Silk | History, Production and consumption

Silk is one of the most precious textile fibres of animal origin, obtained from the flossy filament ejected by the silk worm of the butterfly Bombyx mori.

According to tradition, silk was discovered by a young Chinese empress, Hai Ling Shi, in 2640 BC. She noticed in her garden, on the branch of a mulberry tree, a small white cocoon, and brought it into the imperial palace to examine it more closely. Casually she dropped it into hot water and noted that a thin filament began to unwind. The court weaver was asked to do experiments with the new filmy fibre which kept unwinding as the empress pulled it; his trials resulted then in the weaving of the first silk dress.

 

Silk processing aims at obtaining from cocoons a yarn as uniform as possible. It should be pointed out that it is the only continuous filament existing in nature. Raw silk consists by 60-70% of fibroin ( a white coloured protein), by 20-22% of sericin and, for the rest, of gummy substances, minerals and dyestuffs.

Before the pupa changes into a butterfly, cocoons are submitted to a first selection to eliminate the faulty ones and remove their outer layer (floss silk); then they are kept 16- 18 hours in drying ovens to cause the pupa's death and to eliminate moisture which would jeopardize their preservation.

The next operation is the cocoon sieving aimed at removing the residual floss silk, which may however be used together with other types of waste: imperfect cocoons, flock silk, filoselle, broken silk in schappe spinning.

A second sorting is then carried out to divide the cocoons into three size categories, which will be reeled separately because the smaller the filament diameter, the smaller the corresponding cocoon. After softening by immersion in warm water to facilitate the filament extraction, the cocoons are brushed to find the tail end of the filament and to remove from them the top layer of hair (flock silk). Once the tail ends are found, the cocoons are unwound until reeling begins to take place without difficulty. Degumming is followed by filament reeling, which produces a yarn composed of several filaments depending on the required yarn diameter. Once the yarn is twisted, it is wound with helical angle on reels, which are generally contained in special boxes which are closed and heated to enable yarn drying. The dried yarn is packed into skeins and put on the market under the denomination of raw or ecru silk.

Production and consumption

During the past 30 years, the world production of raw silk has steadily grown; this was however associated with a deep change of the production structure in terms of producing countries. In fact in 1970, with a silk world production amounting to abt. 40.000 tons, Japan accounted for the highest share with more than 50% (20,500 tons), followed by China (10,200), Soviet Union (3,000), South Korea (2,850), India (2,250). At that time, Italy still ranked among the producing countries with 310 tons.

On the contrary, today, the estimates of the International Silk Association show a global production of abt. 100,000 tons, where China is the leading producer with 70,000 tons (70%), whereas in Japan the production declined sharply to abt. 4,000 tons (4%). India, with 13,000 t, has therefore overtaken Japan and is now in second position, followed by CIS, Brazil and North Korea.

Among the "other" countries, let us mention Thailand, Turkey, South Korea, Vietnam, Indonesia and Paraguay.

Italy continues to rank among the leading importing countries of raw silk, which is converted, thanks to the skill of its domestic silk industry and to the high-tech Italian machines, into ply and schappe yarns, also blended with other fibres, into silk and bourette fabrics, scarfs, foulards and ties, which have made the Italian design renowned all over the world.

The main silk producing countries (1996)