Silk is the fibrous material in which the silkworm, or larva of the moth, envelops itself before passing into the chrysalis state. Silk is closely allied to cellulose and resembles wool in structure, but unlike wool it contains no sulfur. The natural silk is covered with a wax or silk glue, which is removed by scouring in manufacture, leaving the glossy fibroin, or raw-silk fiber. The fibroin consists largely of the amino acid alanine, CH3CH(NH2)CO2H, which can be synthesized from pyruvic acid. Silk fabrics are used mostly for fine garments, but are also valued for military powder bags because they burn without a sooty residue.
The fiber is unwound from the cocoon and spun into threads. Each cocoon has from 1829 to 2743 m of thread. The chief silk-producing countries are China, Japan, India, Italy, and France. Floss silk is a soft silk yarn practically without twist, or is the loose waste silk produced by the worm when beginning to spin its cocoon.
Satin is a heavy silk fabric with a close twill weave in which the fine warp threads appear on the surface and the weft threads are covered by the peculiar twill. Common satin is of eight-leaf twill, the weft intersecting and binding down the warp at every eighth pick, but 16 to 20 twills are also made. In the best satins a fine quality of silk is used.
