In silk manufacture, the first operation is reeling. The cocoons, having been sorted for color and texture, are steamed or placed in warm water to soften the natural gum. They are then unwound; each cocoon may give from 2,000 to 3,000 ft (610–915 m) of filament, from 4 to 18 strands of which are reeled or twisted together to make an even thread strong enough to handle. This is called raw silk. Formerly a hand process, this work is now done in Europe and in some parts of the Orient in factories on simple machines called filatures.
The next step, called throwing, is preparing the raw silk for the loom by twisting and doubling it to the required strength and thickness. This process also is now mostly done in large mills with specialized machinery. Silk, after throwing, has three forms—singles, which are untwisted, used for the warp of very delicate fabrics; tram, two or more singles, twisted and doubled, used for the weft of various fabrics; and organzine, made of singles twisted one way, then doubled and twisted in the opposite direction, used for the warp of heavy fabrics. For sewing and embroidery thread, more doubles and smoother twists are made. In modern factories spinning frames complete the preparation for the loom.
The silk is boiled off in soapsuds to remove gum and prepare it for dyeing. For white and pale tints it must be bleached. Scouring or boiling causes loss of weight, sometimes made up by loading with metallic salts, as tin, which has an affinity for silk and can be absorbed to excess, causing weakening of the fiber. Dyeing may be done in the yarn or in the piece. Finishing processes are varying and important, as in making moires. Weaving is done as with other textiles, but on more delicate and specialized looms.
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