Silk, a thin natural protein fiber produced by the caterpillars of some butterflies (silkworms) during the construction of the cocoon at the transition from the developmental stage of the larva to the pupal stage, and before the transformation into a butterfly. It is obtained by unrolling the thread of the cocoon and a natural filamentous fiber is formed, ie a fiber of great length (several hundred meters). The most important and highest quality silk is silk mulberry, which is the only silk grown in order to obtain silk.
Silk production
The millennia-old art of growing silk mulberries and separating threads from cocoons has been preserved to this day, and silk is still acquired in an almost unchanged way. Fertilized silkworm eggs are placed in incubators, after 2 to 3 days small caterpillars (about 2 mm long) hatch from them and feed immediately on fresh mulberry leaves. They are very voracious, eat huge amounts of leaves and grow to a length of 80 to 90 mm in 30 to 35 days. When the caterpillar reaches full growth, it begins to secrete a double thread (fibroin thread) wrapped in protein (sericin) from the two openings in the head. With proper movements of the head in the shape of an octagon, the caterpillar wraps itself around this thread, creating a cocoon. Sericin, which makes up about 25% of the silk mass, acts as an adhesive and binds two fibroin threads into one solid thread that hardens in air. This creates a compact cocoon, within which the caterpillar transforms into a butterfly within 14 days. In the natural life cycle, the developed butterfly emerges from the cocoon and the reproductive cycle begins anew, while in breeding the butterflies are killed so that they do not destroy the silk thread when they emerge. At the beginning of processing, the cocoons are softened in warm water, and the outer, lower quality layer in which the silk thread is tangled is first separated. From this part, as well as from the part closest to the interior, short hairy silk fibers paw, floret and barrel are obtained. These fibers are used in textile processing to produce yarns of the same name and fabrics for summer suits and costumes, which are characteristic of their natural appearance. After removing the outer layer of the coil, tapping with a stick or a rotating brush finds the beginning of the thread and starts unwinding, combining the threads with five to ten coils, depending on the desired fineness of silk yarn and further processing for which it is intended. With such unwinding, it is possible to obtain a continuous silk thread 900 to 1000 m long. Due to the sericin it also contains, such a silk thread has an inconspicuous appearance, greenish-yellow color and relatively rough to the touch, and is called raw silk or grez. More threads of such silk can be finished in subsequent processes with a different number of turns, resulting in finished silk yarns tramin, organcin and grenadine, from which, as a rule, quality silk fabrics are made, and less often knitwear. In order to finally achieve the highly valued aesthetic features of silk fiber and clothing, ie smoothness, fineness, noble shine and above all a pleasant touch and touch, it is necessary to remove sericin from silk threads, which is achieved by degumming. This is the treatment of raw silk (usually in the form of fabrics) in a soap solution of slightly elevated temperature in which sericin is soluble and is removed partially or completely, depending on the need and purpose of silk. Depending on the degree of degumming, there are several types of silk: kvite is the name for silk whose degressing removes all sericin (loss of weight during processing 25 to 30%), suple is silk whose degumming removes about 12% of the mass (close to half the total amount of sericin) , and in the case of silk called ekri, only a small part of the sericin was removed. Very light fabrics made of degummed silk sometimes need to be made heavier (matlase, brocade) in order to achieve the best possible fall, which is done, for example, with phosphate-based products or tannins, sometimes up to the weight it was before degumming.
In addition to silk mulberries, which produce the highest quality silk, there are about eighty species of butterflies whose caterpillars create cocoons of silk thread, and which live freely in nature (forest areas of China, India, Japan and parts of Africa). The cocoons of these caterpillars are usually much larger and the separation is not even easier, but the silk obtained is not as high quality as the silk of silk mulberries, so products made of such fibers are cheaper. For this group of silk fibers, which are obtained from cocoons collected from silks that live freely in nature, the general name of wild silk is used, and the most famous of them are: tusah, erija, anafe, kurivata, fagara and others.
History of silk
The homeland of silk is China, where mulberry silk has been cultivated for a full five millennia, and the art of obtaining silk was developed and nurtured at imperial courts and kept in strict secrecy; therefore, China has had a monopoly on silk production for more than two millennia. From there it was traded all over the world (the Silk Road is known, the land traffic route by which it arrived in Europe), and silk became a term of exclusive and expensive material in which emperors, kings and nobility dressed. However, around 300 BC. Kr. mulberry silkworm arrived in Japan, around 200 BC. Kr. to Korea, and thence to India and Persia. According to historical sources, silkworm eggs and mulberry seeds were smuggled into Europe (Byzantium) in 552, and Byzantium soon became the European center of silk production and held this monopoly from VII. to XI. However, after the conquest of Persia in the VII. century, the art of silk farming was transferred to Sicily and Spain, and from there silk production gradually spread to the interior of Europe. In some parts of Croatia, such as the hinterland of Dubrovnik, on the islands of Krk, Cres, Pag and Rab, silk was produced in the Middle Ages, and in the 19th century. century, after the encouragement of Empress Maria Theresa, especially spread to northwestern Croatia and Slavonia, but due to the plague that affected the mulberry silk, silk production in these areas ceased after some time.
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