A wide variety of natural fiber are used in oriental rugs. By far the most common are wool, cotton, and silk. Goat hair, camel hair, horsehair, yak hair, and jute are also used.
Some of these fibers can only be distinguished microscopically. With experience, wool, cotton, and silk can be identifies by their appearance and texture. In comparison to cotton, wool is less soft, more coarsely textured, and has more “spring” to it.
Undyed cotton has a hard white appearance compared to white wool. Silk is more flexible and glossier than either wool or cotton, although it is possible to mistake very glossy wool or mercerized cotton for silk.
As a group, vegetable fiber is much resistant to alkalis the animal fibers. Animal fibers will disintegrate in a string lye solution, while vegetable fibers will remain intact. This is one of distinguishing silk and cotton.
The most important qualities in wool are fiber fineness, fiber length, and natural color. These qualities are primarily determined by the breed of sheep, but they are also influenced by climate and pasturage.
The fineness of wool fiber ranges from a thickness of I/3,000 inch (I/7,620 centimeter) to I/275 inch (I/1698 centimeter). The merino and its crossbreeds regularly produce the finest wool, but fine wool is also taken in the first shearing of lambs from many breeds. Breeds producing coarse wools are generally found in the Middle East. Fairly coarse wools have better wear resistance than fine wools. When in doubt yarns or fibers, a small quantity can be burned. This test is reliable.
The use of cotton in the foundation of pile rugs is incredibly old practice. There are 17th-century Persian carpets with wraps and wefts of cotton. Indeed, most town or factory rugs have cotton warps. Undyed cotton is occasionally used for pile in small areas, where its hard white appearance provides contrast. Cotton is not generally used as an all-over pile fiber because of its tendency to mat.
Cotton is grown throughout the Middle East and Asia. Egyptian cotton is well known for its long staple, only exceeded in length by Georgia Sea Island cotton. Staple length varies from 3/8 inch (0.952 centimeter) to 2 ½ inches (6.35 centimeters), the longer being more prized.
Fiber of the cotton plant has the cross-section of a flattened tube. The fiber is naturally twisted, and this characteristic makes it easier to spin.
Mercerized cotton is cotton yarn treated with caustic alkali while the yarn is under tension. This process increases the luster off the yarn to such a degree that it may be mistaken for silk.
Silk is used in the pile and foundation of some of the costliest Middle Eastern and Chinese rugs. Silk is sometimes used for the pile in a rug with a cotton or wool foundation. In some Turkmen and Caucasian rugs, small colored areas of silk pile are found with an otherwise wool pile.
The principal source of cultivate silk is the cocoon of the moth, Bombyx mori. Filament from the cocoon is about I/I,200 inch (I/3,048 centimeter) thick, and from 800 to I,200 yards (730-I, I00 meters) long. Commercial silk from cultivated moths is initially classified as reeled or unreeled silk. Reeled silk is unwound directly from undamaged cocoons floating in a hot water bath and is made up of along parallel filaments before it is spun. This pearly soft-white silk is the finest and most highly valued. Unreeled or spun silk comes from damaged or stained cocoons The cocoon filament is loosened by fermentation or washing. After cleaning, the tangled filament is combed and then spun.
Wild or tussur silk, from a variety of moth species, is collected and processed in remote areas of the Orient and the Middle East. Tussur silk is usually gray, but it can be brown or orange depending on the moth species. This type of silk dyes and only takes darker colors successfully.