The element of a right balance between the back and face has to be considered, and if care be not taken in the proper adjustment of the stock the result may be that one side of the goods will assert control over the other in such a manner as to prevent it lying flat and even. When such a web is cut it will curl up so as to be almost uncontrollable. Such a condition may arise from a variety of causes. If the weaves of the face and back cloths are identical then it will be necessary to have the face and back warps of the same size yarn or its equivalent. For instance, should the face be a four-thread plain and 40/2 is used, and the back only two threads, then the yarn used for the back warp must be 20/2 so as to equal the four threads of 40/2 in the face. Should, however, the face be a more open weave than the back, then an equal weight of yarn in both cloths will not be right, and it will be necessary to use yarn of a heavier weight for the face to compensate for the freedom of the more open weave and effect a proper balance with the more tightly woven back. There can be no fixed rule to apply to this, and only experience will indicate the proper relationship between the two. In Figs. 6 and 6A are shown the simplest form of double cloth, known as a plain web. By carefully following the weave it will be seen that while the face weaves 3 up and 1 down, and the back 1 up and 3 down, the filling will appear both on the face and back of the goods as 1 up and 1 down. If the binder was not there it would be a tubular web, having the same appearance all around. The binder, however, intersects the upper and lower cloths at each pick and binds the two together in one complete whole, while the rubber lies between the two, each strand being separated by the interlocking binder threads. It becomes necessary in order properly to connect the upper and lower cloths at their extreme edges to use a selvage warp, which as will be seen in Fig. 6A is drawn in on all four face and back harnesses, and the threads of which are arranged so as to complete the weave all around. To do this it will be seen that there is an odd thread at one side, otherwise the weave at this point would show two threads operating together next to each other, and would break up the continuity of the weave. [Illustration: Fig. 7.—Method of Banking a Set of Warps for Double Cloth Webs] The selvage plays an important part in the structure and weaving of the web. It forms the pocket for covering in which lies the outside rubber threads, and it must be so arranged that these threads can function properly so as to make a piece of goods that will lie flat. In the first place the yarn must be of such a size that with the proper number of threads employed the selvage will contract uniformly with the body of the goods, so that the web will not “frill” on account of a too heavy selvage, or “belly” because it is too light. CARE FOR SELVAGE