Silk is commonly known as the fiber of luxury. It is the most expensive to cultivate, the most beautiful, and the strongest fiber. Since it is the most expensive to buy, and the demand for it is so large, the temptations to adulterate are also naturally very great. The long, strong, lustrous silk fiber which bleaches and dyes beautifully, and is fine as a spider's web is not to be duplicated (Fig. 60). The best grade, or "reeled silk," is taken from the cocoon in one continuous thread which may be several hundred yards long. In manufacturing reeled silk, many defective cocoons are found in which the fibers are not perfect or are broken. The silk from these cocoons may be treated like a short fiber and spun into threads varying in strength according to the length of the fibers. This so-called "spun" silk has not the high luster nor strength of "reeled" silk, but is often used as warp with reeled silk filling, or in imitation pongee, and back of satins, velvets, and in many other ways.*

Fig. 60

Fig. 60. - Silk fiber, showing the two minute filaments from the spinnerets of the silk worm and the gum which at first holds these two filaments together.

In the raw state, silk is sold by the pound. Three thousand silkworms are required to spin one pound of silk, and one to two pounds are required for a dress. When these figures are considered, it will be seen why good silk must necessarily be expensive. There is, however, a demand for a product at a moderate price, and in order to satisfy it, the manufacturer resorts to methods of adulteration.