In fabrics that have been fulled, raised, and cropped, as buckskin, flannel, etc., the direction of the nap will indicate the direction of the warp, since the nap runs in this direction.
In the case of fabrics with doubled and single threads, the doubled threads are always found in the warp.
In fabrics composed of cotton and woolen threads running in different directions, the cotton yarn usually forms the warp and the woolen yarn the filling. Then again the warp threads of all fabrics are more tightly twisted than the filling threads, and are separated at more regular intervals.
Sometimes in stiffened or starched goods threads running in only one direction can be seen. In this case they are the warp threads.
If one set of threads appears stiffer and straighter than the other, the former may be regarded as warp, while the rough and crooked threads are the filling. The yarn also gives one a hint, since the better, longer, and higher number material constitutes the warp, while the thicker yarn the filling.
The direction of the twist of the thread is conclusive; if one set has a strong right twist and the other a left twist the first is the warp.
After determining the direction of the warp and filling, the next point is to determine the interlacing of the warp and filling threads—the weave. This may be done by inspection or by means of a pick-glass and needle. The weave may be plotted on design paper (plotting paper), the projecting warp threads being indicated by filling up the corresponding square, and leaving those referring to the filling threads blank. In this way the weaving pattern of the sample is obtained, and serves as a guide to the weaver in making the fabric, as well as for the preparation of the pattern cards for the Jacquard loom.
Testing the Strength and Elasticity of a Fabric. The old-fashioned plan of testing cloth by tearing it by the hand is unreliable, because tearing frequently requires only a certain skilled knack whereby the best material can be pulled in two. In this way an experienced man may tell good from bad cloth, but he cannot determine slight differences in quality, because he has exerted his strength so often that his capacity to distinguish the actual force has disappeared.
The best means of determining the strength of a fabric is by means of a mechanical dynamometer,[19] which expresses the tensile strength of the fabric in terms of weight. The machine is very useful to the manufacturer because it enables him to compare accurately his various products with those of his competitors. The value of these tests is sufficiently proved by the fact that all army clothing departments, etc., require their supplies of cloth, etc., to pass a definite test for strength.
Breaking tests also afford the most certain proof to bleachers of cotton and linen goods as to whether the bleaching has burned or weakened the goods. The same test will quickly determine whether a fabric has been improperly treated in the laundry.