COUNTRIES WHERE SILK IS PRODUCED

Production of silk involves (1) the care of the domesticated silkworm (Bombyx mori) from the egg stage through completion of the cocoon and (2) the production of mulberry trees that provide leaves upon which the worms feed. The silkworm caterpillar builds its cocoon by producing and surrounding itself with a long, continuous fiber, or filament. Liquid secretions from two large glands within the insect emerge from the spinneret, a single exit tube in the head, hardening upon exposure to air and forming twin filaments composed of fibroin, a protein material. A second pair of glands secretes sericin, a gummy substance cementing the two filaments together.

Silk is a continuous filament within each cocoon, having a usable length of about 600 to 900 m (2,000 to 3,000 feet). It is freed by softening the binding sericin and then locating the filament end and unwinding, or reeling, the filaments from several cocoons at the same time, sometimes with a slight twist, forming a single strand. Several silk strands, each too thin for most uses, are twisted together to make thicker, stronger yarn in the process called throwing, producing various yarns differing according to the amount and direction of the twist imparted.

Silk containing sericin is called raw silk. The gummy substance, affording protection during processing, is usually retained until the yarn or fabric stage and is removed by boiling the silk in soap and water, leaving it soft and lustrous, with weight reduced by as much as 30 percent. Spun silk is made from short lengths obtained from damaged cocoons or broken off during processing, twisted together to make yarn. The thickness of silk filament yarn is expressed in terms of denier, the number of grams of weight per 9,000 m (9,846 yards) of length.

Silk has good strength, resisting breakage when subjected to weights of about 4 g (0.5 ounce) per denier. Wetting reduces strength by about 15–25 percent. A silk filament can be stretched about 20 percent beyond its original length before breaking but does not immediately resume its original length when stretched more than about 2 percent. Silk, lower in density than such fibers as cotton, wool, and rayon, is moisture-absorbent, retaining as much as a third of its weight in moisture without feeling damp, and has excellent dyeing properties. It is more heat-resistant than wool, decomposing at about 170° C (340° F). Silk loses strength over a long period of time without appropriate storage conditions and tends to decompose with extensive exposure to sunlight but is rarely attacked by mildew. It is not harmed by mild alkaline solutions and common dry-cleaning solvents. Friction imparts a static charge, especially in low humidity. The rustling sound associated with crisp silk fabrics is not a natural property of the fiber but is developed by processing treatments, and it does not indicate quality, as is sometimes believed.

There are 58 countries where more or less silk is produced (total silk producing countries are more than 200). The following are the countries silk is produced:

Afghanistan, Algeria, Argentina, Bangladesh, Bhutan, Brazil, Bulgaria, Burma (Myanmar), Chile, China, Colombia, Conga, Egypt, Ethiopia, France, Ghana, Greece, Hungary, India, Indonesia, Iran. Italy, Ivory Coast, Japan, Kenya, North Korea, South Korea, Laos, Lebanon, Madagascar, Malaysia, Mauritius, Mexico, Morocco, Nepal, Nigeria, Pakistan, Papua New Guinea, Paraguay, Kampuchea, Peru, Philippines, Poland, Romania, Spain, Sri Lanka, Syria, Tanzania, Thailand, Tunisia, Turkey, Uganda, Russia, Venezuela, Vietnam, Yugoslavia, Zambia, Zimbabwe.