Nature of Silk Fiber

The perfect raw silk fiber is a very fine filament with two parts that can readily be seen under a microscope. This filament is composed of a substance called fibroin, and the outside is covered with a waxy substance called sericin. Silk fiber in its raw state is for its size the strongest textile fiber in existence.It is said that it is as strong as an iron wire of the same size would be. Notwithstanding that in the processes of manufacture much of this strength is lost, unless very badly treated, the fiber remains remarkably strong. It is also very elastic and durable. It has a high natural luster which is improved upon in some manufacturing processes. The fabrics into which it is made are beautiful even in the natural silk colors.Absorptive power of silk.-Silk fiber readily absorbs water; wherefore, in commerce, rules are necessary regarding the amount of water allowable in the fiber offered' for sale. The usual amount allowed by weight is about eleven per cent.It can easily be understood that when raw silk fiber sells for more than three dollars a pound, a large fraction of the total weight, such as one-third, one-fourth, one-fifth, or even one-tenth of water, would make a big difference in the price. Silk markets, therefore, are always equipped with the necessary apparatus for telling just what part of the weight of the silk is water. For example, the Silk Association of America has a large laboratory in New York in which the principal work is the determination of the proportion of moisture in raw silks brought from the market. The process of getting the silk into the proper standard condition as regards moisture is called "silk conditioning."