Sewing silk is made by winding and doubling the raw product, then twisting into tram, giving it a slack twist, doubling and twisting in the reverse direction under tension. Machine twist is similar, but three ply.
The principal fabrics made of silk are: silk, satin, plush, chenille, crêpe, crepon, gauze, damask, brocade, pongee, and ribbons. Silk thread and cord are also extensively used. The United States is among the leaders in the manufacture of silk fabrics.
=Silk Waste.= When the cocoons are softened for reeling a certain portion of the silk is found to consist of waste and broken threads. The tangled silk on the outside of the cocoon is called floss. The residue after reeling, and other wastes in reeling, are known as frisonnets. Floss silk is not used for weaving. It is a slack twisted tram, generally composed of a large number of threads of singles.
=Spun Silk.= There is another class of threads made from waste silk by spinning and known as spun silk. Waste silks include the pierced cocoons, that is, those from which the moth has come out by making the hole and breaking the fibers in one end of the cocoon; the waste made in the filatures in producing raw or reeled silk, chiefly the outside fiber of the cocoon and the inside next the chrysalis; and also the waste made in manufacture. The waste silk is ungummed; that is, the gum is removed from the fibers by boiling with soap, by macerating or retting, or by chemical reagents.
After the gum is removed from the cocoons, they are opened and combed, most of the chrysalis shell being removed. The remainder, with other foreign matter, is picked out by hand from the combed silk. The silk is put through a number of drawing frames to get the fibers even on the roving frames, where it first takes the form of thread, then on the spinning frames, where it is twisted. If it is to be used as singles, the manufacture ends here. In two- or three-ply yarns, the singles are doubled, twisted again, singed by running through a gas flame, cleaned by friction, controlled, that is, the knots and lumps taken out, and then reeled into skeins for dyeing or put on spools.
=Spun Numbers.= There are two methods in general use for numbering spun silk. In the French system, the number is based on the singles, by the meters per kilogram; two and three cord yarns have one-half, one-third, etc., the length the numbers indicate. Thus--