17. Rounding
As soon as the glue has stiffened but before it is hard the book is rounded. This must be done by experts and is a process which must be seen to be understood. The book is placed on the table with the fore edge toward the workman who then hammers the part of the back lying uppermost in such a way as to force the upper part of the book toward the workman. The book is then turned over and the process repeated. After a few operations like this the back of the book becomes rounded and the fore edge concave.
18. Backing
The book is then placed in a backing press allowing about an eighth of an inch to project, and screwed very tight. With a backing hammer the rounding process is continued and the sides of the book forced down over the edge of the press to form a projection against which the edge of the board for the side rests, forming the joint. In hammering, the workman begins at the proper distance from the center of the back so that he can force the backs of the other signatures over on each side toward the edge. (Fig. 9.)
Figure 9.—A book rounded and backed.
This process is the most important one in forwarding, calling for skilled labor. If the hammer is not used in exactly the right way the backs of the signatures may be crushed in, the stitches broken, or the paper or bands cut. In any case the book is materially weakened. A good workman will make a sharp joint and round the book perfectly without injuring its strength in any way.
19. Back Lining
All books have a lining of one kind or another on the back. Machine-bound books are generally lined with a coarse "super," as it is called in this country, or "mull" as it is called in England. Some library binders use a thin muslin, but the best material is canton flannel cut in strips wide enough to cover the back of the book and also to project about one inch on each side. The back of the book is glued, while the nap or fuzzy side of the canton flannel is pasted and then put on the back and well rubbed down. It is very important that both the glue and the paste be used. Experience has proved that when only one is used the canton flannel will come off, but when both are used, it becomes an integral part of the book.
The flannel which projects on the sides must be pasted to the end papers. When the paste and the glue have dried, the canton flannel shrinks tight to the back and adds materially to the strength of the book. After drying the flannel is trimmed at the head and tail close to the back.