2. Spun Silk
Spinning Waste Silk
The above processes refer only to throwing of raw silk. In the case of waste, schappe, frisons, etc., an entirely different method must be used, comprising a series of operations very similar to the carding, combing and spinning of wool.[8] The gum, of which silk waste contains a very large proportion, must first be boiled off in a hot soapy bath or allowed to ferment in vats, the latter method being used more generally in Europe. After degumming, the waste silk is next washed and dried and allowed to absorb the 11 per cent moisture content, as in the case of the thrown silk. This is followed by picking, combing, and dressing to remove any dirt or other foreign matter and to separate the fibres and arrange them in parallel order.
The silk is next separated into short laps, then drawn out into thin slivers by means of drawing frames, and thoroughly combed to make the fibres smooth and uniform. These slivers are finally made suitable for winding on bobbins by being passed through roving frames. Then follows the actual spinning process, which twists the roving into yarn. Different types of yarn are produced by varying the amount of twist and the number of strands used. Single yarn is made by twisting a single strand on itself, while for 2-ply, two yarns are twisted together, and so forth, as in the case of cotton or wool.
After being cleaned and examined, the yarn is wound into skeins of about 5 ounces.
Uses of Spun Silk
The principal use of spun silk is in mixed fabrics, in conjunction with wool, cotton, or raw silk, the spun silk thread generally being used as filling rather than warp. The better grades are made into velvet and plush and various types of knit goods. Although high quality spun silk often has the strength and wearing quality of thrown silk, it never can compete with the latter in regard to lustre.
Sizing
Spun silk is described as to size in one of two general ways. In the English system the number of the yarn is the number of hanks of 840 yards weighing a pound, with a second number indicating the ply. Thus, size “20-2” would designate a 2-ply yarn, a pound of which contained 16,800 yards. The French system is more or less on the same principle, the main difference being that the number of the yarn indicates the thousands of metres weighing a kilogram.