A Plan for Studying Your Materials. - It is a good plan for three or four girls to put their samples together and work with each other while they are studying about materials. Is it not easy for you to see that all of these samples are not made of the same fiber? Sort your samples into piles of cotton, wool, silk and linen and while you are studying the following pages examine them to see if you have put them into their proper places.
How to Know Cotton. - Let us first study the samples you have that you think are made of cotton. If some one should ask you how you tell that these samples are made of cotton you might reply as follows:
1. Cotton has certain characteristics. It is generally described as being soft in feeling and dull in appearance. Examine your sample and try to think of other words to describe the feel and appearance of cotton. Examine the cotton fiber in a cotton boll and you will understand why cotton cloth has a soft feeling and dull appearance. Although the cotton fiber in its natural state is dull in appearance it is sometimes treated with a finishing process, called merceriza-tion, which gives the cotton a sheen somewhat like silk. Some shiny fabrics, therefore, may be cotton. You will learn more about this when you study finishing processes. Notice that these cotton fibers are like little hairs growing out from the seeds.
2. Another way to distinguish cotton is to unravel a piece of yarn from some cloth. Then untwist the yarn until the fibers are separated. The cotton fiber has a wavy appearance and varies in length from about ½ inch to 2 ½ inches. The length of the cotton fiber helps greatly to affect the appearance and texture of cotton cloth. The short fibers make a tiny fuzz on the surface of the material and a longer fiber makes a smoother finish. Can you see this tiny fuzz on any of your samples of underwear or dress materials?
3. Amore definite way of recognizing the cotton fiber is to look at it under the microscope. It looks like a twisted ribbon as shown in Fig. 79. It is because of this twist that it is easy to spin cotton into yarn. As you examine a piece of cotton material does it not seem marvelous that it is made of these tiny, twisted fibers? If you do not have any microscope in your classroom perhaps your science teacher will show you the cotton fiber under the microscope in the science laboratory.
How to Know Wool. - Examine all the samples which you think are wool. Try to find out what are the special characteristics of the wool fiber before you read the following paragraphs.
1. Select a cotton and a wool sample from your collection and lay them on the table in front of you. Shut your eyes and pick up the samples. Feel of them and see if you can always tell which is the wool by the springy, wiry feeling. Give other words which describe the appearance and feel of a woolen material.
2. Untwist a wool yarn just as you did the cotton yarn and compare a wool fiber with a cotton fiber. The wool fiber is like a crinkly, little hair. It may vary in length from one inch to fifteen inches. How does this compare with the cotton fiber? The length of the average wool fiber is about four inches. About how long is the fiber which you untwisted? The length of the wool fiber affects the smoothness of the wool cloth. The longer the fiber, the smoother and more lustrous the surface of the cloth will be. The shorter fibers leave fuzzy ends raised from the surface of the cloth.
3. Under the microscope you can see that the wool fiber is covered with tiny little scales that overlap as the scales of a fish do. See Fig. 80. These scales catch into each other and make it easy to spin the wool fibers into yarn. It is because of these scales on the wool fiber that it requires special care in laundering woolen materials. Changing from hot to cold water and rubbing the material while washing causes the scales to interlock with each other more firmly and to shrink. If you wash a pair of wool stockings in very hot water, rinse them in cold water, and wring them out hard, they may become very much shrunken, harsh and matted because of the action of the scales on the wool fiber. Have you any pieces in your collection of woolen samples that have been shrunk by improper washing?
How to Know Silk. - It is easy to select the samples that are made of silk and it is easy to think of words that describe its appearance and feel. Can you suggest the words that describe silk?
1. Untwist a silk thread and examine the fibers. Silk fibers are straight and smooth. It is astonishing to learn that the silk fiber is many hundred yards long. This means that the average silk fiber is longer than the silk thread that is wound on a spool of sewing silk. These spools generally contain 50 or 100 yards.
It is interesting to know how the silk fiber is made. The silkworm spins a cocoon just as a caterpillar does. However, the silkworm spins his cocoon out of a substance which we call silk. The first picture in Fig. 81 shows a silkworm feeding on a mulberry leaf, the second picture shows a finished cocoon and the third picture shows two cocoons, one with a hole where the moth escaped. This means that the silk fibers have been broken. Instead of being one continuous thread there will be many short ones. These short fibers are called waste silk and must be spun together just as the cotton fibers are spun. From the other cocoon come the very long fibers mentioned before. The moth was not allowed to escape from this cocoon but was killed by putting the cocoon in steam or boiling water. The long, unbroken fibers make a cloth with a more beautiful texture because there are no fiber ends sticking up from the surface of the material. If you find that little ends of fiber show on the surface of any of your samples you will know that they are probably made from waste silk.