As early as the fifteenth century, in the case of printed books on paper, this fault of the back falling in led some few binders to neutralise it by giving the back of the book a rounded form by means of hammering, and this quite prevented the falling in of the back. The exact extent of the rounding can easily be seen by looking at the front edge of a book, because the curves of the back and front correspond. The boards, however, remained in their first position, flat on the outer sheets.
Fig. 42.—Book with rounded back.
But another trouble was apparent in both these cases, namely, that when such books were opened, the joint between the boards and the back showed a tendency to pull up the few pages next adjacent. In time these pages became torn and injured, and constructively there was something wrong with the principle of attachment.
Paper is soft, and when a “rounded” book was fitted with hard boards and strongly pressed there would be a certain tendency for the boards to sink into the mass of the paper and to throw up a small ridge along the edge of the back. Such a small accidental ridge is often found on old paper books.
Fig. 43.—Book with back rounded and backed.
Fig. 44.—Book rounded and backed, before the boards are put on.
But there is no doubt that the actual process of making an intentional groove for the boards to fit in was practised by a few fifteenth century binders in England. This groove is made by an extension of the process of rounding the back, and it is produced by hammering the back over two hard boards carefully placed in the proper position. The shape of a back thus treated is theoretically as shown in Fig. 44, and it will be seen that the actual joint now falls away from the body of the book and is removed to the artificial line along the outer edge of the groove, and from this line the projecting bands are drawn in to the boards. If this operation of “backing” is properly done it is almost impossible for the back of a book to fall in. It will always open easily and return to its original form, and if the bands are properly attached to the boards, the latter will never fall off.