F r o m   y a r n   t o . . .

Silk reeling.

After the chrysalis has been stifled and dried, three more operations are required before reeling : the cocoons are cooked in water at nearboiling temperature so as to soften the gum (sericin) on the outer layers, mechanical brushes then beat the cocoons to loosen the floss, a mass of short fibres on the outside of the cocoon, purging : removing the floss and picking up the end of the continuous filament forming the cocoon, which can reach 1,600 metres in length. Once the cocoons have been thoroughly prepared in this way, they are placed in a reeling-basin in which the water is kept at a temperature of 50°C (122° F). The silk reeler assembles the baves of 4 - 12 cocoons, according to the thickness of yarn required. The thread thus assembled is fed over a series of pulleys and at the same time is very lightly twisted (‘croisure’) to ensure good cohesion between the baves. It is then taken up on a reel or swift, a sort of very large bobbin. The reeler has a very important job namely keeping a close watch on the formation of the silk thread, because as soon as one cocoon is ‘empty’ a new one must be added so as to maintain a constant diameter, one of the chief quality characteristics of raw silk. Nowadays the silk reeler is often replaced by an automatic reeling-machine which is equipped with sensors allowing for the immediate replacement of empty cocoons or broken filaments. The yarn obtained after the reeling stage is known as raw silk. It is packaged on skeins.
Spun silk, silk noil. Silk is too precious to be wasted and every attempt is made to recover cocoons unusable for reeling, as well as broken filaments and floss. These elements of silk waste are gathered together and partially degummed before being carded and combed in the same way as wool and other natural fibres. The resulting bands of fibre, slivers, are then spun into yarn : the longer filaments become spun silk (or schappe) the shorter filaments become noil. (N.B. The English language uses ‘reeling’ for continuous filaments and ‘spinning’ for short fibres).

Douppion (dupion). It sometimes occurs that two silkworms which are too close to each other spin a double cocoon instead of two single ones. The thread from these double cocoons is so entangled it cannot be reeled in the normal way. A special reeling technique has to be used, which gives a coarse, uneven yarn. When woven, this makes for an irregular effect which is highlyprized in applications such as bridal wear.

Wild silks.

Bombyx mori is not the only silk-producing insect. There are numerous varieties of caterpillars living in a wild or semi-domesticated status and producing silk. In Manchuria and India for example wild silk known as tussor or tussah is produced from the caterpillars of a moth which lives on oakleaves. India also produces two native varieties of wild silk called muga and eri.

 Raw-silk classification. Raw silk is classified according to international standards. This classification determines the price and the applications of the yarn. The yarn is classified according to its titre (size), measured in deniers. (1 denier = the weight in grammes of 9,000 metres of yarn). Within each size category, the quality of the yarn is estimated on the basis of a large number of criteria such as evennness, neatness, cleanness, cohesion etc. These qualities are translated into grades whch are expressed in letters, e.g. China 3A, 20/22. this means raw silk from China, of grade 3A, 20 - 22 deniers in size.

 Thrown silks. Raw silk yarns, single-ply, are used as such for certain types of fabric, but generally single-ply yarns are assembled and twisted to form the warp . This operation is called throwing (or twisting) and is designed to give yarns more bulk, or more strength or a certain feel or appearance after weaving. Some examples of thrown yarn are : Poil (or single) : a single-ply yarn twisted up to 3,000turns per metre (tpm). Tram : an assembly of several single yarns, twisted up to 100 - 300 tpm. Organzine : two or more yarns, twisted right-to-left, are assembled and twisted leftto- right.