, be careful with hand painted silk fabric, as dry cleaning solvents will often remove these. 

When wet cleaning silks, use a detergent in the neutral pH range. Never use chlorine bleach on silk. It is very alkaline and will dissolve the fiber. If bleaching is ever required, use 3% hydrogen peroxide. 

If pile distortion has occurred in an oriental rug from wet cleaning, use live steam and a grooming tool to correct this problem. Be patient, because it will take time to correct the problem. Hand held steamers do work well.


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